Re: [FFmpeg-devel] [PATCH 2/2] avcodec/h2645_parse: Check HEVC NAL size

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Michael Niedermayer:
> Fixes: Assertion failure
> Fixes: 46662/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_HEVC_fuzzer-4947860854013952
> 
> This also results in more frames to be decoded from fate samples
> 
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavcodec/h2645_parse.c                               |  2 +-
>  .../ref/fate/hevc-conformance-NoOutPrior_A_Qualcomm_1  | 10 ++++++++++
>  tests/ref/fate/hevc-conformance-RAP_B_Bossen_1         |  3 +++
>  3 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/h2645_parse.c b/libavcodec/h2645_parse.c
> index 03780680c6..78ab22b76e 100644
> --- a/libavcodec/h2645_parse.c
> +++ b/libavcodec/h2645_parse.c
> @@ -292,7 +292,7 @@ static int hevc_parse_nal_header(H2645NAL *nal, void *logctx)
>  {
>      GetBitContext *gb = &nal->gb;
>  
> -    if (get_bits1(gb) != 0)
> +    if (get_bits_left(gb) < 16 || get_bits1(gb) != 0)
>          return AVERROR_INVALIDDATA;
>  
>      nal->type = get_bits(gb, 6);
> diff --git a/tests/ref/fate/hevc-conformance-NoOutPrior_A_Qualcomm_1 b/tests/ref/fate/hevc-conformance-NoOutPrior_A_Qualcomm_1
> index 0c930f6556..3283925e38 100644
> --- a/tests/ref/fate/hevc-conformance-NoOutPrior_A_Qualcomm_1
> +++ b/tests/ref/fate/hevc-conformance-NoOutPrior_A_Qualcomm_1
> @@ -25,6 +25,16 @@
>  0,         19,         19,        1,   599040, 0x4227009b
>  0,         20,         20,        1,   599040, 0x1bda8be4
>  0,         21,         21,        1,   599040, 0xd1d5dcb4
> +0,         22,         22,        1,   599040, 0x58b2edb3
> +0,         23,         23,        1,   599040, 0xd1f795d8
> +0,         24,         24,        1,   599040, 0x3331d5e6
> +0,         25,         25,        1,   599040, 0x5e5ec2c9
> +0,         26,         26,        1,   599040, 0x3b907bf5
> +0,         27,         27,        1,   599040, 0xefcbf471
> +0,         28,         28,        1,   599040, 0x2769a578
> +0,         29,         29,        1,   599040, 0x812ce986
> +0,         30,         30,        1,   599040, 0xf07c212c
> +0,         31,         31,        1,   599040, 0xb5476890
>  0,         32,         32,        1,   599040, 0x00a0249f
>  0,         33,         33,        1,   599040, 0x7263f7cf
>  0,         34,         34,        1,   599040, 0x47054be4
> diff --git a/tests/ref/fate/hevc-conformance-RAP_B_Bossen_1 b/tests/ref/fate/hevc-conformance-RAP_B_Bossen_1
> index e661ff245e..776267b59c 100644
> --- a/tests/ref/fate/hevc-conformance-RAP_B_Bossen_1
> +++ b/tests/ref/fate/hevc-conformance-RAP_B_Bossen_1
> @@ -70,6 +70,9 @@
>  0,         64,         64,        1,   149760, 0x3362678b
>  0,         65,         65,        1,   149760, 0x6e7fc851
>  0,         66,         66,        1,   149760, 0x33f96449
> +0,         67,         67,        1,   149760, 0xd9d05007
> +0,         75,         75,        1,   149760, 0x477f2cf2
> +0,         76,         76,        1,   149760, 0xe1f9ccd0
>  0,         77,         77,        1,   149760, 0xb3ba8cfb
>  0,         78,         78,        1,   149760, 0x64787995
>  0,         79,         79,        1,   149760, 0xc10de4c4

get_bit_length currently presumes every NALU to contain
rbsp_trailing_bits. Yet this is not true for the End of
Sequence/Bitstream units which are just headers without RBSP. For these
units, get_bit_length might truncate them -- it does so for end of
sequence units in H.264. It would not be a serious issue for H.265, as
the semantics of nuh_temporal_id_plus1 require nuh_temporal_id_plus1 to
be 1 for End of Sequence/Bitstream units. Nevertheless I think this
should be coupled with a patch that does not truncate the NAL unit if it
is just a header.

- Andreas
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