[FFmpeg-cvslog] mxfdec: Never seek back in local sets and KLVs

[Tomas Härdin]

ffmpeg | branch: master | Tomas Härdin <tomas.hardin at codemill.se> | Wed Dec 21 10:49:27 2011 +0100| [e7839602f469eb9dd5e1341d780c0c1667ac89ad] | committer: Tomas Härdin

mxfdec: Never seek back in local sets and KLVs

Specially crafted files can lead the parsing code to take too long.
We fix a lot of these problems by not allowing local tags to extend past the
end of the set and not allowing other KLVs to be read past the end of
themselves.

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=e7839602f469eb9dd5e1341d780c0c1667ac89ad
---

 libavformat/mxfdec.c |   15 +++++++++++++++
 1 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/libavformat/mxfdec.c b/libavformat/mxfdec.c
index 5035a2f..e136374 100644
--- a/libavformat/mxfdec.c
+++ b/libavformat/mxfdec.c
@@ -1464,6 +1464,13 @@ static int mxf_read_local_tags(MXFContext *mxf, KLVPacket *klv, MXFMetadataReadF
         else if (read_child(ctx, pb, tag, size, uid, -1) < 0)
             return -1;
 
+        /* accept the 64k local set limit being exceeded (Avid)
+         * don't accept it extending past the end of the KLV though (zzuf5.mxf) */
+        if (avio_tell(pb) > klv_end) {
+            av_log(mxf->fc, AV_LOG_ERROR, "local tag %#04x extends past end of local set @ %#"PRIx64"\n",
+                   tag, klv->offset);
+            return AVERROR_INVALIDDATA;
+        } else if (avio_tell(pb) <= next)   /* only seek forward, else this can loop for a long time */
         avio_seek(pb, next, SEEK_SET);
     }
     if (ctx_size) ctx->type = type;
@@ -1667,6 +1674,14 @@ static int mxf_read_header(AVFormatContext *s, AVFormatParameters *ap)
                 } else {
                     uint64_t next = avio_tell(s->pb) + klv.length;
                     res = metadata->read(mxf, s->pb, 0, klv.length, klv.key, klv.offset);
+
+                    /* only seek forward, else this can loop for a long time */
+                    if (avio_tell(s->pb) > next) {
+                        av_log(s, AV_LOG_ERROR, "read past end of KLV @ %#"PRIx64"\n",
+                               klv.offset);
+                        return AVERROR_INVALIDDATA;
+                    }
+
                     avio_seek(s->pb, next, SEEK_SET);
                 }
                 if (res < 0) {