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[FFmpeg-devel,6/9] avformat/vividas: Check for zero v_size

Message ID 20201021223733.2563-6-michael@niedermayer.cc
State Accepted
Commit c7a5face77878ef0169a56a46d4320a41d52d3b5
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Series [FFmpeg-devel,1/9] avformat/segafilm: Check that there is a stream
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Commit Message

Michael Niedermayer Oct. 21, 2020, 10:37 p.m. UTC
Fixes: SEGV on unknown address 0x000000000000
Fixes: 26482/clusterfuzz-testcase-minimized-ffmpeg_dem_VIVIDAS_fuzzer-4905102324006912

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavformat/vividas.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Andreas Rheinhardt Oct. 22, 2020, 5:55 a.m. UTC | #1
Michael Niedermayer:
> Fixes: SEGV on unknown address 0x000000000000
> Fixes: 26482/clusterfuzz-testcase-minimized-ffmpeg_dem_VIVIDAS_fuzzer-4905102324006912
> 
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavformat/vividas.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/libavformat/vividas.c b/libavformat/vividas.c
> index 999c4a5d1c..6e93d96aef 100644
> --- a/libavformat/vividas.c
> +++ b/libavformat/vividas.c
> @@ -682,7 +682,7 @@ static int viv_read_packet(AVFormatContext *s,
>              return AVERROR_INVALIDDATA;
>  
>          ffio_read_varlen(pb);
> -        if (v_size > INT_MAX)
> +        if (v_size > INT_MAX || !v_size)
>              return AVERROR_INVALIDDATA;
>          ret = av_get_packet(pb, pkt, v_size);
>          if (ret < 0)
> @@ -711,7 +711,7 @@ static int viv_read_packet(AVFormatContext *s,
>      } else {
>          uint64_t v_size = ffio_read_varlen(pb);
>  
> -        if (v_size > INT_MAX)
> +        if (v_size > INT_MAX || !v_size)
>              return AVERROR_INVALIDDATA;
>          ret = av_get_packet(pb, pkt, v_size);
>          if (ret < 0)
> 
av_get_packet(pb, pkt, 0) should get a packet with pkt->data pointing to
a zeroed buffer of size AV_INPUT_BUFFER_PADDING_SIZE. So accessing
pkt->data[0] for the flags should not segfault (but it would set the
wrong result: that it is a keyframe). So where is the segfault?

- Andreas
Michael Niedermayer Oct. 22, 2020, 4:36 p.m. UTC | #2
On Thu, Oct 22, 2020 at 07:55:31AM +0200, Andreas Rheinhardt wrote:
> Michael Niedermayer:
> > Fixes: SEGV on unknown address 0x000000000000
> > Fixes: 26482/clusterfuzz-testcase-minimized-ffmpeg_dem_VIVIDAS_fuzzer-4905102324006912
> > 
> > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > ---
> >  libavformat/vividas.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/libavformat/vividas.c b/libavformat/vividas.c
> > index 999c4a5d1c..6e93d96aef 100644
> > --- a/libavformat/vividas.c
> > +++ b/libavformat/vividas.c
> > @@ -682,7 +682,7 @@ static int viv_read_packet(AVFormatContext *s,
> >              return AVERROR_INVALIDDATA;
> >  
> >          ffio_read_varlen(pb);
> > -        if (v_size > INT_MAX)
> > +        if (v_size > INT_MAX || !v_size)
> >              return AVERROR_INVALIDDATA;
> >          ret = av_get_packet(pb, pkt, v_size);
> >          if (ret < 0)
> > @@ -711,7 +711,7 @@ static int viv_read_packet(AVFormatContext *s,
> >      } else {
> >          uint64_t v_size = ffio_read_varlen(pb);
> >  
> > -        if (v_size > INT_MAX)
> > +        if (v_size > INT_MAX || !v_size)
> >              return AVERROR_INVALIDDATA;
> >          ret = av_get_packet(pb, pkt, v_size);
> >          if (ret < 0)
> > 
> av_get_packet(pb, pkt, 0) should get a packet with pkt->data pointing to
> a zeroed buffer of size AV_INPUT_BUFFER_PADDING_SIZE. So accessing
> pkt->data[0] for the flags should not segfault (but it would set the
> wrong result: that it is a keyframe). So where is the segfault?

I tried to simulate this in a different demuxer:
(different to make sure its not the file or demuxer that somehow affects this)
--- a/libavformat/avidec.c
+++ b/libavformat/avidec.c
@@ -1446,9 +1446,10 @@ resync:
         if (size > ast->remaining)
             size = ast->remaining;
         avi->last_pkt_pos = avio_tell(pb);
-        err               = av_get_packet(pb, pkt, size);
+        err               = av_get_packet(pb, pkt, 0);
         if (err < 0)
             return err;
+        av_log(0,0, "P %p\n", pkt->data);
         size = err;
 
         if (ast->has_pal && pkt->size < (unsigned)INT_MAX / 2) {

what is printed is:
P (nil)

[...]
Andreas Rheinhardt Oct. 22, 2020, 4:55 p.m. UTC | #3
Michael Niedermayer:
> On Thu, Oct 22, 2020 at 07:55:31AM +0200, Andreas Rheinhardt wrote:
>> Michael Niedermayer:
>>> Fixes: SEGV on unknown address 0x000000000000
>>> Fixes: 26482/clusterfuzz-testcase-minimized-ffmpeg_dem_VIVIDAS_fuzzer-4905102324006912
>>>
>>> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
>>> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
>>> ---
>>>  libavformat/vividas.c | 4 ++--
>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/libavformat/vividas.c b/libavformat/vividas.c
>>> index 999c4a5d1c..6e93d96aef 100644
>>> --- a/libavformat/vividas.c
>>> +++ b/libavformat/vividas.c
>>> @@ -682,7 +682,7 @@ static int viv_read_packet(AVFormatContext *s,
>>>              return AVERROR_INVALIDDATA;
>>>  
>>>          ffio_read_varlen(pb);
>>> -        if (v_size > INT_MAX)
>>> +        if (v_size > INT_MAX || !v_size)
>>>              return AVERROR_INVALIDDATA;
>>>          ret = av_get_packet(pb, pkt, v_size);
>>>          if (ret < 0)
>>> @@ -711,7 +711,7 @@ static int viv_read_packet(AVFormatContext *s,
>>>      } else {
>>>          uint64_t v_size = ffio_read_varlen(pb);
>>>  
>>> -        if (v_size > INT_MAX)
>>> +        if (v_size > INT_MAX || !v_size)
>>>              return AVERROR_INVALIDDATA;
>>>          ret = av_get_packet(pb, pkt, v_size);
>>>          if (ret < 0)
>>>
>> av_get_packet(pb, pkt, 0) should get a packet with pkt->data pointing to
>> a zeroed buffer of size AV_INPUT_BUFFER_PADDING_SIZE. So accessing
>> pkt->data[0] for the flags should not segfault (but it would set the
>> wrong result: that it is a keyframe). So where is the segfault?
> 
> I tried to simulate this in a different demuxer:
> (different to make sure its not the file or demuxer that somehow affects this)
> --- a/libavformat/avidec.c
> +++ b/libavformat/avidec.c
> @@ -1446,9 +1446,10 @@ resync:
>          if (size > ast->remaining)
>              size = ast->remaining;
>          avi->last_pkt_pos = avio_tell(pb);
> -        err               = av_get_packet(pb, pkt, size);
> +        err               = av_get_packet(pb, pkt, 0);
>          if (err < 0)
>              return err;
> +        av_log(0,0, "P %p\n", pkt->data);
>          size = err;
>  
>          if (ast->has_pal && pkt->size < (unsigned)INT_MAX / 2) {
> 
> what is printed is:
> P (nil)
> 
My bad: append_packet_chunked() unrefs the packet if pkt->size is zero
before returning (without returning an error). So your patch seems to be
the way to go.

- Andreas
Michael Niedermayer Oct. 23, 2020, 7:47 a.m. UTC | #4
On Thu, Oct 22, 2020 at 06:55:37PM +0200, Andreas Rheinhardt wrote:
> Michael Niedermayer:
> > On Thu, Oct 22, 2020 at 07:55:31AM +0200, Andreas Rheinhardt wrote:
> >> Michael Niedermayer:
> >>> Fixes: SEGV on unknown address 0x000000000000
> >>> Fixes: 26482/clusterfuzz-testcase-minimized-ffmpeg_dem_VIVIDAS_fuzzer-4905102324006912
> >>>
> >>> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> >>> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> >>> ---
> >>>  libavformat/vividas.c | 4 ++--
> >>>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/libavformat/vividas.c b/libavformat/vividas.c
> >>> index 999c4a5d1c..6e93d96aef 100644
> >>> --- a/libavformat/vividas.c
> >>> +++ b/libavformat/vividas.c
> >>> @@ -682,7 +682,7 @@ static int viv_read_packet(AVFormatContext *s,
> >>>              return AVERROR_INVALIDDATA;
> >>>  
> >>>          ffio_read_varlen(pb);
> >>> -        if (v_size > INT_MAX)
> >>> +        if (v_size > INT_MAX || !v_size)
> >>>              return AVERROR_INVALIDDATA;
> >>>          ret = av_get_packet(pb, pkt, v_size);
> >>>          if (ret < 0)
> >>> @@ -711,7 +711,7 @@ static int viv_read_packet(AVFormatContext *s,
> >>>      } else {
> >>>          uint64_t v_size = ffio_read_varlen(pb);
> >>>  
> >>> -        if (v_size > INT_MAX)
> >>> +        if (v_size > INT_MAX || !v_size)
> >>>              return AVERROR_INVALIDDATA;
> >>>          ret = av_get_packet(pb, pkt, v_size);
> >>>          if (ret < 0)
> >>>
> >> av_get_packet(pb, pkt, 0) should get a packet with pkt->data pointing to
> >> a zeroed buffer of size AV_INPUT_BUFFER_PADDING_SIZE. So accessing
> >> pkt->data[0] for the flags should not segfault (but it would set the
> >> wrong result: that it is a keyframe). So where is the segfault?
> > 
> > I tried to simulate this in a different demuxer:
> > (different to make sure its not the file or demuxer that somehow affects this)
> > --- a/libavformat/avidec.c
> > +++ b/libavformat/avidec.c
> > @@ -1446,9 +1446,10 @@ resync:
> >          if (size > ast->remaining)
> >              size = ast->remaining;
> >          avi->last_pkt_pos = avio_tell(pb);
> > -        err               = av_get_packet(pb, pkt, size);
> > +        err               = av_get_packet(pb, pkt, 0);
> >          if (err < 0)
> >              return err;
> > +        av_log(0,0, "P %p\n", pkt->data);
> >          size = err;
> >  
> >          if (ast->has_pal && pkt->size < (unsigned)INT_MAX / 2) {
> > 
> > what is printed is:
> > P (nil)
> > 
> My bad: append_packet_chunked() unrefs the packet if pkt->size is zero
> before returning (without returning an error). So your patch seems to be
> the way to go.

ok, will apply

thx

[...]
diff mbox series

Patch

diff --git a/libavformat/vividas.c b/libavformat/vividas.c
index 999c4a5d1c..6e93d96aef 100644
--- a/libavformat/vividas.c
+++ b/libavformat/vividas.c
@@ -682,7 +682,7 @@  static int viv_read_packet(AVFormatContext *s,
             return AVERROR_INVALIDDATA;
 
         ffio_read_varlen(pb);
-        if (v_size > INT_MAX)
+        if (v_size > INT_MAX || !v_size)
             return AVERROR_INVALIDDATA;
         ret = av_get_packet(pb, pkt, v_size);
         if (ret < 0)
@@ -711,7 +711,7 @@  static int viv_read_packet(AVFormatContext *s,
     } else {
         uint64_t v_size = ffio_read_varlen(pb);
 
-        if (v_size > INT_MAX)
+        if (v_size > INT_MAX || !v_size)
             return AVERROR_INVALIDDATA;
         ret = av_get_packet(pb, pkt, v_size);
         if (ret < 0)