implement detection of duplicate packets to catch and avoid forwarding loops

fixes #20

daemon/call.c

@@ -575,6 +575,7 @@ static int stream_packet(struct stream_fd *sfd, str *s, struct sockaddr_in6 *fsi
 	struct call_media *media;
 	int ret = 0, update = 0, stun_ret = 0, handler_ret = 0, muxed_rtcp = 0, rtcp = 0,
 	    unk = 0;
+	int i;
 	struct sockaddr_in6 sin6;
 	struct msghdr mh;
 	struct iovec iov;
@@ -621,6 +622,32 @@ static int stream_packet(struct stream_fd *sfd, str *s, struct sockaddr_in6 *fsi
 			stun_ret = 0;
 	}
 
+#if RTP_LOOP_PROTECT
+	for (i = 0; i < RTP_LOOP_PACKETS; i++) {
+		if (stream->lp_buf[i].len != s->len)
+			continue;
+		if (memcmp(stream->lp_buf[i].buf, s->s, MIN(s->len, RTP_LOOP_PROTECT)))
+			continue;
+
+		__C_DBG("packet dupe");
+		if (stream->lp_count >= RTP_LOOP_MAX_COUNT) {
+			ilog(LOG_WARNING, "More than %d duplicate packets detected, dropping packet "
+					"to avoid potential loop", RTP_LOOP_MAX_COUNT);
+			goto done;
+		}
+
+		stream->lp_count++;
+		goto loop_ok;
+	}
+
+	/* not a dupe */
+	stream->lp_count = 0;
+	stream->lp_buf[stream->lp_idx].len = s->len;
+	memcpy(stream->lp_buf[stream->lp_idx].buf, s->s, MIN(s->len, RTP_LOOP_PROTECT));
+	stream->lp_idx = (stream->lp_idx + 1) % RTP_LOOP_PACKETS;
+loop_ok:
+#endif
+
 	mutex_unlock(&stream->in_lock);
 
 	in_srtp = stream;

daemon/call.h

@@ -65,6 +65,12 @@ struct call_monologue;
 #define RTP_BUFFER_TAIL_ROOM	512
 #define RTP_BUFFER_SIZE		(MAX_RTP_PACKET_SIZE + RTP_BUFFER_HEAD_ROOM + RTP_BUFFER_TAIL_ROOM)
 
+#ifndef RTP_LOOP_PROTECT
+#define RTP_LOOP_PROTECT	16 /* number of bytes */
+#define RTP_LOOP_PACKETS	2  /* number of packets */
+#define RTP_LOOP_MAX_COUNT	30 /* number of consecutively detected dupes to trigger protection */
+#endif
+
 #ifdef __DEBUG
 #define __C_DBG(x...) ilog(LOG_DEBUG, x)
 #else
@@ -215,6 +221,11 @@ struct endpoint_map {
 	int			wildcard:1;
 };
 
+struct loop_protector {
+	unsigned int		len;
+	unsigned char		buf[RTP_LOOP_PROTECT];
+};
+
 struct packet_stream {
 	mutex_t			in_lock,
 				out_lock;
@@ -238,6 +249,13 @@ struct packet_stream {
 	struct stats		kernel_stats;	/* LOCK: in_lock */
 	time_t			last_packet;	/* LOCK: in_lock */
 
+#if RTP_LOOP_PROTECT
+	/* LOCK: in_lock: */
+	unsigned int		lp_idx;
+	struct loop_protector	lp_buf[RTP_LOOP_PACKETS];
+	unsigned int		lp_count;
+#endif
+
 	X509			*dtls_cert;	/* LOCK: in_lock */
 
 	/* in_lock must be held for SETTING these: */