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[FFmpeg-devel,1/4] avformat/avidec: Check for dv streams before using priv_data in parse ##dc/##wb

Message ID 20210318204958.21176-1-michael@niedermayer.cc
State Accepted
Commit f733688d30021587c3f3a1b280d6ece8b04f26ff
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Series [FFmpeg-devel,1/4] avformat/avidec: Check for dv streams before using priv_data in parse ##dc/##wb
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Commit Message

Michael Niedermayer March 18, 2021, 8:49 p.m. UTC
Fixes: null pointer dereference
Fixes: 31588/clusterfuzz-testcase-minimized-ffmpeg_dem_AVI_fuzzer-6165716135968768

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

Comments

Andreas Rheinhardt March 18, 2021, 11:20 p.m. UTC | #1
Michael Niedermayer:
> Fixes: null pointer dereference
> Fixes: 31588/clusterfuzz-testcase-minimized-ffmpeg_dem_AVI_fuzzer-6165716135968768
> 
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavformat/avidec.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavformat/avidec.c b/libavformat/avidec.c
> index fa0599501a..48370fe5ce 100644
> --- a/libavformat/avidec.c
> +++ b/libavformat/avidec.c
> @@ -1288,7 +1288,7 @@ start_sync:
>                  AVStream *st1   = s->streams[1];
>                  AVIStream *ast1 = st1->priv_data;
>                  // workaround for broken small-file-bug402.avi
> -                if (   d[2] == 'w' && d[3] == 'b'
> +                if (ast1 && d[2] == 'w' && d[3] == 'b'
>                     && n == 0
>                     && st ->codecpar->codec_type == AVMEDIA_TYPE_VIDEO
>                     && st1->codecpar->codec_type == AVMEDIA_TYPE_AUDIO
> 
How is this possible? After all, dv streams also have an AVIStream as
priv_data; and only the very first stream can ever be a dv stream due to
the check in line 605.

- Andreas
Michael Niedermayer March 18, 2021, 11:54 p.m. UTC | #2
On Fri, Mar 19, 2021 at 12:20:23AM +0100, Andreas Rheinhardt wrote:
> Michael Niedermayer:
> > Fixes: null pointer dereference
> > Fixes: 31588/clusterfuzz-testcase-minimized-ffmpeg_dem_AVI_fuzzer-6165716135968768
> > 
> > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > ---
> >  libavformat/avidec.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/libavformat/avidec.c b/libavformat/avidec.c
> > index fa0599501a..48370fe5ce 100644
> > --- a/libavformat/avidec.c
> > +++ b/libavformat/avidec.c
> > @@ -1288,7 +1288,7 @@ start_sync:
> >                  AVStream *st1   = s->streams[1];
> >                  AVIStream *ast1 = st1->priv_data;
> >                  // workaround for broken small-file-bug402.avi
> > -                if (   d[2] == 'w' && d[3] == 'b'
> > +                if (ast1 && d[2] == 'w' && d[3] == 'b'
> >                     && n == 0
> >                     && st ->codecpar->codec_type == AVMEDIA_TYPE_VIDEO
> >                     && st1->codecpar->codec_type == AVMEDIA_TYPE_AUDIO
> > 
> How is this possible? After all, dv streams also have an AVIStream as

The DV demuxer creates streams in dv_extract_audio_info() without a AVIStream


> priv_data; and only the very first stream can ever be a dv stream due to
> the check in line 605.

I assume they are created after that check



[...]
Andreas Rheinhardt March 19, 2021, 12:19 a.m. UTC | #3
Michael Niedermayer:
> On Fri, Mar 19, 2021 at 12:20:23AM +0100, Andreas Rheinhardt wrote:
>> Michael Niedermayer:
>>> Fixes: null pointer dereference
>>> Fixes: 31588/clusterfuzz-testcase-minimized-ffmpeg_dem_AVI_fuzzer-6165716135968768
>>>
>>> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
>>> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
>>> ---
>>>  libavformat/avidec.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/libavformat/avidec.c b/libavformat/avidec.c
>>> index fa0599501a..48370fe5ce 100644
>>> --- a/libavformat/avidec.c
>>> +++ b/libavformat/avidec.c
>>> @@ -1288,7 +1288,7 @@ start_sync:
>>>                  AVStream *st1   = s->streams[1];
>>>                  AVIStream *ast1 = st1->priv_data;
>>>                  // workaround for broken small-file-bug402.avi
>>> -                if (   d[2] == 'w' && d[3] == 'b'
>>> +                if (ast1 && d[2] == 'w' && d[3] == 'b'
>>>                     && n == 0
>>>                     && st ->codecpar->codec_type == AVMEDIA_TYPE_VIDEO
>>>                     && st1->codecpar->codec_type == AVMEDIA_TYPE_AUDIO
>>>
>> How is this possible? After all, dv streams also have an AVIStream as
> 
> The DV demuxer creates streams in dv_extract_audio_info() without a AVIStream
> 

That explains it. Thanks. Patch is fine by me, but I haven't looked at
it in detail. But neither dv nor avi set the AVFMTCTX_NOHEADER flag, so
adding streams later is an API violation.

> 
>> priv_data; and only the very first stream can ever be a dv stream due to
>> the check in line 605.
> 
> I assume they are created after that check
> 
>
Michael Niedermayer March 25, 2021, 5:12 p.m. UTC | #4
On Fri, Mar 19, 2021 at 01:19:28AM +0100, Andreas Rheinhardt wrote:
> Michael Niedermayer:
> > On Fri, Mar 19, 2021 at 12:20:23AM +0100, Andreas Rheinhardt wrote:
> >> Michael Niedermayer:
> >>> Fixes: null pointer dereference
> >>> Fixes: 31588/clusterfuzz-testcase-minimized-ffmpeg_dem_AVI_fuzzer-6165716135968768
> >>>
> >>> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> >>> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> >>> ---
> >>>  libavformat/avidec.c | 2 +-
> >>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/libavformat/avidec.c b/libavformat/avidec.c
> >>> index fa0599501a..48370fe5ce 100644
> >>> --- a/libavformat/avidec.c
> >>> +++ b/libavformat/avidec.c
> >>> @@ -1288,7 +1288,7 @@ start_sync:
> >>>                  AVStream *st1   = s->streams[1];
> >>>                  AVIStream *ast1 = st1->priv_data;
> >>>                  // workaround for broken small-file-bug402.avi
> >>> -                if (   d[2] == 'w' && d[3] == 'b'
> >>> +                if (ast1 && d[2] == 'w' && d[3] == 'b'
> >>>                     && n == 0
> >>>                     && st ->codecpar->codec_type == AVMEDIA_TYPE_VIDEO
> >>>                     && st1->codecpar->codec_type == AVMEDIA_TYPE_AUDIO
> >>>
> >> How is this possible? After all, dv streams also have an AVIStream as
> > 
> > The DV demuxer creates streams in dv_extract_audio_info() without a AVIStream
> > 
> 
> That explains it. Thanks. Patch is fine by me, 

will apply

thx


> but I haven't looked at
> it in detail. But neither dv nor avi set the AVFMTCTX_NOHEADER flag, so
> adding streams later is an API violation.
> 
> > 
> >> priv_data; and only the very first stream can ever be a dv stream due to
> >> the check in line 605.
> > 
> > I assume they are created after that check
> > 
> > 
> 
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diff mbox series

Patch

diff --git a/libavformat/avidec.c b/libavformat/avidec.c
index fa0599501a..48370fe5ce 100644
--- a/libavformat/avidec.c
+++ b/libavformat/avidec.c
@@ -1288,7 +1288,7 @@  start_sync:
                 AVStream *st1   = s->streams[1];
                 AVIStream *ast1 = st1->priv_data;
                 // workaround for broken small-file-bug402.avi
-                if (   d[2] == 'w' && d[3] == 'b'
+                if (ast1 && d[2] == 'w' && d[3] == 'b'
                    && n == 0
                    && st ->codecpar->codec_type == AVMEDIA_TYPE_VIDEO
                    && st1->codecpar->codec_type == AVMEDIA_TYPE_AUDIO