| Message ID | 20170326161101.3542-1-michael@niedermayer.cc |
|---|---|
| State | New |
| Headers | show |
On Sun, 26 Mar 2017 18:11:01 +0200 Michael Niedermayer <michael@niedermayer.cc> wrote: > Fixes: 943/clusterfuzz-testcase-5114865297391616 > > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> > --- > libavcodec/mjpegdec.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c > index f26e8a3f9a..e08b045fe7 100644 > --- a/libavcodec/mjpegdec.c > +++ b/libavcodec/mjpegdec.c > @@ -757,7 +757,8 @@ static int decode_block_progressive(MJpegDecodeContext *s, int16_t *block, > uint16_t *quant_matrix, > int ss, int se, int Al, int *EOBRUN) > { > - int code, i, j, level, val, run; > + int code, i, j, val, run; > + SUINT level; > > if (*EOBRUN) { > (*EOBRUN)--; Please make the type either signed or unsigned. Making it both (depending on the debug level) just to make the fuzzer happy (or something more complicated than that?) isn't a good idea. You probably want to make it always unsigned?
On Sun, Mar 26, 2017 at 06:51:11PM +0200, wm4 wrote: > On Sun, 26 Mar 2017 18:11:01 +0200 > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > Fixes: 943/clusterfuzz-testcase-5114865297391616 > > > > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg > > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> > > --- > > libavcodec/mjpegdec.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c > > index f26e8a3f9a..e08b045fe7 100644 > > --- a/libavcodec/mjpegdec.c > > +++ b/libavcodec/mjpegdec.c > > @@ -757,7 +757,8 @@ static int decode_block_progressive(MJpegDecodeContext *s, int16_t *block, > > uint16_t *quant_matrix, > > int ss, int se, int Al, int *EOBRUN) > > { > > - int code, i, j, level, val, run; > > + int code, i, j, val, run; > > + SUINT level; > > > > if (*EOBRUN) { > > (*EOBRUN)--; > > Please make the type either signed or unsigned. Making it both > (depending on the debug level) just to make the fuzzer happy (or > something more complicated than that?) isn't a good idea. You probably > want to make it always unsigned? No, i want to make it SUINT If it is always unsigned then its not possible to detect overflows without explicitly checking for overflows. If it is SUINT then ubsan can be used to detect overflows, this is usefull to test files showing artifacts but no decode errors. [...]
On Sun, 26 Mar 2017 19:16:26 +0200 Michael Niedermayer <michael@niedermayer.cc> wrote: > On Sun, Mar 26, 2017 at 06:51:11PM +0200, wm4 wrote: > > On Sun, 26 Mar 2017 18:11:01 +0200 > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > Fixes: 943/clusterfuzz-testcase-5114865297391616 > > > > > > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg > > > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> > > > --- > > > libavcodec/mjpegdec.c | 3 ++- > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c > > > index f26e8a3f9a..e08b045fe7 100644 > > > --- a/libavcodec/mjpegdec.c > > > +++ b/libavcodec/mjpegdec.c > > > @@ -757,7 +757,8 @@ static int decode_block_progressive(MJpegDecodeContext *s, int16_t *block, > > > uint16_t *quant_matrix, > > > int ss, int se, int Al, int *EOBRUN) > > > { > > > - int code, i, j, level, val, run; > > > + int code, i, j, val, run; > > > + SUINT level; > > > > > > if (*EOBRUN) { > > > (*EOBRUN)--; > > > > Please make the type either signed or unsigned. Making it both > > (depending on the debug level) just to make the fuzzer happy (or > > something more complicated than that?) isn't a good idea. You probably > > want to make it always unsigned? > > No, i want to make it SUINT > > If it is always unsigned then its not possible to detect overflows > without explicitly checking for overflows. > If it is SUINT then ubsan can be used to detect overflows, this is > usefull to test files showing artifacts but no decode errors. > The point of these tools (static analyzers, sanitizers, fuzzers) is to improve the correctness of the code. SUINT is still defined to "int" if CHECKED is not defined (which in turn is only defined if DEBUG is defined, or if it was specified in CFLAGS, apparently). So this doesn't fix/improve the code. It only makes the analyzer happy. There is no point in this. Either the "normal" code is still buggy, then it should be fixed, or it's not - then the code doesn't need to be changed. Having subtly different correctness between code compiled in debug and release mode works against what you want to achieve with these tools. The only purpose of these changes seems to be to make the tools happy, while actually running different code for normal builds, which might lead to errors in that code being hidden.
On Sun, Mar 26, 2017 at 07:41:58PM +0200, wm4 wrote: > On Sun, 26 Mar 2017 19:16:26 +0200 > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > On Sun, Mar 26, 2017 at 06:51:11PM +0200, wm4 wrote: > > > On Sun, 26 Mar 2017 18:11:01 +0200 > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > Fixes: 943/clusterfuzz-testcase-5114865297391616 > > > > > > > > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg > > > > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> > > > > --- > > > > libavcodec/mjpegdec.c | 3 ++- > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c > > > > index f26e8a3f9a..e08b045fe7 100644 > > > > --- a/libavcodec/mjpegdec.c > > > > +++ b/libavcodec/mjpegdec.c > > > > @@ -757,7 +757,8 @@ static int decode_block_progressive(MJpegDecodeContext *s, int16_t *block, > > > > uint16_t *quant_matrix, > > > > int ss, int se, int Al, int *EOBRUN) > > > > { > > > > - int code, i, j, level, val, run; > > > > + int code, i, j, val, run; > > > > + SUINT level; > > > > > > > > if (*EOBRUN) { > > > > (*EOBRUN)--; > > > > > > Please make the type either signed or unsigned. Making it both > > > (depending on the debug level) just to make the fuzzer happy (or > > > something more complicated than that?) isn't a good idea. You probably > > > want to make it always unsigned? > > > > No, i want to make it SUINT > > > > If it is always unsigned then its not possible to detect overflows > > without explicitly checking for overflows. > > If it is SUINT then ubsan can be used to detect overflows, this is > > usefull to test files showing artifacts but no decode errors. > > > > The point of these tools (static analyzers, sanitizers, fuzzers) is to > improve the correctness of the code. > SUINT is still defined to "int" if > CHECKED is not defined no internal.h: #ifdef CHECKED #define SUINT int #define SUINT32 int32_t #else #define SUINT unsigned #define SUINT32 uint32_t #endif I belive the rest of your mail assumes this condition is backward to how it is SUINT is not there to make any tools happy its there to allow finding overflows in debug more while having valid c code in normal builds [...]
Hi, On Sun, Mar 26, 2017 at 3:31 PM, Michael Niedermayer <michael@niedermayer.cc > wrote: > On Sun, Mar 26, 2017 at 07:41:58PM +0200, wm4 wrote: > > On Sun, 26 Mar 2017 19:16:26 +0200 > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > On Sun, Mar 26, 2017 at 06:51:11PM +0200, wm4 wrote: > > > > On Sun, 26 Mar 2017 18:11:01 +0200 > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > Fixes: 943/clusterfuzz-testcase-5114865297391616 > > > > > > > > > > Found-by: continuous fuzzing process > https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg > > > > > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> > > > > > --- > > > > > libavcodec/mjpegdec.c | 3 ++- > > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c > > > > > index f26e8a3f9a..e08b045fe7 100644 > > > > > --- a/libavcodec/mjpegdec.c > > > > > +++ b/libavcodec/mjpegdec.c > > > > > @@ -757,7 +757,8 @@ static int decode_block_progressive(MJpegDecodeContext > *s, int16_t *block, > > > > > uint16_t *quant_matrix, > > > > > int ss, int se, int Al, int > *EOBRUN) > > > > > { > > > > > - int code, i, j, level, val, run; > > > > > + int code, i, j, val, run; > > > > > + SUINT level; > > > > > > > > > > if (*EOBRUN) { > > > > > (*EOBRUN)--; > > > > > > > > Please make the type either signed or unsigned. Making it both > > > > (depending on the debug level) just to make the fuzzer happy (or > > > > something more complicated than that?) isn't a good idea. You > probably > > > > want to make it always unsigned? > > > > > > No, i want to make it SUINT > > > > > > If it is always unsigned then its not possible to detect overflows > > > without explicitly checking for overflows. > > > If it is SUINT then ubsan can be used to detect overflows, this is > > > usefull to test files showing artifacts but no decode errors. > > > > > > > The point of these tools (static analyzers, sanitizers, fuzzers) is to > > improve the correctness of the code. > > > SUINT is still defined to "int" if > > CHECKED is not defined > > no > > internal.h: > #ifdef CHECKED > #define SUINT int > #define SUINT32 int32_t > #else > #define SUINT unsigned > #define SUINT32 uint32_t > #endif > > I belive the rest of your mail assumes this condition is backward to > how it is > > SUINT is not there to make any tools happy its there to allow finding > overflows in debug more while having valid c code in normal builds Why don't we want to detect overflows in debug mode? I somewhat agree with wm4's concern about SUINT. The answer is probably "we don't want to clip coefficients read from bitstreams" (e.g. for performance reasons, or because the bitstream provides no limits for such values, especially not pre-dequant), which means fuzzed files can have any value coefficient and signed arithmetic can thus cause undefined behaviour. If that is true, then both of the following are true: - (in release builds) signed arithmetic overflows and the resulting undefined behaviour for artifically crafted input are not a security concern. - (in debug builds) signed arithmetic overflows and the resulting undefined behaviour for artificially crafted input are a significant security concern, so much that we have added specific code to deal with them. However, these two are in direct violation with each other. As such, if one is true, the other one is by definition false. Which one is right? Ronald
On Sun, Mar 26, 2017 at 05:30:05PM -0400, Ronald S. Bultje wrote: > Hi, > > On Sun, Mar 26, 2017 at 3:31 PM, Michael Niedermayer <michael@niedermayer.cc > > wrote: > > > On Sun, Mar 26, 2017 at 07:41:58PM +0200, wm4 wrote: > > > On Sun, 26 Mar 2017 19:16:26 +0200 > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > On Sun, Mar 26, 2017 at 06:51:11PM +0200, wm4 wrote: > > > > > On Sun, 26 Mar 2017 18:11:01 +0200 > > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > > > Fixes: 943/clusterfuzz-testcase-5114865297391616 > > > > > > > > > > > > Found-by: continuous fuzzing process > > https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg > > > > > > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> > > > > > > --- > > > > > > libavcodec/mjpegdec.c | 3 ++- > > > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > > > > > diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c > > > > > > index f26e8a3f9a..e08b045fe7 100644 > > > > > > --- a/libavcodec/mjpegdec.c > > > > > > +++ b/libavcodec/mjpegdec.c > > > > > > @@ -757,7 +757,8 @@ static int decode_block_progressive(MJpegDecodeContext > > *s, int16_t *block, > > > > > > uint16_t *quant_matrix, > > > > > > int ss, int se, int Al, int > > *EOBRUN) > > > > > > { > > > > > > - int code, i, j, level, val, run; > > > > > > + int code, i, j, val, run; > > > > > > + SUINT level; > > > > > > > > > > > > if (*EOBRUN) { > > > > > > (*EOBRUN)--; > > > > > > > > > > Please make the type either signed or unsigned. Making it both > > > > > (depending on the debug level) just to make the fuzzer happy (or > > > > > something more complicated than that?) isn't a good idea. You > > probably > > > > > want to make it always unsigned? > > > > > > > > No, i want to make it SUINT > > > > > > > > If it is always unsigned then its not possible to detect overflows > > > > without explicitly checking for overflows. > > > > If it is SUINT then ubsan can be used to detect overflows, this is > > > > usefull to test files showing artifacts but no decode errors. > > > > > > > > > > The point of these tools (static analyzers, sanitizers, fuzzers) is to > > > improve the correctness of the code. > > > > > SUINT is still defined to "int" if > > > CHECKED is not defined > > > > no > > > > internal.h: > > #ifdef CHECKED > > #define SUINT int > > #define SUINT32 int32_t > > #else > > #define SUINT unsigned > > #define SUINT32 uint32_t > > #endif > > > > I belive the rest of your mail assumes this condition is backward to > > how it is > > > > SUINT is not there to make any tools happy its there to allow finding > > overflows in debug more while having valid c code in normal builds > > > Why don't we want to detect overflows in debug mode? like wm4 you read "#if A" as "#if not A", all your mail and questions seem based on reading the condition for SUINT flipped around in DEBUG mode CHECKED is enabled, SUINT is int and overflows are undefined behaviour which can be detected easily with ubsan. This allows us to debug samples producing artifacts but no decode errors due to overflows. in normal mode CHECKED is disabled, SUINT is unsigned and overflows are defined behavior. There must be no undefined behavior in releases maybe you belive everyone is using debug mode and the fuzzers run in debug mode. Maybe this is why everyone belives the condition is backward I might be wrong but unless you manually pass -DDEBUG you dont use debug mode, adding -DDEBUG is how our debug mode fate client tests that mode [...]
Hi, On Sun, Mar 26, 2017 at 6:41 PM, Michael Niedermayer <michael@niedermayer.cc > wrote: > On Sun, Mar 26, 2017 at 05:30:05PM -0400, Ronald S. Bultje wrote: > > Hi, > > > > On Sun, Mar 26, 2017 at 3:31 PM, Michael Niedermayer > <michael@niedermayer.cc > > > wrote: > > > > > On Sun, Mar 26, 2017 at 07:41:58PM +0200, wm4 wrote: > > > > On Sun, 26 Mar 2017 19:16:26 +0200 > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > On Sun, Mar 26, 2017 at 06:51:11PM +0200, wm4 wrote: > > > > > > On Sun, 26 Mar 2017 18:11:01 +0200 > > > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > > > > > Fixes: 943/clusterfuzz-testcase-5114865297391616 > > > > > > > > > > > > > > Found-by: continuous fuzzing process > > > https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg > > > > > > > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> > > > > > > > --- > > > > > > > libavcodec/mjpegdec.c | 3 ++- > > > > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c > > > > > > > index f26e8a3f9a..e08b045fe7 100644 > > > > > > > --- a/libavcodec/mjpegdec.c > > > > > > > +++ b/libavcodec/mjpegdec.c > > > > > > > @@ -757,7 +757,8 @@ static int decode_block_progressive( > MJpegDecodeContext > > > *s, int16_t *block, > > > > > > > uint16_t *quant_matrix, > > > > > > > int ss, int se, int Al, > int > > > *EOBRUN) > > > > > > > { > > > > > > > - int code, i, j, level, val, run; > > > > > > > + int code, i, j, val, run; > > > > > > > + SUINT level; > > > > > > > > > > > > > > if (*EOBRUN) { > > > > > > > (*EOBRUN)--; > > > > > > > > > > > > Please make the type either signed or unsigned. Making it both > > > > > > (depending on the debug level) just to make the fuzzer happy (or > > > > > > something more complicated than that?) isn't a good idea. You > > > probably > > > > > > want to make it always unsigned? > > > > > > > > > > No, i want to make it SUINT > > > > > > > > > > If it is always unsigned then its not possible to detect overflows > > > > > without explicitly checking for overflows. > > > > > If it is SUINT then ubsan can be used to detect overflows, this is > > > > > usefull to test files showing artifacts but no decode errors. > > > > > > > > > > > > > The point of these tools (static analyzers, sanitizers, fuzzers) is > to > > > > improve the correctness of the code. > > > > > > > SUINT is still defined to "int" if > > > > CHECKED is not defined > > > > > > no > > > > > > internal.h: > > > #ifdef CHECKED > > > #define SUINT int > > > #define SUINT32 int32_t > > > #else > > > #define SUINT unsigned > > > #define SUINT32 uint32_t > > > #endif > > > > > > I belive the rest of your mail assumes this condition is backward to > > > how it is > > > > > > SUINT is not there to make any tools happy its there to allow finding > > > overflows in debug more while having valid c code in normal builds > > > > > > > Why don't we want to detect overflows in debug mode? > > like wm4 you read "#if A" as "#if not A", all your mail and questions > seem based on reading the condition for SUINT flipped around > > in DEBUG mode CHECKED is enabled, SUINT is int and overflows are > undefined behaviour which can be detected easily with ubsan. > > This allows us to debug samples producing artifacts but no decode > errors due to overflows. > > > in normal mode CHECKED is disabled, SUINT is unsigned and overflows > are defined behavior. There must be no undefined behavior in releases > > maybe you belive everyone is using debug mode and the fuzzers run in > debug mode. Maybe this is why everyone belives the condition is > backward > I might be wrong but unless you manually pass -DDEBUG you dont use > debug mode, adding -DDEBUG is how our debug mode fate client tests that > mode So apparently it's OK that my system is taken over by a carefully crafted sample posted on bugzilla? Ronald
2017-03-27 3:18 GMT+02:00 Ronald S. Bultje <rsbultje@gmail.com>: > So apparently it's OK that my system is taken over by a carefully > crafted sample posted on bugzilla? Please stop this! I don't know if and on what kind of mission you are (and it won't make a difference to me) but these kind of comments are simply not welcome. Carl Eugen
On Mon, 27 Mar 2017 00:41:05 +0200 Michael Niedermayer <michael@niedermayer.cc> wrote: > On Sun, Mar 26, 2017 at 05:30:05PM -0400, Ronald S. Bultje wrote: > > Hi, > > > > On Sun, Mar 26, 2017 at 3:31 PM, Michael Niedermayer <michael@niedermayer.cc > > > wrote: > > > > > On Sun, Mar 26, 2017 at 07:41:58PM +0200, wm4 wrote: > > > > On Sun, 26 Mar 2017 19:16:26 +0200 > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > On Sun, Mar 26, 2017 at 06:51:11PM +0200, wm4 wrote: > > > > > > On Sun, 26 Mar 2017 18:11:01 +0200 > > > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > > > > > Fixes: 943/clusterfuzz-testcase-5114865297391616 > > > > > > > > > > > > > > Found-by: continuous fuzzing process > > > https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg > > > > > > > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> > > > > > > > --- > > > > > > > libavcodec/mjpegdec.c | 3 ++- > > > > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c > > > > > > > index f26e8a3f9a..e08b045fe7 100644 > > > > > > > --- a/libavcodec/mjpegdec.c > > > > > > > +++ b/libavcodec/mjpegdec.c > > > > > > > @@ -757,7 +757,8 @@ static int decode_block_progressive(MJpegDecodeContext > > > *s, int16_t *block, > > > > > > > uint16_t *quant_matrix, > > > > > > > int ss, int se, int Al, int > > > *EOBRUN) > > > > > > > { > > > > > > > - int code, i, j, level, val, run; > > > > > > > + int code, i, j, val, run; > > > > > > > + SUINT level; > > > > > > > > > > > > > > if (*EOBRUN) { > > > > > > > (*EOBRUN)--; > > > > > > > > > > > > Please make the type either signed or unsigned. Making it both > > > > > > (depending on the debug level) just to make the fuzzer happy (or > > > > > > something more complicated than that?) isn't a good idea. You > > > probably > > > > > > want to make it always unsigned? > > > > > > > > > > No, i want to make it SUINT > > > > > > > > > > If it is always unsigned then its not possible to detect overflows > > > > > without explicitly checking for overflows. > > > > > If it is SUINT then ubsan can be used to detect overflows, this is > > > > > usefull to test files showing artifacts but no decode errors. > > > > > > > > > > > > > The point of these tools (static analyzers, sanitizers, fuzzers) is to > > > > improve the correctness of the code. > > > > > > > SUINT is still defined to "int" if > > > > CHECKED is not defined > > > > > > no > > > > > > internal.h: > > > #ifdef CHECKED > > > #define SUINT int > > > #define SUINT32 int32_t > > > #else > > > #define SUINT unsigned > > > #define SUINT32 uint32_t > > > #endif > > > > > > I belive the rest of your mail assumes this condition is backward to > > > how it is > > > > > > SUINT is not there to make any tools happy its there to allow finding > > > overflows in debug more while having valid c code in normal builds > > > > > > > Why don't we want to detect overflows in debug mode? > > like wm4 you read "#if A" as "#if not A", all your mail and questions > seem based on reading the condition for SUINT flipped around > > in DEBUG mode CHECKED is enabled, SUINT is int and overflows are > undefined behaviour which can be detected easily with ubsan. > > This allows us to debug samples producing artifacts but no decode > errors due to overflows. > > > in normal mode CHECKED is disabled, SUINT is unsigned and overflows > are defined behavior. There must be no undefined behavior in releases > > maybe you belive everyone is using debug mode and the fuzzers run in > debug mode. Maybe this is why everyone belives the condition is > backward How would we know this? Maybe I've been assuming too much in order to try to make sense out of it. > I might be wrong but unless you manually pass -DDEBUG you dont use > debug mode, adding -DDEBUG is how our debug mode fate client tests that > mode But why do you want to detect overflows in debug mode, if in release mode they're using unsigned arithmetic, which has defined overflows? Either the code is correct with unsigned - then it can use unsigned in both release and debug mode. Or it isn't - then there's another problem that is painted over (?) in release mode. Either way, it makes no sense to me.
On Wed, Mar 29, 2017 at 11:47:31AM +0200, wm4 wrote: > On Mon, 27 Mar 2017 00:41:05 +0200 > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > On Sun, Mar 26, 2017 at 05:30:05PM -0400, Ronald S. Bultje wrote: > > > Hi, > > > > > > On Sun, Mar 26, 2017 at 3:31 PM, Michael Niedermayer <michael@niedermayer.cc > > > > wrote: > > > > > > > On Sun, Mar 26, 2017 at 07:41:58PM +0200, wm4 wrote: > > > > > On Sun, 26 Mar 2017 19:16:26 +0200 > > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > > > On Sun, Mar 26, 2017 at 06:51:11PM +0200, wm4 wrote: > > > > > > > On Sun, 26 Mar 2017 18:11:01 +0200 > > > > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > > > > > > > Fixes: 943/clusterfuzz-testcase-5114865297391616 > > > > > > > > > > > > > > > > Found-by: continuous fuzzing process > > > > https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg > > > > > > > > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> > > > > > > > > --- > > > > > > > > libavcodec/mjpegdec.c | 3 ++- > > > > > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > > > diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c > > > > > > > > index f26e8a3f9a..e08b045fe7 100644 > > > > > > > > --- a/libavcodec/mjpegdec.c > > > > > > > > +++ b/libavcodec/mjpegdec.c > > > > > > > > @@ -757,7 +757,8 @@ static int decode_block_progressive(MJpegDecodeContext > > > > *s, int16_t *block, > > > > > > > > uint16_t *quant_matrix, > > > > > > > > int ss, int se, int Al, int > > > > *EOBRUN) > > > > > > > > { > > > > > > > > - int code, i, j, level, val, run; > > > > > > > > + int code, i, j, val, run; > > > > > > > > + SUINT level; > > > > > > > > > > > > > > > > if (*EOBRUN) { > > > > > > > > (*EOBRUN)--; > > > > > > > > > > > > > > Please make the type either signed or unsigned. Making it both > > > > > > > (depending on the debug level) just to make the fuzzer happy (or > > > > > > > something more complicated than that?) isn't a good idea. You > > > > probably > > > > > > > want to make it always unsigned? > > > > > > > > > > > > No, i want to make it SUINT > > > > > > > > > > > > If it is always unsigned then its not possible to detect overflows > > > > > > without explicitly checking for overflows. > > > > > > If it is SUINT then ubsan can be used to detect overflows, this is > > > > > > usefull to test files showing artifacts but no decode errors. > > > > > > > > > > > > > > > > The point of these tools (static analyzers, sanitizers, fuzzers) is to > > > > > improve the correctness of the code. > > > > > > > > > SUINT is still defined to "int" if > > > > > CHECKED is not defined > > > > > > > > no > > > > > > > > internal.h: > > > > #ifdef CHECKED > > > > #define SUINT int > > > > #define SUINT32 int32_t > > > > #else > > > > #define SUINT unsigned > > > > #define SUINT32 uint32_t > > > > #endif > > > > > > > > I belive the rest of your mail assumes this condition is backward to > > > > how it is > > > > > > > > SUINT is not there to make any tools happy its there to allow finding > > > > overflows in debug more while having valid c code in normal builds > > > > > > > > > > > Why don't we want to detect overflows in debug mode? > > > > like wm4 you read "#if A" as "#if not A", all your mail and questions > > seem based on reading the condition for SUINT flipped around > > > > in DEBUG mode CHECKED is enabled, SUINT is int and overflows are > > undefined behaviour which can be detected easily with ubsan. > > > > This allows us to debug samples producing artifacts but no decode > > errors due to overflows. > > > > > > in normal mode CHECKED is disabled, SUINT is unsigned and overflows > > are defined behavior. There must be no undefined behavior in releases > > > > maybe you belive everyone is using debug mode and the fuzzers run in > > debug mode. Maybe this is why everyone belives the condition is > > backward > > How would we know this? Maybe I've been assuming too much in order to > try to make sense out of it. > > > I might be wrong but unless you manually pass -DDEBUG you dont use > > debug mode, adding -DDEBUG is how our debug mode fate client tests that > > mode > > But why do you want to detect overflows in debug mode, if in release To debug. Like i want compiler warnings to "debug" or coverity warnings to find and correct bugs. == "debug" If a undamaged file triggers an overflow thats very likely a bug and a easy to fix one if one knows about the overflow. If one doesnt know of that overflow it can be very hard to find > mode they're using unsigned arithmetic, which has defined overflows? > > Either the code is correct with unsigned - then it can use unsigned in > both release and debug mode. Or it isn't - then there's another problem > that is painted over (?) in release mode. > > Either way, it makes no sense to me. > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
On Fri, 7 Apr 2017 02:17:37 +0200 Michael Niedermayer <michael@niedermayer.cc> wrote: > On Wed, Mar 29, 2017 at 11:47:31AM +0200, wm4 wrote: > > On Mon, 27 Mar 2017 00:41:05 +0200 > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > On Sun, Mar 26, 2017 at 05:30:05PM -0400, Ronald S. Bultje wrote: > > > > Hi, > > > > > > > > On Sun, Mar 26, 2017 at 3:31 PM, Michael Niedermayer <michael@niedermayer.cc > > > > > wrote: > > > > > > > > > On Sun, Mar 26, 2017 at 07:41:58PM +0200, wm4 wrote: > > > > > > On Sun, 26 Mar 2017 19:16:26 +0200 > > > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > > > > > On Sun, Mar 26, 2017 at 06:51:11PM +0200, wm4 wrote: > > > > > > > > On Sun, 26 Mar 2017 18:11:01 +0200 > > > > > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > > > > > > > > > Fixes: 943/clusterfuzz-testcase-5114865297391616 > > > > > > > > > > > > > > > > > > Found-by: continuous fuzzing process > > > > > https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg > > > > > > > > > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> > > > > > > > > > --- > > > > > > > > > libavcodec/mjpegdec.c | 3 ++- > > > > > > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > > > > > diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c > > > > > > > > > index f26e8a3f9a..e08b045fe7 100644 > > > > > > > > > --- a/libavcodec/mjpegdec.c > > > > > > > > > +++ b/libavcodec/mjpegdec.c > > > > > > > > > @@ -757,7 +757,8 @@ static int decode_block_progressive(MJpegDecodeContext > > > > > *s, int16_t *block, > > > > > > > > > uint16_t *quant_matrix, > > > > > > > > > int ss, int se, int Al, int > > > > > *EOBRUN) > > > > > > > > > { > > > > > > > > > - int code, i, j, level, val, run; > > > > > > > > > + int code, i, j, val, run; > > > > > > > > > + SUINT level; > > > > > > > > > > > > > > > > > > if (*EOBRUN) { > > > > > > > > > (*EOBRUN)--; > > > > > > > > > > > > > > > > Please make the type either signed or unsigned. Making it both > > > > > > > > (depending on the debug level) just to make the fuzzer happy (or > > > > > > > > something more complicated than that?) isn't a good idea. You > > > > > probably > > > > > > > > want to make it always unsigned? > > > > > > > > > > > > > > No, i want to make it SUINT > > > > > > > > > > > > > > If it is always unsigned then its not possible to detect overflows > > > > > > > without explicitly checking for overflows. > > > > > > > If it is SUINT then ubsan can be used to detect overflows, this is > > > > > > > usefull to test files showing artifacts but no decode errors. > > > > > > > > > > > > > > > > > > > The point of these tools (static analyzers, sanitizers, fuzzers) is to > > > > > > improve the correctness of the code. > > > > > > > > > > > SUINT is still defined to "int" if > > > > > > CHECKED is not defined > > > > > > > > > > no > > > > > > > > > > internal.h: > > > > > #ifdef CHECKED > > > > > #define SUINT int > > > > > #define SUINT32 int32_t > > > > > #else > > > > > #define SUINT unsigned > > > > > #define SUINT32 uint32_t > > > > > #endif > > > > > > > > > > I belive the rest of your mail assumes this condition is backward to > > > > > how it is > > > > > > > > > > SUINT is not there to make any tools happy its there to allow finding > > > > > overflows in debug more while having valid c code in normal builds > > > > > > > > > > > > > > > Why don't we want to detect overflows in debug mode? > > > > > > like wm4 you read "#if A" as "#if not A", all your mail and questions > > > seem based on reading the condition for SUINT flipped around > > > > > > in DEBUG mode CHECKED is enabled, SUINT is int and overflows are > > > undefined behaviour which can be detected easily with ubsan. > > > > > > This allows us to debug samples producing artifacts but no decode > > > errors due to overflows. > > > > > > > > > in normal mode CHECKED is disabled, SUINT is unsigned and overflows > > > are defined behavior. There must be no undefined behavior in releases > > > > > > maybe you belive everyone is using debug mode and the fuzzers run in > > > debug mode. Maybe this is why everyone belives the condition is > > > backward > > > > How would we know this? Maybe I've been assuming too much in order to > > try to make sense out of it. > > > > > I might be wrong but unless you manually pass -DDEBUG you dont use > > > debug mode, adding -DDEBUG is how our debug mode fate client tests that > > > mode > > > > > But why do you want to detect overflows in debug mode, if in release > > To debug. > Like i want compiler warnings to "debug" > or coverity warnings to find and correct bugs. == "debug" > > If a undamaged file triggers an overflow thats very likely a bug and > a easy to fix one if one knows about the overflow. > If one doesnt know of that overflow it can be very hard to find Then it's not a bug by definition, and you can ignore it.
On Fri, Apr 07, 2017 at 08:30:50AM +0200, wm4 wrote: > On Fri, 7 Apr 2017 02:17:37 +0200 > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > On Wed, Mar 29, 2017 at 11:47:31AM +0200, wm4 wrote: > > > On Mon, 27 Mar 2017 00:41:05 +0200 > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > On Sun, Mar 26, 2017 at 05:30:05PM -0400, Ronald S. Bultje wrote: > > > > > Hi, > > > > > > > > > > On Sun, Mar 26, 2017 at 3:31 PM, Michael Niedermayer <michael@niedermayer.cc > > > > > > wrote: > > > > > > > > > > > On Sun, Mar 26, 2017 at 07:41:58PM +0200, wm4 wrote: > > > > > > > On Sun, 26 Mar 2017 19:16:26 +0200 > > > > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > > > > > > > On Sun, Mar 26, 2017 at 06:51:11PM +0200, wm4 wrote: > > > > > > > > > On Sun, 26 Mar 2017 18:11:01 +0200 > > > > > > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > > > > > > > > > > > Fixes: 943/clusterfuzz-testcase-5114865297391616 > > > > > > > > > > > > > > > > > > > > Found-by: continuous fuzzing process > > > > > > https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg > > > > > > > > > > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> > > > > > > > > > > --- > > > > > > > > > > libavcodec/mjpegdec.c | 3 ++- > > > > > > > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > > > > > > > diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c > > > > > > > > > > index f26e8a3f9a..e08b045fe7 100644 > > > > > > > > > > --- a/libavcodec/mjpegdec.c > > > > > > > > > > +++ b/libavcodec/mjpegdec.c > > > > > > > > > > @@ -757,7 +757,8 @@ static int decode_block_progressive(MJpegDecodeContext > > > > > > *s, int16_t *block, > > > > > > > > > > uint16_t *quant_matrix, > > > > > > > > > > int ss, int se, int Al, int > > > > > > *EOBRUN) > > > > > > > > > > { > > > > > > > > > > - int code, i, j, level, val, run; > > > > > > > > > > + int code, i, j, val, run; > > > > > > > > > > + SUINT level; > > > > > > > > > > > > > > > > > > > > if (*EOBRUN) { > > > > > > > > > > (*EOBRUN)--; > > > > > > > > > > > > > > > > > > Please make the type either signed or unsigned. Making it both > > > > > > > > > (depending on the debug level) just to make the fuzzer happy (or > > > > > > > > > something more complicated than that?) isn't a good idea. You > > > > > > probably > > > > > > > > > want to make it always unsigned? > > > > > > > > > > > > > > > > No, i want to make it SUINT > > > > > > > > > > > > > > > > If it is always unsigned then its not possible to detect overflows > > > > > > > > without explicitly checking for overflows. > > > > > > > > If it is SUINT then ubsan can be used to detect overflows, this is > > > > > > > > usefull to test files showing artifacts but no decode errors. > > > > > > > > > > > > > > > > > > > > > > The point of these tools (static analyzers, sanitizers, fuzzers) is to > > > > > > > improve the correctness of the code. > > > > > > > > > > > > > SUINT is still defined to "int" if > > > > > > > CHECKED is not defined > > > > > > > > > > > > no > > > > > > > > > > > > internal.h: > > > > > > #ifdef CHECKED > > > > > > #define SUINT int > > > > > > #define SUINT32 int32_t > > > > > > #else > > > > > > #define SUINT unsigned > > > > > > #define SUINT32 uint32_t > > > > > > #endif > > > > > > > > > > > > I belive the rest of your mail assumes this condition is backward to > > > > > > how it is > > > > > > > > > > > > SUINT is not there to make any tools happy its there to allow finding > > > > > > overflows in debug more while having valid c code in normal builds > > > > > > > > > > > > > > > > > > > Why don't we want to detect overflows in debug mode? > > > > > > > > like wm4 you read "#if A" as "#if not A", all your mail and questions > > > > seem based on reading the condition for SUINT flipped around > > > > > > > > in DEBUG mode CHECKED is enabled, SUINT is int and overflows are > > > > undefined behaviour which can be detected easily with ubsan. > > > > > > > > This allows us to debug samples producing artifacts but no decode > > > > errors due to overflows. > > > > > > > > > > > > in normal mode CHECKED is disabled, SUINT is unsigned and overflows > > > > are defined behavior. There must be no undefined behavior in releases > > > > > > > > maybe you belive everyone is using debug mode and the fuzzers run in > > > > debug mode. Maybe this is why everyone belives the condition is > > > > backward > > > > > > How would we know this? Maybe I've been assuming too much in order to > > > try to make sense out of it. > > > > > > > I might be wrong but unless you manually pass -DDEBUG you dont use > > > > debug mode, adding -DDEBUG is how our debug mode fate client tests that > > > > mode > > > > > > > > But why do you want to detect overflows in debug mode, if in release > > > > To debug. > > Like i want compiler warnings to "debug" > > or coverity warnings to find and correct bugs. == "debug" > > > > If a undamaged file triggers an overflow thats very likely a bug and > > a easy to fix one if one knows about the overflow. > > If one doesnt know of that overflow it can be very hard to find > > Then it's not a bug by definition, and you can ignore it. overflows have been bugs in the past warnings have pointed to bugs in the past ubsan has pointed to bugs in the past The example is about a overflow bug causing wrong decoder output ubsan would find that is in the most generic sense, the example would fit any such bug and such bugs were found that way in the past. if you say these are not bugs by definition even though its quite obvious they are bugs then whatever you use as definition must be flawed. Or you misunderstood what i wrote. Again the key points are * ubsan does and did help finding bugs which otherwise are hard to find * using unsigned prevents ubsan from working * adding checks and warnings would slow the code down and become messy * using signed without checks is undefined behavior which is not ok for use of the code as its not valid C * using SUINT avoids the undefined behavior, avoids peppering the code with checks and warnings and still allows us to use ubsan to detect overflows when we need to Id like to apply the patch unless you or someone else objects. thanks [...]
Hi, On Fri, Apr 7, 2017 at 6:22 AM, Michael Niedermayer <michael@niedermayer.cc> wrote: > if you say these are not bugs by definition even though its > quite obvious they are bugs then whatever you use as definition must > be flawed. Or you misunderstood what i wrote. > That's hypocritical. Id like to apply the patch unless you or someone else objects. I really don't like this approach. I'd like you to try to find something more sensible that protects developer machines from bugs also. Ronald
On Fri, 7 Apr 2017 12:22:07 +0200 Michael Niedermayer <michael@niedermayer.cc> wrote: > On Fri, Apr 07, 2017 at 08:30:50AM +0200, wm4 wrote: > > On Fri, 7 Apr 2017 02:17:37 +0200 > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > On Wed, Mar 29, 2017 at 11:47:31AM +0200, wm4 wrote: > > > > On Mon, 27 Mar 2017 00:41:05 +0200 > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > On Sun, Mar 26, 2017 at 05:30:05PM -0400, Ronald S. Bultje wrote: > > > > > > Hi, > > > > > > > > > > > > On Sun, Mar 26, 2017 at 3:31 PM, Michael Niedermayer <michael@niedermayer.cc > > > > > > > wrote: > > > > > > > > > > > > > On Sun, Mar 26, 2017 at 07:41:58PM +0200, wm4 wrote: > > > > > > > > On Sun, 26 Mar 2017 19:16:26 +0200 > > > > > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > > > > > > > > > On Sun, Mar 26, 2017 at 06:51:11PM +0200, wm4 wrote: > > > > > > > > > > On Sun, 26 Mar 2017 18:11:01 +0200 > > > > > > > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > > > > > > > > > > > > > Fixes: 943/clusterfuzz-testcase-5114865297391616 > > > > > > > > > > > > > > > > > > > > > > Found-by: continuous fuzzing process > > > > > > > https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg > > > > > > > > > > > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> > > > > > > > > > > > --- > > > > > > > > > > > libavcodec/mjpegdec.c | 3 ++- > > > > > > > > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > > > > > > > > > diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c > > > > > > > > > > > index f26e8a3f9a..e08b045fe7 100644 > > > > > > > > > > > --- a/libavcodec/mjpegdec.c > > > > > > > > > > > +++ b/libavcodec/mjpegdec.c > > > > > > > > > > > @@ -757,7 +757,8 @@ static int decode_block_progressive(MJpegDecodeContext > > > > > > > *s, int16_t *block, > > > > > > > > > > > uint16_t *quant_matrix, > > > > > > > > > > > int ss, int se, int Al, int > > > > > > > *EOBRUN) > > > > > > > > > > > { > > > > > > > > > > > - int code, i, j, level, val, run; > > > > > > > > > > > + int code, i, j, val, run; > > > > > > > > > > > + SUINT level; > > > > > > > > > > > > > > > > > > > > > > if (*EOBRUN) { > > > > > > > > > > > (*EOBRUN)--; > > > > > > > > > > > > > > > > > > > > Please make the type either signed or unsigned. Making it both > > > > > > > > > > (depending on the debug level) just to make the fuzzer happy (or > > > > > > > > > > something more complicated than that?) isn't a good idea. You > > > > > > > probably > > > > > > > > > > want to make it always unsigned? > > > > > > > > > > > > > > > > > > No, i want to make it SUINT > > > > > > > > > > > > > > > > > > If it is always unsigned then its not possible to detect overflows > > > > > > > > > without explicitly checking for overflows. > > > > > > > > > If it is SUINT then ubsan can be used to detect overflows, this is > > > > > > > > > usefull to test files showing artifacts but no decode errors. > > > > > > > > > > > > > > > > > > > > > > > > > The point of these tools (static analyzers, sanitizers, fuzzers) is to > > > > > > > > improve the correctness of the code. > > > > > > > > > > > > > > > SUINT is still defined to "int" if > > > > > > > > CHECKED is not defined > > > > > > > > > > > > > > no > > > > > > > > > > > > > > internal.h: > > > > > > > #ifdef CHECKED > > > > > > > #define SUINT int > > > > > > > #define SUINT32 int32_t > > > > > > > #else > > > > > > > #define SUINT unsigned > > > > > > > #define SUINT32 uint32_t > > > > > > > #endif > > > > > > > > > > > > > > I belive the rest of your mail assumes this condition is backward to > > > > > > > how it is > > > > > > > > > > > > > > SUINT is not there to make any tools happy its there to allow finding > > > > > > > overflows in debug more while having valid c code in normal builds > > > > > > > > > > > > > > > > > > > > > > > Why don't we want to detect overflows in debug mode? > > > > > > > > > > like wm4 you read "#if A" as "#if not A", all your mail and questions > > > > > seem based on reading the condition for SUINT flipped around > > > > > > > > > > in DEBUG mode CHECKED is enabled, SUINT is int and overflows are > > > > > undefined behaviour which can be detected easily with ubsan. > > > > > > > > > > This allows us to debug samples producing artifacts but no decode > > > > > errors due to overflows. > > > > > > > > > > > > > > > in normal mode CHECKED is disabled, SUINT is unsigned and overflows > > > > > are defined behavior. There must be no undefined behavior in releases > > > > > > > > > > maybe you belive everyone is using debug mode and the fuzzers run in > > > > > debug mode. Maybe this is why everyone belives the condition is > > > > > backward > > > > > > > > How would we know this? Maybe I've been assuming too much in order to > > > > try to make sense out of it. > > > > > > > > > I might be wrong but unless you manually pass -DDEBUG you dont use > > > > > debug mode, adding -DDEBUG is how our debug mode fate client tests that > > > > > mode > > > > > > > > > > > But why do you want to detect overflows in debug mode, if in release > > > > > > To debug. > > > Like i want compiler warnings to "debug" > > > or coverity warnings to find and correct bugs. == "debug" > > > > > > If a undamaged file triggers an overflow thats very likely a bug and > > > a easy to fix one if one knows about the overflow. > > > If one doesnt know of that overflow it can be very hard to find > > > > > Then it's not a bug by definition, and you can ignore it. > > overflows have been bugs in the past > warnings have pointed to bugs in the past > ubsan has pointed to bugs in the past What I'm saying is: Either an overflow is a bug. Then you should not apply hacks like making all types unsigned just to hide these bugs not show up on sanitizers or static analyzers. And you shouldn't add another hack just to make them show up again in debug mode. You could argue that this is some kind of "hardening" technique (with the second hack still allowing debugging it), but how about let's not? Just fix overflows when you find them. Or the overflow is not a bug. Then the type should always be unsigned, because overflows would be relatively meaningless. Why make the source code harder to follow and add noise in debug mode just because of a vague idea that unknown overflows could occur and which could be bugs? If overflows are a problem, make the type always signed, and always fix overflows as you encounter them. As it looks like, SUINT only hides bugs, and serves the questionable idea that it's better to hide bugs for the sake of silencing undefined behavior. > > The example is about a overflow bug causing wrong decoder output > ubsan would find > that is in the most generic sense, the example would fit any such > bug and such bugs were found that way in the past. > > if you say these are not bugs by definition even though its > quite obvious they are bugs then whatever you use as definition must > be flawed. Or you misunderstood what i wrote. > > Again the key points are > * ubsan does and did help finding bugs which otherwise are hard to find > * using unsigned prevents ubsan from working > * adding checks and warnings would slow the code down and become messy > * using signed without checks is undefined behavior which is not ok for > use of the code as its not valid C > * using SUINT avoids the undefined behavior, avoids peppering the code > with checks and warnings and still allows us to use ubsan to detect > overflows when we need to > > Id like to apply the patch unless you or someone else objects. > > thanks > > [...]
On Fri, Apr 07, 2017 at 06:26:05AM -0400, Ronald S. Bultje wrote: > Hi, > > On Fri, Apr 7, 2017 at 6:22 AM, Michael Niedermayer <michael@niedermayer.cc> > wrote: > > > if you say these are not bugs by definition even though its > > quite obvious they are bugs then whatever you use as definition must > > be flawed. Or you misunderstood what i wrote. > > > > That's hypocritical. in what way ? > > Id like to apply the patch unless you or someone else objects. > > > I really don't like this approach. I'd like you to try to find something > more sensible that protects developer machines from bugs also. i suggested to decouple SUINT from the #ifdef DEBUG, which fixes exactly that possibility (and noone seemed to care) [...]
On Fri, Apr 07, 2017 at 12:35:37PM +0200, wm4 wrote: > On Fri, 7 Apr 2017 12:22:07 +0200 > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > On Fri, Apr 07, 2017 at 08:30:50AM +0200, wm4 wrote: > > > On Fri, 7 Apr 2017 02:17:37 +0200 > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > On Wed, Mar 29, 2017 at 11:47:31AM +0200, wm4 wrote: > > > > > On Mon, 27 Mar 2017 00:41:05 +0200 > > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > > > On Sun, Mar 26, 2017 at 05:30:05PM -0400, Ronald S. Bultje wrote: > > > > > > > Hi, > > > > > > > > > > > > > > On Sun, Mar 26, 2017 at 3:31 PM, Michael Niedermayer <michael@niedermayer.cc > > > > > > > > wrote: > > > > > > > > > > > > > > > On Sun, Mar 26, 2017 at 07:41:58PM +0200, wm4 wrote: > > > > > > > > > On Sun, 26 Mar 2017 19:16:26 +0200 > > > > > > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > > > > > > > > > > > On Sun, Mar 26, 2017 at 06:51:11PM +0200, wm4 wrote: > > > > > > > > > > > On Sun, 26 Mar 2017 18:11:01 +0200 > > > > > > > > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > > > > > > > > > > > > > > > Fixes: 943/clusterfuzz-testcase-5114865297391616 > > > > > > > > > > > > > > > > > > > > > > > > Found-by: continuous fuzzing process > > > > > > > > https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg > > > > > > > > > > > > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> > > > > > > > > > > > > --- > > > > > > > > > > > > libavcodec/mjpegdec.c | 3 ++- > > > > > > > > > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > > > > > > > > > > > diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c > > > > > > > > > > > > index f26e8a3f9a..e08b045fe7 100644 > > > > > > > > > > > > --- a/libavcodec/mjpegdec.c > > > > > > > > > > > > +++ b/libavcodec/mjpegdec.c > > > > > > > > > > > > @@ -757,7 +757,8 @@ static int decode_block_progressive(MJpegDecodeContext > > > > > > > > *s, int16_t *block, > > > > > > > > > > > > uint16_t *quant_matrix, > > > > > > > > > > > > int ss, int se, int Al, int > > > > > > > > *EOBRUN) > > > > > > > > > > > > { > > > > > > > > > > > > - int code, i, j, level, val, run; > > > > > > > > > > > > + int code, i, j, val, run; > > > > > > > > > > > > + SUINT level; > > > > > > > > > > > > > > > > > > > > > > > > if (*EOBRUN) { > > > > > > > > > > > > (*EOBRUN)--; > > > > > > > > > > > > > > > > > > > > > > Please make the type either signed or unsigned. Making it both > > > > > > > > > > > (depending on the debug level) just to make the fuzzer happy (or > > > > > > > > > > > something more complicated than that?) isn't a good idea. You > > > > > > > > probably > > > > > > > > > > > want to make it always unsigned? > > > > > > > > > > > > > > > > > > > > No, i want to make it SUINT > > > > > > > > > > > > > > > > > > > > If it is always unsigned then its not possible to detect overflows > > > > > > > > > > without explicitly checking for overflows. > > > > > > > > > > If it is SUINT then ubsan can be used to detect overflows, this is > > > > > > > > > > usefull to test files showing artifacts but no decode errors. > > > > > > > > > > > > > > > > > > > > > > > > > > > > The point of these tools (static analyzers, sanitizers, fuzzers) is to > > > > > > > > > improve the correctness of the code. > > > > > > > > > > > > > > > > > SUINT is still defined to "int" if > > > > > > > > > CHECKED is not defined > > > > > > > > > > > > > > > > no > > > > > > > > > > > > > > > > internal.h: > > > > > > > > #ifdef CHECKED > > > > > > > > #define SUINT int > > > > > > > > #define SUINT32 int32_t > > > > > > > > #else > > > > > > > > #define SUINT unsigned > > > > > > > > #define SUINT32 uint32_t > > > > > > > > #endif > > > > > > > > > > > > > > > > I belive the rest of your mail assumes this condition is backward to > > > > > > > > how it is > > > > > > > > > > > > > > > > SUINT is not there to make any tools happy its there to allow finding > > > > > > > > overflows in debug more while having valid c code in normal builds > > > > > > > > > > > > > > > > > > > > > > > > > > > Why don't we want to detect overflows in debug mode? > > > > > > > > > > > > like wm4 you read "#if A" as "#if not A", all your mail and questions > > > > > > seem based on reading the condition for SUINT flipped around > > > > > > > > > > > > in DEBUG mode CHECKED is enabled, SUINT is int and overflows are > > > > > > undefined behaviour which can be detected easily with ubsan. > > > > > > > > > > > > This allows us to debug samples producing artifacts but no decode > > > > > > errors due to overflows. > > > > > > > > > > > > > > > > > > in normal mode CHECKED is disabled, SUINT is unsigned and overflows > > > > > > are defined behavior. There must be no undefined behavior in releases > > > > > > > > > > > > maybe you belive everyone is using debug mode and the fuzzers run in > > > > > > debug mode. Maybe this is why everyone belives the condition is > > > > > > backward > > > > > > > > > > How would we know this? Maybe I've been assuming too much in order to > > > > > try to make sense out of it. > > > > > > > > > > > I might be wrong but unless you manually pass -DDEBUG you dont use > > > > > > debug mode, adding -DDEBUG is how our debug mode fate client tests that > > > > > > mode > > > > > > > > > > > > > > But why do you want to detect overflows in debug mode, if in release > > > > > > > > To debug. > > > > Like i want compiler warnings to "debug" > > > > or coverity warnings to find and correct bugs. == "debug" > > > > > > > > If a undamaged file triggers an overflow thats very likely a bug and > > > > a easy to fix one if one knows about the overflow. > > > > If one doesnt know of that overflow it can be very hard to find > > > > > > > > Then it's not a bug by definition, and you can ignore it. > > > > overflows have been bugs in the past > > warnings have pointed to bugs in the past > > ubsan has pointed to bugs in the past > > What I'm saying is: > > Either an overflow is a bug. Then you should not apply hacks like > making all types unsigned just to hide these bugs not show up on > sanitizers or static analyzers. And you shouldn't add another hack just > to make them show up again in debug mode. You could argue that this is > some kind of "hardening" technique (with the second hack still allowing > debugging it), but how about let's not? Just fix overflows when you > find them. > > Or the overflow is not a bug. Then the type should always be unsigned, > because overflows would be relatively meaningless. Why make the source > code harder to follow and add noise in debug mode just because of a > vague idea that unknown overflows could occur and which could be bugs? > If overflows are a problem, make the type always signed, and always fix > overflows as you encounter them. The problem is what we have is a useless fuzzed file triggering this the fuzzed file shows that the overflow can be triggered it tells us nothing about if its a real bug can it be triggered also by a file we want to support? if so its a real bug in some cases this can be awnsered by reading some specification still in reality what really matters if such files exist even if we have a spec and even if it does say what the range is. Some specs are non public, some lack detailed limits on intermediates of computations. We can spend a long time to determine if something is needed by a real file and thus a bug or not. This is what i generally do but often theres just no final clear yes or no. Theres a probably yes / probably no / maybe and for that SUINT comes in handy we fix the undefined behavior but if a user submits a file that doesnt decode correctly we can still flip a switch and use ubsan to see if it involves any overflows This is simply minimizing the time needed to debug such issues * spend more and more time to make really really sure nothing valid can trigger an overflow, no unexpected odd files exist, ... * vs just run files reported by users under ubsan You could also say iam trying to use our userbases time to help double check if what i think is likely not a bug really is not a bug [...]
On Fri, 7 Apr 2017 13:07:23 +0200 Michael Niedermayer <michael@niedermayer.cc> wrote: > On Fri, Apr 07, 2017 at 12:35:37PM +0200, wm4 wrote: > > On Fri, 7 Apr 2017 12:22:07 +0200 > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > On Fri, Apr 07, 2017 at 08:30:50AM +0200, wm4 wrote: > > > > On Fri, 7 Apr 2017 02:17:37 +0200 > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > On Wed, Mar 29, 2017 at 11:47:31AM +0200, wm4 wrote: > > > > > > On Mon, 27 Mar 2017 00:41:05 +0200 > > > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > > > > > On Sun, Mar 26, 2017 at 05:30:05PM -0400, Ronald S. Bultje wrote: > > > > > > > > Hi, > > > > > > > > > > > > > > > > On Sun, Mar 26, 2017 at 3:31 PM, Michael Niedermayer <michael@niedermayer.cc > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > On Sun, Mar 26, 2017 at 07:41:58PM +0200, wm4 wrote: > > > > > > > > > > On Sun, 26 Mar 2017 19:16:26 +0200 > > > > > > > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > > > > > > > > > > > > > On Sun, Mar 26, 2017 at 06:51:11PM +0200, wm4 wrote: > > > > > > > > > > > > On Sun, 26 Mar 2017 18:11:01 +0200 > > > > > > > > > > > > Michael Niedermayer <michael@niedermayer.cc> wrote: > > > > > > > > > > > > > > > > > > > > > > > > > Fixes: 943/clusterfuzz-testcase-5114865297391616 > > > > > > > > > > > > > > > > > > > > > > > > > > Found-by: continuous fuzzing process > > > > > > > > > https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg > > > > > > > > > > > > > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> > > > > > > > > > > > > > --- > > > > > > > > > > > > > libavcodec/mjpegdec.c | 3 ++- > > > > > > > > > > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > > > > > > > > > > > > > diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c > > > > > > > > > > > > > index f26e8a3f9a..e08b045fe7 100644 > > > > > > > > > > > > > --- a/libavcodec/mjpegdec.c > > > > > > > > > > > > > +++ b/libavcodec/mjpegdec.c > > > > > > > > > > > > > @@ -757,7 +757,8 @@ static int decode_block_progressive(MJpegDecodeContext > > > > > > > > > *s, int16_t *block, > > > > > > > > > > > > > uint16_t *quant_matrix, > > > > > > > > > > > > > int ss, int se, int Al, int > > > > > > > > > *EOBRUN) > > > > > > > > > > > > > { > > > > > > > > > > > > > - int code, i, j, level, val, run; > > > > > > > > > > > > > + int code, i, j, val, run; > > > > > > > > > > > > > + SUINT level; > > > > > > > > > > > > > > > > > > > > > > > > > > if (*EOBRUN) { > > > > > > > > > > > > > (*EOBRUN)--; > > > > > > > > > > > > > > > > > > > > > > > > Please make the type either signed or unsigned. Making it both > > > > > > > > > > > > (depending on the debug level) just to make the fuzzer happy (or > > > > > > > > > > > > something more complicated than that?) isn't a good idea. You > > > > > > > > > probably > > > > > > > > > > > > want to make it always unsigned? > > > > > > > > > > > > > > > > > > > > > > No, i want to make it SUINT > > > > > > > > > > > > > > > > > > > > > > If it is always unsigned then its not possible to detect overflows > > > > > > > > > > > without explicitly checking for overflows. > > > > > > > > > > > If it is SUINT then ubsan can be used to detect overflows, this is > > > > > > > > > > > usefull to test files showing artifacts but no decode errors. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > The point of these tools (static analyzers, sanitizers, fuzzers) is to > > > > > > > > > > improve the correctness of the code. > > > > > > > > > > > > > > > > > > > SUINT is still defined to "int" if > > > > > > > > > > CHECKED is not defined > > > > > > > > > > > > > > > > > > no > > > > > > > > > > > > > > > > > > internal.h: > > > > > > > > > #ifdef CHECKED > > > > > > > > > #define SUINT int > > > > > > > > > #define SUINT32 int32_t > > > > > > > > > #else > > > > > > > > > #define SUINT unsigned > > > > > > > > > #define SUINT32 uint32_t > > > > > > > > > #endif > > > > > > > > > > > > > > > > > > I belive the rest of your mail assumes this condition is backward to > > > > > > > > > how it is > > > > > > > > > > > > > > > > > > SUINT is not there to make any tools happy its there to allow finding > > > > > > > > > overflows in debug more while having valid c code in normal builds > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Why don't we want to detect overflows in debug mode? > > > > > > > > > > > > > > like wm4 you read "#if A" as "#if not A", all your mail and questions > > > > > > > seem based on reading the condition for SUINT flipped around > > > > > > > > > > > > > > in DEBUG mode CHECKED is enabled, SUINT is int and overflows are > > > > > > > undefined behaviour which can be detected easily with ubsan. > > > > > > > > > > > > > > This allows us to debug samples producing artifacts but no decode > > > > > > > errors due to overflows. > > > > > > > > > > > > > > > > > > > > > in normal mode CHECKED is disabled, SUINT is unsigned and overflows > > > > > > > are defined behavior. There must be no undefined behavior in releases > > > > > > > > > > > > > > maybe you belive everyone is using debug mode and the fuzzers run in > > > > > > > debug mode. Maybe this is why everyone belives the condition is > > > > > > > backward > > > > > > > > > > > > How would we know this? Maybe I've been assuming too much in order to > > > > > > try to make sense out of it. > > > > > > > > > > > > > I might be wrong but unless you manually pass -DDEBUG you dont use > > > > > > > debug mode, adding -DDEBUG is how our debug mode fate client tests that > > > > > > > mode > > > > > > > > > > > > > > > > > But why do you want to detect overflows in debug mode, if in release > > > > > > > > > > To debug. > > > > > Like i want compiler warnings to "debug" > > > > > or coverity warnings to find and correct bugs. == "debug" > > > > > > > > > > If a undamaged file triggers an overflow thats very likely a bug and > > > > > a easy to fix one if one knows about the overflow. > > > > > If one doesnt know of that overflow it can be very hard to find > > > > > > > > > > > Then it's not a bug by definition, and you can ignore it. > > > > > > overflows have been bugs in the past > > > warnings have pointed to bugs in the past > > > ubsan has pointed to bugs in the past > > > > What I'm saying is: > > > > Either an overflow is a bug. Then you should not apply hacks like > > making all types unsigned just to hide these bugs not show up on > > sanitizers or static analyzers. And you shouldn't add another hack just > > to make them show up again in debug mode. You could argue that this is > > some kind of "hardening" technique (with the second hack still allowing > > debugging it), but how about let's not? Just fix overflows when you > > find them. > > > > Or the overflow is not a bug. Then the type should always be unsigned, > > because overflows would be relatively meaningless. Why make the source > > code harder to follow and add noise in debug mode just because of a > > vague idea that unknown overflows could occur and which could be bugs? > > If overflows are a problem, make the type always signed, and always fix > > overflows as you encounter them. > > The problem is what we have is a useless fuzzed file triggering this > the fuzzed file shows that the overflow can be triggered it tells us > nothing about if its a real bug Look at the code and determine if it could be a bug or not? Changing a type to unsigned is a nice way to get rid of undefined behavior, but do it only if the result of an overflow does not matter. > can it be triggered also by a file we want to support? > if so its a real bug And how does SUINT help you make the decision? > in some cases this can be awnsered by reading some specification > still in reality what really matters if such files exist even if we > have a spec and even if it does say what the range is. > Some specs are non public, some lack detailed limits on intermediates > of computations. > > We can spend a long time to determine if something is needed by a > real file and thus a bug or not. > This is what i generally do but often theres just no final clear yes > or no. Theres a probably yes / probably no / maybe > and for that SUINT comes in handy > we fix the undefined behavior but if a user submits a file that doesnt > decode correctly we can still flip a switch and use ubsan to see if > it involves any overflows Well there are 3 reasons why you'd change signed to unsigned: 1. unsigned overflow actually gives the intended result 2. avoiding undefined behavior when the result does not matter 3. shutting up a fuzzer without fixing the actual issue None of these fix themselves when changing the type back to signed, except for operations which needed to be signed in the first place. I'm not sure how changing back to signed is supposed to help anyone with actual overflows, since these would have been buggy in the first place. Sure, it helps you better to spot a bug you could have spotted easier with the original code when all was still signed. But with 1. and 2. you'd have confidence in the change to unsigned. We don't add arbitrary ifdefs and typedefs to other code either, just because it'd help us to easily "revert" a change. And for 3. checking the overflow explicitly would have been better. So, you can fix the overflows by actually fixing the overflows, instead of switching the type to unsigned and hoping it doesn't break anything. And even if what you said about "flipping a switch" is true, you could just edit the source code at the questionable location, which in fact would be quicker than changing SUINT declared in a central location or rebuilding the entire FFmpeg to change the debug level. Maybe I'm indeed missing something here. > > This is simply minimizing the time needed to debug such issues > * spend more and more time to make really really sure nothing valid > can trigger an overflow, no unexpected odd files exist, ... > * vs just run files reported by users under ubsan > > You could also say iam trying to use our userbases time to help > double check if what i think is likely not a bug really is not a bug I don't see how any of this helps users. They don't run fuzzers or debug tools, and they are not going to try to change the definition of SUINT. If something is _really_ questionable we still could print an error message if a calculation overflows. That would _actually_ help finding the issue. (But please, let's not do this with every overflow check.)
Hi, On Fri, Apr 7, 2017 at 6:47 AM, Michael Niedermayer <michael@niedermayer.cc> wrote: > On Fri, Apr 07, 2017 at 06:26:05AM -0400, Ronald S. Bultje wrote: > > On Fri, Apr 7, 2017 at 6:22 AM, Michael Niedermayer > <michael@niedermayer.cc> > > > Id like to apply the patch unless you or someone else objects. > > > > I really don't like this approach. I'd like you to try to find something > > more sensible that protects developer machines from bugs also. > > i suggested to decouple SUINT from the #ifdef DEBUG, which fixes > exactly that possibility (and noone seemed to care) You asked - in this email - to apply this patch as-is. The patch does not decouple #ifdef DEBUG from SUINT. Now the question is whether SUINT has any raison d'etre in our main codebase. If it's under #if 0 or otherwise "dead code", any Diego'ification would immediately get rid of it. So answer me this question: if the code is under #if 0, why shouldn't it just exist locally on your hard disk only? (Yes, I have actual (old) debug branches for the vp9 decoder locally.) Ronald
On Fri, Apr 07, 2017 at 07:46:01AM -0400, Ronald S. Bultje wrote: > Hi, > > On Fri, Apr 7, 2017 at 6:47 AM, Michael Niedermayer <michael@niedermayer.cc> > wrote: > > > On Fri, Apr 07, 2017 at 06:26:05AM -0400, Ronald S. Bultje wrote: > > > On Fri, Apr 7, 2017 at 6:22 AM, Michael Niedermayer > > <michael@niedermayer.cc> > > > > Id like to apply the patch unless you or someone else objects. > > > > > > I really don't like this approach. I'd like you to try to find something > > > more sensible that protects developer machines from bugs also. > > > > i suggested to decouple SUINT from the #ifdef DEBUG, which fixes > > exactly that possibility (and noone seemed to care) > > > You asked - in this email - to apply this patch as-is. The patch does not > decouple #ifdef DEBUG from SUINT. I suggested it previously to decouple them. This patch is in no way related to the coupling, with or without the coupling the patch wouldnt change > > Now the question is whether SUINT has any raison d'etre in our main > codebase. If it's under #if 0 or otherwise "dead code", any Diego'ification > would immediately get rid of it. So answer me this question: if the code is > under #if 0, why shouldn't it just exist locally on your hard disk only? as has been said many times SUINT is essential to test for one class of bugs with ubsan. If its in a private branch, only i would test with it, only i would maintain it until i lost interrest and it bit rots, if that happens we lose the ability to test for this class of bugs do people want this ? > > (Yes, I have actual (old) debug branches for the vp9 decoder locally.) i have all kinds of branches too, but this isnt specific to a single codec or a single developer Do you maintain some branch that contains type changes accorss the codebase that you know you will need repeatly in the future ? [...]
diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c index f26e8a3f9a..e08b045fe7 100644 --- a/libavcodec/mjpegdec.c +++ b/libavcodec/mjpegdec.c @@ -757,7 +757,8 @@ static int decode_block_progressive(MJpegDecodeContext *s, int16_t *block, uint16_t *quant_matrix, int ss, int se, int Al, int *EOBRUN) { - int code, i, j, level, val, run; + int code, i, j, val, run; + SUINT level; if (*EOBRUN) { (*EOBRUN)--;
Fixes: 943/clusterfuzz-testcase-5114865297391616 Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> --- libavcodec/mjpegdec.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)