[FFmpeg-devel] [PATCH] mss2: Fix buffer overflow.

Reimar Döffinger Reimar.Doeffinger at gmx.de
Thu Feb 25 21:06:46 CET 2016


Reported as https://trac.mplayerhq.hu/ticket/2264 but have
not been able to reproduce with FFmpeg-only.
I have no idea what coded_height is used for here exactly,
so this might not be the best fix.
Fixes the following chain of events:
ff_mss12_decode_init sets coded_height while not setting height.
ff_mpv_decode_init then copies coded_height into MpegEncContext height.
This is then used by init_context_frame to allocate the data structures.
However the wmv9rects are validated/initialized based on avctx->height, not
avctx->coded_height.
Thus the decode_wmv9 function will try to decode a larger video that we
allocated data structures for, causing out-of-bounds writes.

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger at gmx.de>
---
 libavcodec/mss12.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libavcodec/mss12.c b/libavcodec/mss12.c
index 6b58aa29..d42093b 100644
--- a/libavcodec/mss12.c
+++ b/libavcodec/mss12.c
@@ -581,8 +581,8 @@ av_cold int ff_mss12_decode_init(MSS12Context *c, int version,
         return AVERROR_INVALIDDATA;
     }
 
-    avctx->coded_width  = AV_RB32(avctx->extradata + 20);
-    avctx->coded_height = AV_RB32(avctx->extradata + 24);
+    avctx->coded_width  = FFMAX(AV_RB32(avctx->extradata + 20), avctx->width);
+    avctx->coded_height = FFMAX(AV_RB32(avctx->extradata + 24), avctx->height);
     if (avctx->coded_width > 4096 || avctx->coded_height > 4096) {
         av_log(avctx, AV_LOG_ERROR, "Frame dimensions %dx%d too large",
                avctx->coded_width, avctx->coded_height);
-- 
2.7.0



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