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 <mich...@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)
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
Asymptotically faster algorithms should always be preferred if you have
asymptotical amounts of data
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