From c88afa44c4823aba7b6f4a1b01fd6a4169643c57 Mon Sep 17 00:00:00 2001
From: Michael Niedermayer <michael@niedermayer.cc>
Date: Sat, 15 Sep 2018 00:20:38 +0200
Subject: [PATCH] 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>
---
libavcodec/mpeg4videodec.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libavcodec/mpeg4videodec.c b/libavcodec/mpeg4videodec.c
index 853c6d91320..f435a520c8b 100644
--- a/libavcodec/mpeg4videodec.c
+++ b/libavcodec/mpeg4videodec.c
@@ -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);
--
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