[FFmpeg-cvslog] avcodec/ralf: Skip initializing unused filter variables

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Sat Oct  5 19:34:17 2019 +0200| [f4ecf6c39de9a7cc1dae70cf87c225771001e883] | committer: Michael Niedermayer

avcodec/ralf: Skip initializing unused filter variables

Fixes: left shift of negative value -1
Fixes: 17890/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_RALF_fuzzer-5643307467669504

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=f4ecf6c39de9a7cc1dae70cf87c225771001e883
---

 libavcodec/ralf.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/libavcodec/ralf.c b/libavcodec/ralf.c
index 006ab46414..1d881cf7ae 100644
--- a/libavcodec/ralf.c
+++ b/libavcodec/ralf.c
@@ -234,8 +234,10 @@ static int decode_channel(RALFContext *ctx, GetBitContext *gb, int ch,
     int *dst = ctx->channel_data[ch];
 
     ctx->filter_params = get_vlc2(gb, set->filter_params.table, 9, 2);
-    ctx->filter_bits   = (ctx->filter_params - 2) >> 6;
-    ctx->filter_length = ctx->filter_params - (ctx->filter_bits << 6) - 1;
+    if (ctx->filter_params > 1) {
+        ctx->filter_bits   = (ctx->filter_params - 2) >> 6;
+        ctx->filter_length = ctx->filter_params - (ctx->filter_bits << 6) - 1;
+    }
 
     if (ctx->filter_params == FILTER_RAW) {
         for (i = 0; i < length; i++)