Allow more SRTP errors before killing call

In a carrier interop we saw the call get killed for SRTP failures
during a reinvite.  We're wondering if the SRTP errors may have been
transitory and if it may have recovered after a few more packets.

It's debatable whether we should kill calls at all for SRTP auth
failures; semantically the right thing to do when a MAC fails is to
ignore the packet completely.  So raising this limit to 100 packets
shouldn't do any harm.  With this change we still warn at 10 errors
and every 10 errors thereafter.

src/switch_rtp.c

@@ -66,7 +66,8 @@
 #define RTP_END_PORT 32768
 #define MASTER_KEY_LEN   30
 #define RTP_MAGIC_NUMBER 42
-#define MAX_SRTP_ERRS 10
+#define WARN_SRTP_ERRS 10
+#define MAX_SRTP_ERRS 100
 
 #define DTMF_SANITY (rtp_session->one_second * 30)
 
@@ -4801,13 +4802,25 @@ static switch_status_t read_rtp_packet(switch_rtp_t *rtp_session, switch_size_t
 				}
 
 				if (stat && rtp_session->recv_msg.header.pt != rtp_session->recv_te && rtp_session->recv_msg.header.pt != rtp_session->cng_pt) {
-					if (++rtp_session->srtp_errs[rtp_session->srtp_idx_rtp] >= MAX_SRTP_ERRS && stat != 10) {
-						switch_channel_t *channel = switch_core_session_get_channel(rtp_session->session);
-						switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(rtp_session->session), SWITCH_LOG_ERROR,
-										  "Error: SRTP %s unprotect failed with code %d%s %ld\n", rtp_type(rtp_session), stat,
-										  stat == err_status_replay_fail ? " (replay check failed)" : stat ==
-										  err_status_auth_fail ? " (auth check failed)" : "", (long)*bytes);
-						switch_channel_hangup(channel, SWITCH_CAUSE_SRTP_READ_ERROR);
+					int errs = ++rtp_session->srtp_errs[rtp_session->srtp_idx_rtp];
+					if (stat != 10) {
+						char *msg;
+						if (stat == err_status_replay_fail) msg="replay check failed";
+						else if (stat == err_status_auth_fail) msg="auth check failed";
+						else msg="";
+						if (errs >= WARN_SRTP_ERRS && !(errs % WARN_SRTP_ERRS)) {
+							switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(rtp_session->session), SWITCH_LOG_WARNING,
+											  "SRTP %s unprotect failed with code %d (%s) %ld bytes %d errors\n",
+											  rtp_type(rtp_session), stat, msg, (long)*bytes, errs);
+						} else if (errs >= MAX_SRTP_ERRS) {
+							switch_channel_t *channel = switch_core_session_get_channel(rtp_session->session);
+							switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(rtp_session->session), SWITCH_LOG_ERROR,
+											  "SRTP %s unprotect failed with code %d (%s) %ld bytes %d errors\n",
+											  rtp_type(rtp_session), stat, msg, (long)*bytes, errs);
+							switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(rtp_session->session), SWITCH_LOG_ERROR,
+											  "Ending call due to SRTP error\n");
+							switch_channel_hangup(channel, SWITCH_CAUSE_SRTP_READ_ERROR);
+						}
 					}
 					sbytes = 0;
 				} else {