[FFmpeg-cvslog] avcodec/ffv1dec: Check k in get_vlc_symbol()

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Wed Jul 16 00:01:07 2025 +0200| [051e0d7744dbb45f680bbfa72bfead947b11ef2f] | committer: Michael Niedermayer

avcodec/ffv1dec: Check k in get_vlc_symbol()

The true problem happens in several previous get_vlc_symbol()
but checking that is more expensive (involving FFABS())
here its just a simple check between 2 variables we have.

Fixes: Assertion log >= k failed at libavcodec/golomb.h:406
Fixes: 429296194/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FFV1_DEC_fuzzer-4691594622337024

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=051e0d7744dbb45f680bbfa72bfead947b11ef2f
---

 libavcodec/ffv1dec.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/libavcodec/ffv1dec.c b/libavcodec/ffv1dec.c
index d613aa5395..d709e8ccbb 100644
--- a/libavcodec/ffv1dec.c
+++ b/libavcodec/ffv1dec.c
@@ -56,6 +56,11 @@ static inline int get_vlc_symbol(GetBitContext *gb, VlcState *const state,
         k++;
         i += i;
     }
+    if (k > bits) {
+        ff_dlog(NULL, "k-overflow bias:%d error:%d drift:%d count:%d k:%d",
+                state->bias, state->error_sum, state->drift, state->count, k);
+        k = bits;
+    }
 
     v = get_sr_golomb(gb, k, 12, bits);
     ff_dlog(NULL, "v:%d bias:%d error:%d drift:%d count:%d k:%d",