res_rtp_asterisk.c: Fix bridge_p2p_rtp_write() reentrancy potential.

The bridge_p2p_rtp_write() has potential reentrancy problems.

* Accessing the bridged RTP members must be done with the instance1 lock
held.  The DTMF and asymmetric codec checks must be split to be done with
the correct RTP instance struct locked.  i.e., They must be done when
working on the appropriate side of the point to point bridge.

* Forcing the RTP mark bit was referencing the wrong side of the point to
point bridge.  The set mark bit is used everywhere else to set the mark
bit when sending not receiving.

The patches for ASTERISK_26745 and ASTERISK_27158 did not take into
account that not everything carried by RTP uses a codec.  The telephony
DTMF events are not exchanged with a codec.  As a result when
RFC2833/RFC4733 sent digits you would crash if "core set debug 1" is
enabled, the DTMF digits would always get passed to the core even though
the local native RTP bridge is active, and the DTMF digits would go out
using the wrong SSRC id.

* Add protection for non-format payload types like DTMF when updating the
lastrxformat and lasttxformat.  Also protect against non-format payload
types when checking for asymmetric codecs.

ASTERISK-27292

Change-Id: I6344ab7de21e26f84503c4d1fca1a41579364186

res/res_rtp_asterisk.c

@@ -5063,7 +5063,7 @@ static int bridge_p2p_rtp_write(struct ast_rtp_instance *instance,
 	struct ast_rtp_instance *instance1, unsigned int *rtpheader, int len, int hdrlen)
 {
 	struct ast_rtp *rtp = ast_rtp_instance_get_data(instance);
-	struct ast_rtp *bridged = ast_rtp_instance_get_data(instance1);
+	struct ast_rtp *bridged;
 	int res = 0, payload = 0, bridged_payload = 0, mark;
 	RAII_VAR(struct ast_rtp_payload_type *, payload_type, NULL, ao2_cleanup);
 	int reconstruct = ntohl(rtpheader[0]);
@@ -5073,7 +5073,7 @@ static int bridge_p2p_rtp_write(struct ast_rtp_instance *instance,
 
 	/* Get fields from packet */
 	payload = (reconstruct & 0x7f0000) >> 16;
-	mark = (((reconstruct & 0x800000) >> 23) != 0);
+	mark = (reconstruct & 0x800000) >> 23;
 
 	/* Check what the payload value should be */
 	payload_type = ast_rtp_codecs_get_payload(ast_rtp_instance_get_codecs(instance), payload);
@@ -5095,12 +5095,6 @@ static int bridge_p2p_rtp_write(struct ast_rtp_instance *instance,
 		return -1;
 	}
 
-	/* If bridged peer is in dtmf, feed all packets to core until it finishes to avoid infinite dtmf */
-	if (bridged->sending_digit) {
-		ast_debug(1, "Feeding packets to core until DTMF finishes\n");
-		return -1;
-	}
-
 	/*
 	 * Even if we are no longer in dtmf, we could still be receiving
 	 * re-transmissions of the last dtmf end still.  Feed those to the
@@ -5111,35 +5105,10 @@ static int bridge_p2p_rtp_write(struct ast_rtp_instance *instance,
 		return -1;
 	}
 
-
+	if (payload_type->asterisk_format) {
-	ao2_replace(rtp->lastrxformat, payload_type->format);
+		ao2_replace(rtp->lastrxformat, payload_type->format);
-	ao2_replace(bridged->lasttxformat, payload_type->format);
-
-	/*
-	 * If bridged peer has already received rtp, perform the asymmetric codec check
-	 * if that feature has been activated
-	 */
-	if (!bridged->asymmetric_codec && bridged->lastrxformat != ast_format_none) {
-		if (ast_format_cmp(bridged->lasttxformat, bridged->lastrxformat) == AST_FORMAT_CMP_NOT_EQUAL) {
-			ast_debug(1, "Asymmetric RTP codecs detected (TX: %s, RX: %s) sending frame to core\n",
-					ast_format_get_name(bridged->lasttxformat),
-					ast_format_get_name(bridged->lastrxformat));
-			return -1;
-		}
 	}
 
-	/* If the marker bit has been explicitly set turn it on */
-	if (ast_test_flag(rtp, FLAG_NEED_MARKER_BIT)) {
-		mark = 1;
-		ast_clear_flag(rtp, FLAG_NEED_MARKER_BIT);
-	}
-
-	/* Reconstruct part of the packet */
-	reconstruct &= 0xFF80FFFF;
-	reconstruct |= (bridged_payload << 16);
-	reconstruct |= (mark << 23);
-	rtpheader[0] = htonl(reconstruct);
-
 	/*
 	 * We have now determined that we need to send the RTP packet
 	 * out the bridged instance to do local bridging so we must unlock
@@ -5155,6 +5124,40 @@ static int bridge_p2p_rtp_write(struct ast_rtp_instance *instance,
 	ao2_unlock(instance);
 	ao2_lock(instance1);
 
+	/*
+	 * Get the peer rtp pointer now to emphasize that using it
+	 * must happen while instance1 is locked.
+	 */
+	bridged = ast_rtp_instance_get_data(instance1);
+
+
+	/* If bridged peer is in dtmf, feed all packets to core until it finishes to avoid infinite dtmf */
+	if (bridged->sending_digit) {
+		ast_debug(1, "Feeding packet to core until DTMF finishes\n");
+		ao2_unlock(instance1);
+		ao2_lock(instance);
+		return -1;
+	}
+
+	if (payload_type->asterisk_format) {
+		/*
+		 * If bridged peer has already received rtp, perform the asymmetric codec check
+		 * if that feature has been activated
+		 */
+		if (!bridged->asymmetric_codec
+			&& bridged->lastrxformat != ast_format_none
+			&& ast_format_cmp(payload_type->format, bridged->lastrxformat) == AST_FORMAT_CMP_NOT_EQUAL) {
+			ast_debug(1, "Asymmetric RTP codecs detected (TX: %s, RX: %s) sending frame to core\n",
+				ast_format_get_name(payload_type->format),
+				ast_format_get_name(bridged->lastrxformat));
+			ao2_unlock(instance1);
+			ao2_lock(instance);
+			return -1;
+		}
+
+		ao2_replace(bridged->lasttxformat, payload_type->format);
+	}
+
 	ast_rtp_instance_get_remote_address(instance1, &remote_address);
 
 	if (ast_sockaddr_isnull(&remote_address)) {
@@ -5164,6 +5167,18 @@ static int bridge_p2p_rtp_write(struct ast_rtp_instance *instance,
 		return 0;
 	}
 
+	/* If the marker bit has been explicitly set turn it on */
+	if (ast_test_flag(bridged, FLAG_NEED_MARKER_BIT)) {
+		mark = 1;
+		ast_clear_flag(bridged, FLAG_NEED_MARKER_BIT);
+	}
+
+	/* Reconstruct part of the packet */
+	reconstruct &= 0xFF80FFFF;
+	reconstruct |= (bridged_payload << 16);
+	reconstruct |= (mark << 23);
+	rtpheader[0] = htonl(reconstruct);
+
 	/* Send the packet back out */
 	res = rtp_sendto(instance1, (void *)rtpheader, len, 0, &remote_address, &ice);
 	if (res < 0) {