[FFmpeg-cvslog] mdec: check for out of bounds read

[Federico Tomassetti]

ffmpeg | branch: release/2.2 | Federico Tomassetti <ftomassetti at groupon.com> | Wed Feb 18 12:11:43 2015 +0000| [b2b359f12465c8445484be24278b324da8ebb0e1] | committer: Vittorio Giovara

mdec: check for out of bounds read

Bug-Id: CID 1257501
CC: libav-stable at libav.org

Signed-off-by: Luca Barbato <lu_zero at gentoo.org>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=b2b359f12465c8445484be24278b324da8ebb0e1
---

 libavcodec/mdec.c |   20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/libavcodec/mdec.c b/libavcodec/mdec.c
index b9ffca6..b0d8518 100644
--- a/libavcodec/mdec.c
+++ b/libavcodec/mdec.c
@@ -83,7 +83,12 @@ static inline int mdec_decode_block_intra(MDECContext *a, int16_t *block, int n)
             if (level == 127) {
                 break;
             } else if (level != 0) {
-                i    += run;
+                i += run;
+                if (i > 63) {
+                    av_log(a->avctx, AV_LOG_ERROR,
+                           "ac-tex damaged at %d %d\n", a->mb_x, a->mb_y);
+                    return AVERROR_INVALIDDATA;
+                }
                 j     = scantable[i];
                 level = (level * qscale * quant_matrix[j]) >> 3;
                 level = (level ^ SHOW_SBITS(re, &a->gb, 1)) - SHOW_SBITS(re, &a->gb, 1);
@@ -93,8 +98,13 @@ static inline int mdec_decode_block_intra(MDECContext *a, int16_t *block, int n)
                 run = SHOW_UBITS(re, &a->gb, 6)+1; LAST_SKIP_BITS(re, &a->gb, 6);
                 UPDATE_CACHE(re, &a->gb);
                 level = SHOW_SBITS(re, &a->gb, 10); SKIP_BITS(re, &a->gb, 10);
-                i    += run;
-                j     = scantable[i];
+                i += run;
+                if (i > 63) {
+                    av_log(a->avctx, AV_LOG_ERROR,
+                           "ac-tex damaged at %d %d\n", a->mb_x, a->mb_y);
+                    return AVERROR_INVALIDDATA;
+                }
+                j = scantable[i];
                 if (level < 0) {
                     level = -level;
                     level = (level * qscale * quant_matrix[j]) >> 3;
@@ -105,10 +115,6 @@ static inline int mdec_decode_block_intra(MDECContext *a, int16_t *block, int n)
                     level = (level - 1) | 1;
                 }
             }
-            if (i > 63) {
-                av_log(a->avctx, AV_LOG_ERROR, "ac-tex damaged at %d %d\n", a->mb_x, a->mb_y);
-                return AVERROR_INVALIDDATA;
-            }
 
             block[j] = level;
         }