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avcodec/dstdec: Check for input exhaustion 

Fixes: Timeout (239sec -> 16sec)
Fixes: 17811/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_DST_fuzzer-5715508149616640

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
This commit is contained in:
Michael Niedermayer 2019-10-02 20:48:40 +02:00
parent a5d29812ec
commit f6df99dba1
1 changed files with 7 additions and 0 deletions
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7
libavcodec/dstdec.c
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@ -56,6 +56,7 @@ static const int8_t probs_code_pred_coeff[3][3] = {
typedef struct ArithCoder {
unsigned int a;
unsigned int c;
int overread;
} ArithCoder;
typedef struct Table {
@ -172,6 +173,7 @@ static void ac_init(ArithCoder *ac, GetBitContext *gb)
{
ac->a = 4095;
ac->c = get_bits(gb, 12);
ac->overread = 0;
}
static av_always_inline void ac_get(ArithCoder *ac, GetBitContext *gb, int p, int *e)
@ -191,6 +193,8 @@ static av_always_inline void ac_get(ArithCoder *ac, GetBitContext *gb, int p, in
if (ac->a < 2048) {
int n = 11 - av_log2(ac->a);
ac->a <<= n;
if (get_bits_left(gb) < n)
ac->overread ++;
ac->c = (ac->c << n) | get_bits(gb, n);
}
}
@ -339,6 +343,9 @@ static int decode_frame(AVCodecContext *avctx, void *data,
prob = 128;
}
if (ac->overread > 16)
return AVERROR_INVALIDDATA;
ac_get(ac, gb, prob, &residual);
v = ((predict >> 15) ^ residual) & 1;
dsd[((i >> 3) * channels + ch) << 2] |= v << (7 - (i & 0x7 ));