[FFmpeg-cvslog] rtmppkt: Check for packet size mismatches

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Mon Dec  5 11:14:51 2016 +0100| [a4fec9a7eab842ea5eea1b1ee98624356cb31422] | committer: Martin Storsjö

rtmppkt: Check for packet size mismatches

When receiving fragmented packets, the first packet declares the size,
and the later ones normally are small follow-on packets that don't repeat
the size and the other header fields. But technically, the later fragments
also can have a full header, declaring a different size than the previous
packet.

If the follow-on packet declares a larger size than the initial one, we
could end up writing outside of the allocation.

This fixes out of bounds writes.

Found-by: Paul Cher <paulcher at icloud.com>
Reviewed-by: Paul Cher <paulcher at icloud.com>

CC: libav-stable at libav.org
Signed-off-by: Martin Storsjö <martin at martin.st>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=a4fec9a7eab842ea5eea1b1ee98624356cb31422
---

 libavformat/rtmppkt.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/libavformat/rtmppkt.c b/libavformat/rtmppkt.c
index f8c51d01fa..1cb3078679 100644
--- a/libavformat/rtmppkt.c
+++ b/libavformat/rtmppkt.c
@@ -235,6 +235,14 @@ static int rtmp_packet_read_one_chunk(URLContext *h, RTMPPacket *p,
     if (hdr != RTMP_PS_TWELVEBYTES)
         timestamp += prev_pkt[channel_id].timestamp;
 
+    if (prev_pkt[channel_id].read && size != prev_pkt[channel_id].size) {
+        av_log(h, AV_LOG_ERROR, "RTMP packet size mismatch %d != %d\n",
+                                size, prev_pkt[channel_id].size);
+        ff_rtmp_packet_destroy(&prev_pkt[channel_id]);
+        prev_pkt[channel_id].read = 0;
+        return AVERROR_INVALIDDATA;
+    }
+
     if (!prev_pkt[channel_id].read) {
         if ((ret = ff_rtmp_packet_create(p, channel_id, type, timestamp,
                                          size)) < 0)