Re: [FFmpeg-devel] [PATCH 3/3] avformat/mxfdec: Reduce overflows in essence_length computation
On Fri, Dec 23, 2022 at 12:47:02PM +0100, Tomas Härdin wrote:
> fre 2022-12-23 klockan 00:25 +0100 skrev Michael Niedermayer:
> > On Wed, Nov 16, 2022 at 12:49:10PM +0100, Tomas Härdin wrote:
> > > sön 2022-11-13 klockan 00:44 +0100 skrev Michael Niedermayer:
> > > > Fixes: signed integer overflow: -3741319169 - 9223372036823449370
> > > > cannot be represented in type 'long'
> > > > Fixes: 51896/clusterfuzz-testcase-minimized-
> > > > ffmpeg_dem_MXF_fuzzer-
> > > > 513039428681728
> > > >
> > > > Found-by: continuous fuzzing process
> > > > https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > > > Signed-off-by: Michael Niedermayer
> > > > ---
> > > > libavformat/mxfdec.c | 10 +++---
> > > > 1 file changed, 7 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/libavformat/mxfdec.c b/libavformat/mxfdec.c
> > > > index e6118e141d..42109cb43a 100644
> > > > --- a/libavformat/mxfdec.c
> > > > +++ b/libavformat/mxfdec.c
> > > > @@ -100,7 +100,7 @@ typedef struct MXFPartition {
> > > > uint64_t previous_partition;
> > > > int index_sid;
> > > > int body_sid;
> > > > - int64_t this_partition;
> > > > + uint64_t this_partition;
> > > > int64_t essence_offset; ///< absolute offset of
> > > > essence
> > > > int64_t essence_length;
> > > > int32_t kag_size;
> > > > @@ -3519,8 +3519,12 @@ static void
> > > > mxf_compute_essence_containers(AVFormatContext *s)
> > > > p->essence_offset = p->first_essence_klv.offset;
> > > >
> > > > /* essence container spans to the next partition */
> > > > - if (x < mxf->partitions_count - 1)
> > > > - p->essence_length = mxf-
> > > > > partitions[x+1].this_partition - p->essence_offset;
> > > > + if (x < mxf->partitions_count - 1) {
> > > > + if (mxf->partitions[x+1].this_partition < p-
> > > > > essence_offset) {
> > > > + p->essence_length = -1;
> > > > + } else
> > > > + p->essence_length = mxf-
> > > > > partitions[x+1].this_partition - p->essence_offset;
> > > > + }
> > >
> > > A better solution might be to record the actual offset of the
> > > partitions rather than relying on ThisPartition. Then we can
> > > guarantee
> > > that they are strictly increasing.
> >
> > do you mean that pack_ofs could be used here ?
>
> this_partition should be == pack_ofs - run_in. I think we can just nuke
> this_partition in the struct and use pack_ofs - run_in everywhere. Emit
> a warning or bail out if any partition does not obey this contraint,
> since such files have likely been written by bad muxers.
ill post a patch doing that
thx
[...]
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Re: [FFmpeg-devel] [PATCH 3/3] avformat/mxfdec: Reduce overflows in essence_length computation
fre 2022-12-23 klockan 00:25 +0100 skrev Michael Niedermayer:
> On Wed, Nov 16, 2022 at 12:49:10PM +0100, Tomas Härdin wrote:
> > sön 2022-11-13 klockan 00:44 +0100 skrev Michael Niedermayer:
> > > Fixes: signed integer overflow: -3741319169 - 9223372036823449370
> > > cannot be represented in type 'long'
> > > Fixes: 51896/clusterfuzz-testcase-minimized-
> > > ffmpeg_dem_MXF_fuzzer-
> > > 513039428681728
> > >
> > > Found-by: continuous fuzzing process
> > > https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > > Signed-off-by: Michael Niedermayer
> > > ---
> > > libavformat/mxfdec.c | 10 +++---
> > > 1 file changed, 7 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/libavformat/mxfdec.c b/libavformat/mxfdec.c
> > > index e6118e141d..42109cb43a 100644
> > > --- a/libavformat/mxfdec.c
> > > +++ b/libavformat/mxfdec.c
> > > @@ -100,7 +100,7 @@ typedef struct MXFPartition {
> > > uint64_t previous_partition;
> > > int index_sid;
> > > int body_sid;
> > > - int64_t this_partition;
> > > + uint64_t this_partition;
> > > int64_t essence_offset; ///< absolute offset of
> > > essence
> > > int64_t essence_length;
> > > int32_t kag_size;
> > > @@ -3519,8 +3519,12 @@ static void
> > > mxf_compute_essence_containers(AVFormatContext *s)
> > > p->essence_offset = p->first_essence_klv.offset;
> > >
> > > /* essence container spans to the next partition */
> > > - if (x < mxf->partitions_count - 1)
> > > - p->essence_length = mxf-
> > > > partitions[x+1].this_partition - p->essence_offset;
> > > + if (x < mxf->partitions_count - 1) {
> > > + if (mxf->partitions[x+1].this_partition < p-
> > > > essence_offset) {
> > > + p->essence_length = -1;
> > > + } else
> > > + p->essence_length = mxf-
> > > > partitions[x+1].this_partition - p->essence_offset;
> > > + }
> >
> > A better solution might be to record the actual offset of the
> > partitions rather than relying on ThisPartition. Then we can
> > guarantee
> > that they are strictly increasing.
>
> do you mean that pack_ofs could be used here ?
this_partition should be == pack_ofs - run_in. I think we can just nuke
this_partition in the struct and use pack_ofs - run_in everywhere. Emit
a warning or bail out if any partition does not obey this contraint,
since such files have likely been written by bad muxers.
> but as pack_ofs is signed that either means dealing with potentially
> negative
> or changing it to uint64_t or adding a new field and avio_tell()
> somewhere?
pack_ofs can only be negative in case of error, in which case we should
bail out anyway. Something must be very wrong if lavf can't avio_tell()
For every partition, pack_ofs >= run_in. this_partition >= 0, and in
particular this_partition == 0 for the very first partition.
This is reminding me that I had some finer points to fix related to
run_in and deleting the superfluous sync stuff that's currently in the
code. Baptiste is fine with that, as it's a relic from when mxfdec
didn't have proper seek support.
/Tomas
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Re: [FFmpeg-devel] [PATCH 3/3] avformat/mxfdec: Reduce overflows in essence_length computation
On Wed, Nov 16, 2022 at 12:49:10PM +0100, Tomas Härdin wrote:
> sön 2022-11-13 klockan 00:44 +0100 skrev Michael Niedermayer:
> > Fixes: signed integer overflow: -3741319169 - 9223372036823449370
> > cannot be represented in type 'long'
> > Fixes: 51896/clusterfuzz-testcase-minimized-ffmpeg_dem_MXF_fuzzer-
> > 513039428681728
> >
> > Found-by: continuous fuzzing process
> > https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer
> > ---
> > libavformat/mxfdec.c | 10 +++---
> > 1 file changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/libavformat/mxfdec.c b/libavformat/mxfdec.c
> > index e6118e141d..42109cb43a 100644
> > --- a/libavformat/mxfdec.c
> > +++ b/libavformat/mxfdec.c
> > @@ -100,7 +100,7 @@ typedef struct MXFPartition {
> > uint64_t previous_partition;
> > int index_sid;
> > int body_sid;
> > - int64_t this_partition;
> > + uint64_t this_partition;
> > int64_t essence_offset; ///< absolute offset of essence
> > int64_t essence_length;
> > int32_t kag_size;
> > @@ -3519,8 +3519,12 @@ static void
> > mxf_compute_essence_containers(AVFormatContext *s)
> > p->essence_offset = p->first_essence_klv.offset;
> >
> > /* essence container spans to the next partition */
> > - if (x < mxf->partitions_count - 1)
> > - p->essence_length = mxf-
> > >partitions[x+1].this_partition - p->essence_offset;
> > + if (x < mxf->partitions_count - 1) {
> > + if (mxf->partitions[x+1].this_partition < p-
> > >essence_offset) {
> > + p->essence_length = -1;
> > + } else
> > + p->essence_length = mxf-
> > >partitions[x+1].this_partition - p->essence_offset;
> > + }
>
> A better solution might be to record the actual offset of the
> partitions rather than relying on ThisPartition. Then we can guarantee
> that they are strictly increasing.
do you mean that pack_ofs could be used here ?
(this is within 8 byte of this_partition) for the files i checked
or something else ?
but as pack_ofs is signed that either means dealing with potentially negative
or changing it to uint64_t or adding a new field and avio_tell() somewhere?
thx
[...]
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Re: [FFmpeg-devel] [PATCH 3/3] avformat/mxfdec: Reduce overflows in essence_length computation
sön 2022-11-13 klockan 00:44 +0100 skrev Michael Niedermayer:
> Fixes: signed integer overflow: -3741319169 - 9223372036823449370
> cannot be represented in type 'long'
> Fixes: 51896/clusterfuzz-testcase-minimized-ffmpeg_dem_MXF_fuzzer-
> 513039428681728
>
> Found-by: continuous fuzzing process
> https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer
> ---
> libavformat/mxfdec.c | 10 +++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/libavformat/mxfdec.c b/libavformat/mxfdec.c
> index e6118e141d..42109cb43a 100644
> --- a/libavformat/mxfdec.c
> +++ b/libavformat/mxfdec.c
> @@ -100,7 +100,7 @@ typedef struct MXFPartition {
> uint64_t previous_partition;
> int index_sid;
> int body_sid;
> - int64_t this_partition;
> + uint64_t this_partition;
> int64_t essence_offset; ///< absolute offset of essence
> int64_t essence_length;
> int32_t kag_size;
> @@ -3519,8 +3519,12 @@ static void
> mxf_compute_essence_containers(AVFormatContext *s)
> p->essence_offset = p->first_essence_klv.offset;
>
> /* essence container spans to the next partition */
> - if (x < mxf->partitions_count - 1)
> - p->essence_length = mxf-
> >partitions[x+1].this_partition - p->essence_offset;
> + if (x < mxf->partitions_count - 1) {
> + if (mxf->partitions[x+1].this_partition < p-
> >essence_offset) {
> + p->essence_length = -1;
> + } else
> + p->essence_length = mxf-
> >partitions[x+1].this_partition - p->essence_offset;
> + }
A better solution might be to record the actual offset of the
partitions rather than relying on ThisPartition. Then we can guarantee
that they are strictly increasing.
/Tomas
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