From: George Joseph <gjoseph@digium.com>
Date: Wed, 18 May 2016 12:54:14 +0000 (-0600)
Subject: udptl: Don't eat sequence numbers until OK is received
X-Git-Tag: certified/11.6-cert14-rc1~16^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1597ef14ed4bee3bef044ccb9f78673fec210474;p=thirdparty%2Fasterisk.git

udptl: Don't eat sequence numbers until OK is received

Scenario:
Local fax -> Asterisk w/ firewall -> Provider -> Remote fax

* Local fax starts rtp call to remote fax
* Remote fax starts t38 call back to local fax.
* Local fax sends t38 no-signal to Asterisk before sending an OK.
* udptl processes the frame and increments the expected sequence number.
* chan_sip drops the frame because the call isn't up so nothing goes out
  the external interface to open the port for incoming packets.
* Local fax sends OK and Asterisk sends OK to the remote fax.
* Remote fax sends t38 packets which are dropped by the firewall.
* Local fax re-sends t38 no-signal with the same sequence number.
* udptl drops the frame because it thinks it's a dup.
* Still no outgoing packets to open the firewall.
* t38 negotiation fails.

The patch drops frames t38 received before udptl sequence processing
when the call hasn't been answered yet.  The second no-signal frame
is then seen as new and is relayed out the external interface which
opens the port and allows negotiation to continue.

ASTERISK-26034 #close

Change-Id: I11744b39748bd2ecbbe8ea84cdb4f3c5943c5af9
---

diff --git a/main/udptl.c b/main/udptl.c
index b582008a53..9e14bc45b7 100644
--- a/main/udptl.c
+++ b/main/udptl.c
@@ -724,6 +724,18 @@ struct ast_frame *ast_udptl_read(struct ast_udptl *udptl)
 		return &ast_null_frame;
 	}
 
+	/*
+	 * If early media isn't turned on for the channel driver, it's going to
+	 * drop this frame.  By that time though, udptl has already incremented
+	 * the expected sequence number so if the CPE re-sends, the second frame
+	 * will be dropped as a dup even though the first frame never went through.
+	 * So we drop the frame here if the channel isn't up. 'tag' is set by the
+	 * channel drivers on T38_ENABLED or T38_PEER_REINVITE.
+	 */
+	if (udptl->tag == NULL) {
+		return &ast_null_frame;
+	}
+
 	if (udptl->nat) {
 		/* Send to whoever sent to us */
 		if (ast_sockaddr_cmp(&udptl->them, &addr)) {