zrtp: Fix race condition in performing DH

include/uvgrtp/util.hh

@@ -125,8 +125,11 @@ typedef enum RTP_FLAGS {
 enum RTP_CTX_ENABLE_FLAGS {
     RCE_NO_FLAGS                  = 0,
 
-    /* Obsolete */
+    // Obsolete flags
     RCE_SYSTEM_CALL_DISPATCHER    = 0,
+    RCE_NO_H26X_INTRA_DELAY = 0,
+    RCE_NO_H26X_SCL = 0,
+    RCE_H26X_NO_DEPENDENCY_ENFORCEMENT = 0,
 
     /** Use SRTP for this connection */
     RCE_SRTP                      = 1,
@@ -151,21 +154,12 @@ enum RTP_CTX_ENABLE_FLAGS {
      * with RCE_SRTP_KMNGMNT_ZRTP */
     RCE_SRTP_KMNGMNT_USER         = 1 << 2,
 
-    /** Obsolete */
-    RCE_NO_H26X_INTRA_DELAY       = 0,
-
-    /** Obsolete */
-    RCE_NO_H26X_SCL               = 0,
-
     /** By default, the RTP packet payload does not include the start code prefixes. 
      * Use this flag to prepend the 4-byte start code (0x00000001) to each received
      * H26x frame, so there is no difference with sender input. Recommended in 
      * most cases. */
     RCE_H26X_PREPEND_SC           = 1 << 3,
 
-    /** Obsolete */
-    RCE_H26X_NO_DEPENDENCY_ENFORCEMENT = 0,
-
     /** Use this flag to discard inter frames that don't have their previous dependencies
         arrived. Does not work if the dependencies are not in monotonic order. */
     RCE_H26X_DEPENDENCY_ENFORCEMENT = 1 << 4,
@@ -227,9 +221,12 @@ enum RTP_CTX_ENABLE_FLAGS {
     /** Use 256-bit keys with SRTP */
     RCE_SRTP_KEYSIZE_256          = 1 << 14,
 
-    RCE_LAST                      = 1 << 15,
+    RCE_ZRTP_MULTISTREAM_NO_DH    = 1 << 16,
+
+    RCE_LAST                      = 1 << 17,
 };
 
+
 /**
  * \enum RTP_CTX_CONFIGURATION_FLAGS
  *

src/media_stream.cc

@@ -261,7 +261,9 @@ rtp_error_t uvgrtp::media_stream::init(std::shared_ptr<uvgrtp::zrtp> zrtp)
 
     rtp_ = std::shared_ptr<uvgrtp::rtp> (new uvgrtp::rtp(fmt_));
 
-    if ((ret = zrtp->init(rtp_->get_ssrc(), socket_, addr_out_)) != RTP_OK) {
+    bool perform_dh = !(rce_flags_ & RCE_ZRTP_MULTISTREAM_NO_DH);
+
+    if ((ret = zrtp->init(rtp_->get_ssrc(), socket_, addr_out_, perform_dh)) != RTP_OK) {
         UVG_LOG_WARN("Failed to initialize ZRTP for media stream!");
         return free_resources(ret);
     }

src/zrtp.cc

@@ -616,13 +616,41 @@ rtp_error_t uvgrtp::zrtp::initiator_finalize_session()
     return RTP_TIMEOUT;
 }
 
-rtp_error_t uvgrtp::zrtp::init(uint32_t ssrc, std::shared_ptr<uvgrtp::socket> socket, sockaddr_in& addr)
+rtp_error_t uvgrtp::zrtp::init(uint32_t ssrc, std::shared_ptr<uvgrtp::socket> socket, sockaddr_in& addr, bool perform_dh)
 {
-    std::lock_guard<std::mutex> lock(zrtp_mtx_);
+    rtp_error_t ret = RTP_OK;
 
-    if (!initialized_)
-        return init_dhm(ssrc, socket, addr);
-    return init_msm(ssrc, socket, addr);
+    if (perform_dh) 
+    {
+        zrtp_mtx_.lock();
+        
+        if (initialized_)
+        {
+            UVG_LOG_WARN("ZRTP multistream mode not used. Please use RCE_ZRTP_MULTISTREAM_NO_DH flag " \
+                "to select which streams should not perform DH");
+        }
+
+        // perform Diffie-Helmann (DH)
+        ret = init_dhm(ssrc, socket, addr);
+        zrtp_mtx_.unlock();
+    }
+    else
+    {
+        if (!initialized_)
+        {
+            UVG_LOG_DEBUG("Sleeping a non-DH performing stream until DH has finished");
+        }
+
+        while (!initialized_)
+        {
+            std::this_thread::sleep_for(std::chrono::milliseconds(5));
+        }
+
+        // multistream mode
+        ret = init_msm(ssrc, socket, addr);
+    }
+
+    return ret;
 }
 
 rtp_error_t uvgrtp::zrtp::init_dhm(uint32_t ssrc, std::shared_ptr<uvgrtp::socket> socket, sockaddr_in& addr)

src/zrtp.hh

@@ -42,7 +42,7 @@ namespace uvgrtp {
              *
              * Return RTP_OK on success
              * Return RTP_TIMEOUT if remote did not send messages in timely manner */
-            rtp_error_t init(uint32_t ssrc, std::shared_ptr<uvgrtp::socket> socket, sockaddr_in& addr);
+            rtp_error_t init(uint32_t ssrc, std::shared_ptr<uvgrtp::socket> socket, sockaddr_in& addr, bool perform_dh);
 
             /* Get SRTP keys for the session that was just initialized
              *