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

From: Lynne via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>
To: ffmpeg-devel@ffmpeg.org
Cc: Lynne <dev@lynne.ee>
Subject: Re: [FFmpeg-devel] [PATCH 1/5] avcodec/aac/aacdec_usac: Test ac in usac
Date: Wed, 26 Jun 2024 01:35:18 +0200
Message-ID: <2e1d95e9-b179-412c-ad81-f30bd32fef2a@lynne.ee> (raw)
In-Reply-To: <20240623230137.1749178-1-michael@niedermayer.cc>

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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?

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