[FFmpeg-cvslog] swfdec: do better validation of tag length

[Justin Ruggles]

ffmpeg | branch: release/0.10 | Justin Ruggles <justin.ruggles at gmail.com> | Mon Dec 10 12:44:09 2012 -0500| [e786cc33312083382f4ca394e67e1cb58c786289] | committer: Luca Barbato

swfdec: do better validation of tag length

Avoids trying to read a packet with 0 or negative size.
Avoids a potential infinite loop due to seeking backwards.

Partially based on a patch by Michael Niedermayer.

(cherry picked from commit e70c5b034c4787377e82cab2d5565486baec0c2a)

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

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=e786cc33312083382f4ca394e67e1cb58c786289
---

 libavformat/swfdec.c |   22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/libavformat/swfdec.c b/libavformat/swfdec.c
index 6966176..faf74c5 100644
--- a/libavformat/swfdec.c
+++ b/libavformat/swfdec.c
@@ -91,6 +91,10 @@ static int swf_read_packet(AVFormatContext *s, AVPacket *pkt)
         tag = get_swf_tag(pb, &len);
         if (tag < 0)
             return AVERROR(EIO);
+        if (len < 0) {
+            av_log(s, AV_LOG_ERROR, "invalid tag length: %d\n", len);
+            return AVERROR_INVALIDDATA;
+        }
         if (tag == TAG_VIDEOSTREAM) {
             int ch_id = avio_rl16(pb);
             len -= 2;
@@ -150,7 +154,10 @@ static int swf_read_packet(AVFormatContext *s, AVPacket *pkt)
                 st = s->streams[i];
                 if (st->codec->codec_type == AVMEDIA_TYPE_VIDEO && st->id == ch_id) {
                     frame = avio_rl16(pb);
-                    if ((res = av_get_packet(pb, pkt, len-2)) < 0)
+                    len -= 2;
+                    if (len <= 0)
+                        goto skip;
+                    if ((res = av_get_packet(pb, pkt, len)) < 0)
                         return res;
                     pkt->pos = pos;
                     pkt->pts = frame;
@@ -164,9 +171,14 @@ static int swf_read_packet(AVFormatContext *s, AVPacket *pkt)
                 if (st->codec->codec_type == AVMEDIA_TYPE_AUDIO && st->id == -1) {
             if (st->codec->codec_id == CODEC_ID_MP3) {
                 avio_skip(pb, 4);
-                if ((res = av_get_packet(pb, pkt, len-4)) < 0)
+                len -= 4;
+                if (len <= 0)
+                    goto skip;
+                if ((res = av_get_packet(pb, pkt, len)) < 0)
                     return res;
             } else { // ADPCM, PCM
+                if (len <= 0)
+                    goto skip;
                 if ((res = av_get_packet(pb, pkt, len)) < 0)
                     return res;
             }
@@ -193,7 +205,10 @@ static int swf_read_packet(AVFormatContext *s, AVPacket *pkt)
                 st = vst;
             }
             avio_rl16(pb); /* BITMAP_ID */
-            if ((res = av_new_packet(pkt, len-2)) < 0)
+            len -= 2;
+            if (len < 4)
+                goto skip;
+            if ((res = av_new_packet(pkt, len)) < 0)
                 return res;
             avio_read(pb, pkt->data, 4);
             if (AV_RB32(pkt->data) == 0xffd8ffd9 ||
@@ -210,6 +225,7 @@ static int swf_read_packet(AVFormatContext *s, AVPacket *pkt)
             return pkt->size;
         }
     skip:
+        len = FFMAX(0, len);
         avio_skip(pb, len);
     }
 }