[FFmpeg-cvslog] avcodec/alsdec: Check k from being outside what our implementation can handle

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Sun Aug 25 18:22:50 2019 +0200| [e1255789941d213a8e193469d0687946c9fa4a63] | committer: Michael Niedermayer

avcodec/alsdec: Check k from being outside what our implementation can handle

The specification does not seem to list what the maximum valid
value is

Fixes: shift exponent 32 is too large for 32-bit type 'unsigned int'
Fixes: 16268/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ALS_fuzzer-5638164544225280

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=e1255789941d213a8e193469d0687946c9fa4a63
---

 libavcodec/alsdec.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/libavcodec/alsdec.c b/libavcodec/alsdec.c
index f8d10df8c6..a53c170d18 100644
--- a/libavcodec/alsdec.c
+++ b/libavcodec/alsdec.c
@@ -833,6 +833,9 @@ static int read_var_block_data(ALSDecContext *ctx, ALSBlockData *bd)
             k    [sb] = s[sb] > b ? s[sb] - b : 0;
             delta[sb] = 5 - s[sb] + k[sb];
 
+            if (k[sb] >= 32)
+                return AVERROR_INVALIDDATA;
+
             ff_bgmc_decode(gb, sb_len, current_res,
                         delta[sb], sx[sb], &high, &low, &value, ctx->bgmc_lut, ctx->bgmc_lut_status);