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avcodec/alac: Check decorr_shift to avoid invalid shift 

Later the decorrelate_stereo call is guarded by channels == 2
and non-zero decorr_left_weight. Make sure decorr_shift is in
the expected shift range for that case.

Fixes: shift exponent 128 is too large for 32-bit type 'int'
Fixes: 23860/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ALAC_fuzzer-5751138914402304

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Alexander Strasser <eclipse7@gmx.net>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
This commit is contained in:
Michael Niedermayer 2020-07-23 23:41:27 +02:00
parent 21442a820a
commit 4333718b35
1 changed files with 3 additions and 0 deletions
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libavcodec/alac.c
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@ -302,6 +302,9 @@ static int decode_element(AVCodecContext *avctx, AVFrame *frame, int ch_index,
decorr_shift = get_bits(&alac->gb, 8);
decorr_left_weight = get_bits(&alac->gb, 8);
if (channels == 2 && decorr_left_weight && decorr_shift > 31)
return AVERROR_INVALIDDATA;
for (ch = 0; ch < channels; ch++) {
prediction_type[ch] = get_bits(&alac->gb, 4);
lpc_quant[ch] = get_bits(&alac->gb, 4);