avcodec/interplayacm: Fix overflow of last unused value

Fixes: signed integer overflow: -2147450880 - 65535 cannot be represented in type 'int'
Fixes: 18393/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_INTERPLAY_ACM_fuzzer-5667520110919680
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

diff --git a/libavcodec/interplayacm.c b/libavcodec/interplayacm.c
index cff79eb6b2221861e3c92beafbef0f65df6cd6e7..3704d1a2f2df4fc749e81327f3bd80df081079c3 100644 (file)
--- a/libavcodec/interplayacm.c
+++ b/libavcodec/interplayacm.c
@@ -529,7 +529,7 @@ static int decode_block(InterplayACMContext *s)
 
     for (i = 1, x = -val; i <= count; i++) {
         s->midbuf[-i] = x;
-        x -= val;
+        x -= (unsigned)val;
     }
 
     ret = fill_block(s);