chan_sip: Allow Preferred sRTP.
authorAlexander Traud <pabstraud@compuserve.com>
Tue, 19 Jul 2016 14:41:44 +0000 (16:41 +0200)
committerJoshua Colp <jcolp@digium.com>
Wed, 7 Sep 2016 11:45:23 +0000 (11:45 +0000)
Following the Encrypt-all-the-things paradigm:

The user enters his SIP-URI and password. Thanks to DNS-NAPTR, the phone
determines SIP-over-TLS as preferred transport. In SIP/SDP, the phone starts
the call with a crypto attribute, but not as RTP/sAVP but the RTP/AVP profile
(sRTP is preferred aka optional; not mandatory). If the VoIP server does not
support sRTP and TLS, the phone shows an open padlock icon.

This paradigm is supported by several VoIP/SIP clients on default. Some
implementations even cannot be changed to RTP/sAVP. Therefore here, this
change allows Preferred sRTP for ingress. For egress, please, create a dial
plan which starts with RTP/SAVP, and when rejected tries again with RTP/AVP.

ASTERISK-20234 #close
Reported by: tootai
Tested by: tootai, Alexander Traud
patches:
 srtp_patches.diff submitted by Matt Jordan

Change-Id: I42cb779df3a9c7b3dd03a629fb3a296aa4ceb0fd

CHANGES
channels/chan_sip.c

diff --git a/CHANGES b/CHANGES
index 5857165..8a6c673 100644 (file)
--- a/CHANGES
+++ b/CHANGES
 --- Functionality changes from Asterisk 14 to Asterisk 15 --------------------
 ------------------------------------------------------------------------------
 
+chan_sip
+------------------
+ * If an offer is received with optional SRTP (a media stream with RTP/AVP but
+   which contains a crypto line) chan_sip will now accept it and enable SRTP.
+   If you would like to do optional SRTP on outbound you will need to create
+   a dialplan that dials with it enabled initially and if it fails fall back to
+   without.
 
 ------------------------------------------------------------------------------
 --- Functionality changes from Asterisk 14.0.0 to Asterisk 14.1.0 ----------
index 6a18aa3..1d70e89 100644 (file)
@@ -1480,7 +1480,7 @@ static void handle_response(struct sip_pvt *p, int resp, const char *rest, struc
 
 /*------ SRTP Support -------- */
 static int process_crypto(struct sip_pvt *p, struct ast_rtp_instance *rtp, struct ast_sdp_srtp **srtp,
-               const char *a, int secure_transport);
+               const char *a);
 
 /*------ T38 Support --------- */
 static int transmit_response_with_t38_sdp(struct sip_pvt *p, char *msg, struct sip_request *req, int retrans);
@@ -10610,9 +10610,13 @@ static int process_sdp(struct sip_pvt *p, struct sip_request *req, int t38action
                                                }
                                        } else if (process_sdp_a_sendonly(value, &sendonly)) {
                                                processed = TRUE;
-                                       } else if (!processed_crypto && process_crypto(p, p->rtp, &p->srtp, value, secure_audio)) {
+                                       } else if (!processed_crypto && process_crypto(p, p->rtp, &p->srtp, value)) {
                                                processed_crypto = TRUE;
                                                processed = TRUE;
+                                               if (secure_audio == FALSE) {
+                                                       ast_log(AST_LOG_NOTICE, "Processed audio crypto attribute without SAVP specified; accepting anyway\n");
+                                                       secure_audio = TRUE;
+                                               }
                                        } else if (process_sdp_a_audio(value, p, &newaudiortp, &last_rtpmap_codec)) {
                                                processed = TRUE;
                                        }
@@ -10627,9 +10631,13 @@ static int process_sdp(struct sip_pvt *p, struct sip_request *req, int t38action
                                                if (p->vsrtp) {
                                                        ast_set_flag(p->vsrtp, AST_SRTP_CRYPTO_OFFER_OK);
                                                }
-                                       } else if (!processed_crypto && process_crypto(p, p->vrtp, &p->vsrtp, value, secure_video)) {
+                                       } else if (!processed_crypto && process_crypto(p, p->vrtp, &p->vsrtp, value)) {
                                                processed_crypto = TRUE;
                                                processed = TRUE;
+                                               if (secure_video == FALSE) {
+                                                       ast_log(AST_LOG_NOTICE, "Processed video crypto attribute without SAVP specified; accepting anyway\n");
+                                                       secure_video = TRUE;
+                                               }
                                        } else if (process_sdp_a_video(value, p, &newvideortp, &last_rtpmap_codec)) {
                                                processed = TRUE;
                                        }
@@ -10640,7 +10648,7 @@ static int process_sdp(struct sip_pvt *p, struct sip_request *req, int t38action
                                                processed = TRUE;
                                        } else if (process_sdp_a_text(value, p, &newtextrtp, red_fmtp, &red_num_gen, red_data_pt, &last_rtpmap_codec)) {
                                                processed = TRUE;
-                                       } else if (!processed_crypto && process_crypto(p, p->trtp, &p->tsrtp, value, 1)) {
+                                       } else if (!processed_crypto && process_crypto(p, p->trtp, &p->tsrtp, value)) {
                                                processed_crypto = TRUE;
                                                processed = TRUE;
                                        }
@@ -33752,7 +33760,7 @@ static void sip_send_all_mwi_subscriptions(void)
 }
 
 static int process_crypto(struct sip_pvt *p, struct ast_rtp_instance *rtp, struct ast_sdp_srtp **srtp,
-               const char *a, int secure_transport)
+               const char *a)
 {
        struct ast_rtp_engine_dtls *dtls;
 
@@ -33768,23 +33776,6 @@ static int process_crypto(struct sip_pvt *p, struct ast_rtp_instance *rtp, struc
        /* skip "crypto:" */
        a += strlen("crypto:");
 
-       if (!secure_transport) {
-               /* > The Secure Real-time Transport Protocol (SRTP)
-                * > [RFC3711] provides security services for RTP media
-                * > and is signaled by use of secure RTP transport (e.g.,
-                * > "RTP/SAVP" or "RTP/SAVPF") in an SDP media (m=) line.
-                * > ...
-                * > The "crypto" attribute MUST only appear at the SDP
-                * > media level (not at the session level).
-                *
-                * Ergo, we can trust RTP/(S)AVP to be read from the m=
-                * line before we get here. If it was RTP/AVP, then this
-                * is SNOM-specific optional SRTP. Ignore it.
-                */
-               ast_log(LOG_WARNING, "Ignoring crypto attribute in SDP because RTP transport is insecure\n");
-               return FALSE;
-       }
-
        if (!*srtp) {
                if (ast_test_flag(&p->flags[0], SIP_OUTGOING)) {
                        ast_log(LOG_WARNING, "Ignoring unexpected crypto attribute in SDP answer\n");