On Mon, Oct 05, 2020 at 01:30:07AM -0300, James Almer wrote: > On 10/4/2020 6:02 PM, James Almer wrote: > > On 10/4/2020 5:57 PM, Michael Niedermayer wrote: > >> On Sun, Oct 04, 2020 at 05:04:05PM -0300, James Almer wrote: > >>> On 10/4/2020 4:41 PM, Michael Niedermayer wrote: > >>>> Fixes: OOM > >>>> Fixes: > >>>> 23817/clusterfuzz-testcase-minimized-ffmpeg_BSF_H264_METADATA_fuzzer-6300869057576960 > >>>> > >>>> Found-by: continuous fuzzing process > >>>> https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg > >>>> Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc> > >>>> --- > >>>> libavcodec/h2645_parse.c | 2 +- > >>>> 1 file changed, 1 insertion(+), 1 deletion(-) > >>>> > >>>> diff --git a/libavcodec/h2645_parse.c b/libavcodec/h2645_parse.c > >>>> index 0f98b49fbe..61105a6eb5 100644 > >>>> --- a/libavcodec/h2645_parse.c > >>>> +++ b/libavcodec/h2645_parse.c > >>>> @@ -467,7 +467,7 @@ int ff_h2645_packet_split(H2645Packet *pkt, const > >>>> uint8_t *buf, int length, > >>>> memset(pkt->nals + pkt->nals_allocated, 0, > >>>> sizeof(*pkt->nals)); > >>>> > >>>> nal = &pkt->nals[pkt->nb_nals]; > >>>> - nal->skipped_bytes_pos_size = 1024; // initial buffer size > >>>> + nal->skipped_bytes_pos_size = FFMIN(1024, > >>>> 1+(extract_length>>4)); // initial buffer size > >>> > >>> Why is there even an initial buffer? Why not just let > >>> ff_h2645_extract_rbsp() allocate it when needed? > >> > >> i wondered that too and assumed it was done that way to avoid spending > >> cpu cycles on reallocations later > > > > Many streams don't need to escape bytes, so for those, allocating > > anything at all is a waste. And IMO by using av_fast_realloc() in > > ff_h2645_extract_rbsp() there's no need for a big enough initial buffer > > either. > > On second thought, even if most av_fast_realloc() calls will be no-ops, > they may end up being way too many to the point the current behavior > would be more efficient. > > Does moving the allocation of the initial buffer to > ff_h2645_extract_rbsp() also help with this sample? I assume it's one > where it generates an absurd amount of NAL units in the packet, but most > would probably be small enough that they will not really contain bytes > that need to be escaped, and as such not require a skipped_bytes_pos buffer.
your variant below works too, yes the fuzzer testcase is a gazzilion of 1byte NAL units IIRC thx [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB No great genius has ever existed without some touch of madness. -- Aristotle
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