On Fri, Jan 22, 2021 at 11:23:09AM -0300, James Almer wrote: > On 1/22/2021 11:09 AM, Michael Niedermayer wrote: > > Fixes: signed integer overflow: 9223372036854775723 + 8192 cannot be > > represented in type 'long' > > Fixes: > > 29072/clusterfuzz-testcase-minimized-ffmpeg_dem_MXF_fuzzer-4812604904177664 > > > > Found-by: continuous fuzzing process > > https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg > > Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc> > > --- > > libavformat/mxfdec.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/libavformat/mxfdec.c b/libavformat/mxfdec.c > > index 4c932e954c..f1167761f9 100644 > > --- a/libavformat/mxfdec.c > > +++ b/libavformat/mxfdec.c > > @@ -2865,8 +2865,10 @@ static int mxf_read_local_tags(MXFContext *mxf, > > KLVPacket *klv, MXFMetadataReadF > > int ret; > > int tag = avio_rb16(pb); > > int size = avio_rb16(pb); /* KLV specified by 0x53 */ > > - uint64_t next = avio_tell(pb) + size; > > + uint64_t next = avio_tell(pb); > > UID uid = {0}; > > + if (next > INT64_MAX - size) > > + size = 0; > > You're discarding the tag's size. The code below could misbehave as it will > assume it's an empty tag when it's not. Not to mention the log message will > print a bogus value. > > Abort instead (Invalid data or erange) in this scenario since going beyond > INT64_MAX is clearly not supported by avio, and then do next += size to > ensure the avio_seek() at the end works as expected.
I dont think this strictly implies being beyond INT64_MAX.
but i wanted to redo this patch anyway as it contained another bug
so next suggestion:
@@ -2865,8 +2865,11 @@ static int mxf_read_local_tags(MXFContext *mxf,
KLVPacket *klv, MXFMetadataReadF
int ret;
int tag = avio_rb16(pb);
int size = avio_rb16(pb); /* KLV specified by 0x53 */
- uint64_t next = avio_tell(pb) + size;
+ int64_t next = avio_tell(pb);
UID uid = {0};
+ if (next < 0 || next > INT64_MAX - size)
+ return next < 0 ? next : AVERROR_INVALIDDATA;
+ next += size;
av_log(mxf->fc, AV_LOG_TRACE, "local tag %#04x size %d\n", tag, size);
if (!size) { /* ignore empty tag, needed for some files with empty
UMID tag */
thx
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
Breaking DRM is a little like attempting to break through a door even
though the window is wide open and the only thing in the house is a bunch
of things you dont want and which you would get tomorrow for free anyway
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