[FFmpeg-cvslog] dv: Fix small stack overread related to CVE-2011-3929 and CVE-2011-3936.

[Alex Converse]

ffmpeg | branch: release/0.6 | Alex Converse <alex.converse at gmail.com> | Thu Jan 26 15:08:26 2012 -0800| [a8f4db0acd9b588ba33e3b8c0c21feea5916cfd1] | committer: Reinhard Tartler

dv: Fix small stack overread related to CVE-2011-3929 and CVE-2011-3936.

Found with asan.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Alex Converse <alex.converse at gmail.com>
(cherry picked from commit 2d1c0dea5f6b91bec7f5fa53ec050913d851e366)
Signed-off-by: Reinhard Tartler <siretart at tauware.de>
(cherry picked from commit 00fa6ffe1a0b252d6a81815e51f125225cd0b97a)

Signed-off-by: Reinhard Tartler <siretart at tauware.de>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=a8f4db0acd9b588ba33e3b8c0c21feea5916cfd1
---

 libavformat/dv.c |   11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/libavformat/dv.c b/libavformat/dv.c
index 92b93f7..d65d4ff 100644
--- a/libavformat/dv.c
+++ b/libavformat/dv.c
@@ -125,10 +125,14 @@ static int dv_extract_audio(uint8_t* frame, uint8_t* ppcm[4],
     /* We work with 720p frames split in half, thus even frames have
      * channels 0,1 and odd 2,3. */
     ipcm = (sys->height == 720 && !(frame[1] & 0x0C)) ? 2 : 0;
-    pcm  = ppcm[ipcm++];
 
     /* for each DIF channel */
     for (chan = 0; chan < sys->n_difchan; chan++) {
+        /* next stereo channel (50Mbps and 100Mbps only) */
+        pcm = ppcm[ipcm++];
+        if (!pcm)
+            break;
+
         /* for each DIF segment */
         for (i = 0; i < sys->difseg_size; i++) {
             frame += 6 * 80; /* skip DIF segment header */
@@ -176,11 +180,6 @@ static int dv_extract_audio(uint8_t* frame, uint8_t* ppcm[4],
                 frame += 16 * 80; /* 15 Video DIFs + 1 Audio DIF */
             }
         }
-
-        /* next stereo channel (50Mbps and 100Mbps only) */
-        pcm = ppcm[ipcm++];
-        if (!pcm)
-            break;
     }
 
     return size;