Allow for reloading SRTP crypto keys within the same SIP dialog

As a continuation of the patch in r356604, which allowed for the
reloading of SRTP keys in re-INVITE transfer scenarios, this patch
addresses the more common case where a new key is requested within 
the context of a current SIP dialog.  This can occur, for example, when
certain phones request a SIP hold.

Previously, once a dialog was associated with an SRTP object, any
subsequent attempt to process crypto keys in any SDP offer - either
the current one or a new offer in a new SIP request - were ignored.  This
patch changes this behavior to only ignore subsequent crypto keys within
the current SDP offer, but allows future SDP offers to change the keys.

(issue ASTERISK-19253)
Reported by: Thomas Arimont
Tested by: Thomas Arimont

Review: https://reviewboard.asteriskorg/r/1885/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@364203 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -8903,6 +8903,7 @@ static int process_sdp(struct sip_pvt *p, struct sip_request *req, int t38action
 		int video = FALSE;
 		int image = FALSE;
 		int text = FALSE;
+		int processed_crypto = FALSE;
 		char protocol[5] = {0,};
 		int x;
 
@@ -9077,28 +9078,34 @@ static int process_sdp(struct sip_pvt *p, struct sip_request *req, int t38action
 			case 'a':
 				/* Audio specific scanning */
 				if (audio) {
-					if (process_sdp_a_sendonly(value, &sendonly))
+					if (process_sdp_a_sendonly(value, &sendonly)) {
 						processed = TRUE;
-					else if (process_crypto(p, p->rtp, &p->srtp, value))
+					} else if (!processed_crypto && process_crypto(p, p->rtp, &p->srtp, value)) {
+						processed_crypto = TRUE;
 						processed = TRUE;
-					else if (process_sdp_a_audio(value, p, &newaudiortp, &last_rtpmap_codec))
+					} else if (process_sdp_a_audio(value, p, &newaudiortp, &last_rtpmap_codec)) {
 						processed = TRUE;
+					}
 				}
 				/* Video specific scanning */
 				else if (video) {
-					if (process_sdp_a_sendonly(value, &vsendonly))
+					if (process_sdp_a_sendonly(value, &vsendonly)) {
 						processed = TRUE;
-					else if (process_crypto(p, p->vrtp, &p->vsrtp, value))
+					} else if (!processed_crypto && process_crypto(p, p->vrtp, &p->vsrtp, value)) {
+						processed_crypto = TRUE;
 						processed = TRUE;
-					else if (process_sdp_a_video(value, p, &newvideortp, &last_rtpmap_codec))
+					} else if (process_sdp_a_video(value, p, &newvideortp, &last_rtpmap_codec)) {
 						processed = TRUE;
+					}
 				}
 				/* Text (T.140) specific scanning */
 				else if (text) {
-					if (process_sdp_a_text(value, p, &newtextrtp, red_fmtp, &red_num_gen, red_data_pt, &last_rtpmap_codec))
+					if (process_sdp_a_text(value, p, &newtextrtp, red_fmtp, &red_num_gen, red_data_pt, &last_rtpmap_codec)) {
 						processed = TRUE;
-					else if (process_crypto(p, p->trtp, &p->tsrtp, value))
+					} else if (!processed_crypto && process_crypto(p, p->trtp, &p->tsrtp, value)) {
+						processed_crypto = TRUE;
 						processed = TRUE;
+					}
 				}
 				/* Image (T.38 FAX) specific scanning */
 				else if (image) {
@@ -29623,12 +29630,6 @@ static int process_crypto(struct sip_pvt *p, struct ast_rtp_instance *rtp, struc
 		}
 	}
 
-	/* For now, when we receive an INVITE just take the first successful crypto line */
-	if ((*srtp)->crypto && !ast_test_flag(&p->flags[0], SIP_OUTGOING)) {
-		ast_debug(3, "We've already processed a crypto attribute, skipping '%s'\n", a);
-		return FALSE;
-	}
-
 	if (!(*srtp)->crypto && !((*srtp)->crypto = sdp_crypto_setup())) {
 		return FALSE;
 	}