[FFmpeg-cvslog] wmalosslessdec: fix a get_bits(0) in decode_ac_filter

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michaelni at gmx.at> | Sat Apr 14 14:50:25 2012 +0200| [f48fbf2eb5ba7015c65b31c266edf399dd6a82b1] | committer: Anton Khirnov

wmalosslessdec: fix a get_bits(0) in decode_ac_filter

Fixes a part of CVE-2012-2795

CC:libav-stable at libav.org

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Anton Khirnov <anton at khirnov.net>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=f48fbf2eb5ba7015c65b31c266edf399dd6a82b1
---

 libavcodec/wmalosslessdec.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/libavcodec/wmalosslessdec.c b/libavcodec/wmalosslessdec.c
index cfa877f..dc83b06 100644
--- a/libavcodec/wmalosslessdec.c
+++ b/libavcodec/wmalosslessdec.c
@@ -406,7 +406,8 @@ static void decode_ac_filter(WmallDecodeCtx *s)
     s->acfilter_scaling = get_bits(&s->gb, 4);
 
     for (i = 0; i < s->acfilter_order; i++)
-        s->acfilter_coeffs[i] = get_bits(&s->gb, s->acfilter_scaling) + 1;
+        s->acfilter_coeffs[i] = (s->acfilter_scaling ?
+                                 get_bits(&s->gb, s->acfilter_scaling) : 0) + 1;
 }
 
 static void decode_mclms(WmallDecodeCtx *s)