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

[Lynne via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

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On 26/06/2024 21:45, Andreas Rheinhardt wrote:
> Lynne via ffmpeg-devel:
>> On 26/06/2024 01:57, Michael Niedermayer wrote:
>>> 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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>>
>> This patch actually is correct.
>> USAC in LATM is not supported AFAIK.
>>
>> LGTM with a note like:
>> "Happens only when the LATM decoder is used, and USAC is not supported
>> in LATM".
>>
> 
> But then it is not PATCHWELCOME, but INVALIDDATA.

I got an email from one of the developers who informed me that its 
supported in LATM.
But, I have no samples, so patch welcome is fine for now.

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