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avcodec/mpeg4videodec: Fix undefined shift in get_amv() 

Fixes: runtime error: shift exponent -1 is negative
Fixes: 9938/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MPEG4_fuzzer-5653783529914368

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
This commit is contained in:
Michael Niedermayer 2018-09-15 00:20:38 +02:00
parent fb7b0347b3
commit c88afa44c4
1 changed files with 1 additions and 1 deletions
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2
libavcodec/mpeg4videodec.c
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@ -598,7 +598,7 @@ static inline int get_amv(Mpeg4DecContext *ctx, int n)
len >>= s->quarter_sample;
if (s->real_sprite_warping_points == 1) {
if (ctx->divx_version == 500 && ctx->divx_build == 413)
if (ctx->divx_version == 500 && ctx->divx_build == 413 && a >= s->quarter_sample)
sum = s->sprite_offset[0][n] / (1 << (a - s->quarter_sample));
else
sum = RSHIFT(s->sprite_offset[0][n] * (1 << s->quarter_sample), a);