[FFmpeg-cvslog] nutdec: reject negative value_len in read_sm_data

[Andreas Cadhalpun]

ffmpeg | branch: release/2.6 | Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com> | Sat Dec 19 12:02:56 2015 +0100| [4d2f9368034353037ae4fb96c1156848fe0ebe7a] | committer: Andreas Cadhalpun

nutdec: reject negative value_len in read_sm_data

If it is negative, it can cause the byte position to move backwards in
avio_skip, which in turn makes sm_size negative and thus size larger
than the size of the packet buffer, causing invalid writes in avio_read.

Also fix potential overflow of avio_tell(bc) + value_len.

Reviewed-by: Michael Niedermayer <michael at niedermayer.cc>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>
(cherry picked from commit ce10f572c12b0d172c72d31d8c979afce602bf0c)
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=4d2f9368034353037ae4fb96c1156848fe0ebe7a
---

 libavformat/nutdec.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavformat/nutdec.c b/libavformat/nutdec.c
index cdcce64..e0f106a 100644
--- a/libavformat/nutdec.c
+++ b/libavformat/nutdec.c
@@ -872,7 +872,7 @@ static int read_sm_data(AVFormatContext *s, AVIOContext *bc, AVPacket *pkt, int
 
             get_str(bc, type_str, sizeof(type_str));
             value_len = ffio_read_varlen(bc);
-            if (avio_tell(bc) + value_len >= maxpos)
+            if (value_len < 0 || value_len >= maxpos - avio_tell(bc))
                 return AVERROR_INVALIDDATA;
             if (!strcmp(name, "Palette")) {
                 dst = av_packet_new_side_data(pkt, AV_PKT_DATA_PALETTE, value_len);