Re: [FFmpeg-devel] [PATCH 1/5] avcodec/aac/aacdec_usac: Test ac in usac

[Michael Niedermayer <michael@niedermayer.cc>]

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On Wed, Jun 26, 2024 at 01:35:18AM +0200, Lynne via ffmpeg-devel wrote:
> On 24/06/2024 01:01, Michael Niedermayer wrote:
> > ff_aac_usac_config_decode() needs AACDecContext to be set but some callers
> > pass NULL.
> > 
> > I have no real testcase to implement/test this, so failing in this case
> > seems safest.
> > 
> > Fixes: member access within null pointer of type 'AACDecContext' (aka 'struct AACDecContext')
> > Fixes: 69435/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_AAC_LATM_fuzzer-5733527483121664
> > 
> > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > ---
> >   libavcodec/aac/aacdec_usac.c | 3 +++
> >   1 file changed, 3 insertions(+)
> > 
> > diff --git a/libavcodec/aac/aacdec_usac.c b/libavcodec/aac/aacdec_usac.c
> > index 132ffee9c20..4856c1786b7 100644
> > --- a/libavcodec/aac/aacdec_usac.c
> > +++ b/libavcodec/aac/aacdec_usac.c
> > @@ -348,6 +348,9 @@ int ff_aac_usac_config_decode(AACDecContext *ac, AVCodecContext *avctx,
> >       int map_pos_set = 0;
> >       uint8_t layout_map[MAX_ELEM_ID*4][3] = { 0 };
> > +    if (!ac)
> > +        return AVERROR_PATCHWELCOME;
> > +
> >       memset(usac, 0, sizeof(*usac));
> >       freq_idx = get_bits(gb, 5); /* usacSamplingFrequencyIndex */
> 
> This doesn't seem possible at all.
> There are 2 callers, parse_audio_preroll and
> decode_audio_specific_config_gb. Both of these will crash way before the
> function is called.
> 
> Could you at least get a backtrace?

sure

libavcodec/aac/aacdec_usac.c:402:39: runtime error: member access within null pointer of type 'AACDecContext' (aka 'struct AACDecContext')
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior libavcodec/aac/aacdec_usac.c:402:39 in
AddressSanitizer:DEADLYSIGNAL
=================================================================
==215602==ERROR: AddressSanitizer: SEGV on unknown address 0x000000005b10 (pc 0x00000154771e bp 0x7ffcf5049e90 sp 0x7ffcf5049e70 T0)
==215602==The signal is caused by a READ memory access.
    #0 0x154771d in av_channel_layout_uninit ffmpeg/libavutil/channel_layout.c:439:25
    #1 0x57346e in ff_aac_usac_config_decode ffmpeg/libavcodec/aac/aacdec_usac.c:402:9
    #2 0x500a0a in decode_audio_specific_config_gb ffmpeg/libavcodec/aac/aacdec.c:1050:20
    #3 0x50a542 in latm_decode_audio_specific_config ffmpeg/libavcodec/aac/aacdec_latm.h:80:21
    #4 0x4f8638 in read_stream_mux_config ffmpeg/libavcodec/aac/aacdec_latm.h:160:24
    #5 0x4f8638 in read_audio_mux_element ffmpeg/libavcodec/aac/aacdec_latm.h:233
    #6 0x4f8638 in latm_decode_frame ffmpeg/libavcodec/aac/aacdec_latm.h:275
    #7 0x68f26f in decode_simple_internal ffmpeg/libavcodec/decode.c:429:20
    #8 0x68f26f in decode_simple_receive_frame ffmpeg/libavcodec/decode.c:600
    #9 0x68f26f in decode_receive_frame_internal ffmpeg/libavcodec/decode.c:631
    #10 0x68dc9d in avcodec_send_packet ffmpeg/libavcodec/decode.c:721:15
    #11 0x4d1e55 in LLVMFuzzerTestOneInput ffmpeg/tools/target_dec_fuzzer.c:534:25


[...]


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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Elect your leaders based on what they did after the last election, not
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