fix: re-use of bound connections

When asked to bind the local end of a connection when doing a request,
the code will now disqualify other existing connections from re-use even
if they are connected to the correct remote host.

This will also affect which connections that can be used for pipelining,
so that only connections that aren't bound or bound to the same
device/port you're asking for will be considered.

TODO-RELEASE

@@ -1,8 +1,6 @@
 To be addressed in 7.21.5
 =========================
 
-272 - re-using connections bound to local port
-
 275 - Introduce a way to avoid sending USER for FTP connections
 
 278 - "Configure  $as_echo does not work"

lib/url.c

@@ -2606,7 +2606,7 @@ static void conn_free(struct connectdata *conn)
   Curl_safefree(conn->async.hostname);
   Curl_safefree(conn->async.os_specific);
 #endif
-
+  Curl_safefree(conn->localdev);
   Curl_free_ssl_config(&conn->ssl_config);
 
   free(conn); /* free all the connection oriented data */
@@ -2987,6 +2987,25 @@ ConnectionExists(struct SessionHandle *data,
          in use so we skip it */
       continue;
 
+    if(needle->localdev || needle->localport) {
+      /* If we are bound to a specific local end (IP+port), we must not re-use
+         a random other one, although if we didn't ask for a particular one we
+         can reuse one that was bound.
+
+         This comparison is a bit rough and too strict. Since the input
+         parameters can be specified in numerous ways and still end up the
+         same it would take a lot of processing to make it really accurate.
+         Instead, this matching will assume that re-uses of bound connections
+         will most likely also re-use the exact same binding parameters and
+         missing out a few edge cases shouldn't hurt anyone very much.
+      */
+      if((check->localport != needle->localport) ||
+         (check->localportrange != needle->localportrange) ||
+         !check->localdev ||
+         strcmp(check->localdev, needle->localdev))
+        continue;
+    }
+
     if(!needle->bits.httpproxy || needle->handler->flags&PROTOPT_SSL ||
        (needle->bits.httpproxy && check->bits.httpproxy &&
         needle->bits.tunnel_proxy && check->bits.tunnel_proxy &&
@@ -3568,13 +3587,24 @@ static struct connectdata *allocate_conn(struct SessionHandle *data)
   conn->data_prot = PROT_CLEAR;
 #endif
 
+  /* Store the local bind parameters that will be used for this connection */
+  if(data->set.str[STRING_DEVICE]) {
+    conn->localdev = strdup(data->set.str[STRING_DEVICE]);
+    if(!conn->localdev)
+      goto error;
+  }
+  conn->localportrange = data->set.localportrange;
+  conn->localport = data->set.localport;
+
   return conn;
   error:
+
   Curl_llist_destroy(conn->send_pipe, NULL);
   Curl_llist_destroy(conn->recv_pipe, NULL);
   Curl_llist_destroy(conn->pend_pipe, NULL);
   Curl_llist_destroy(conn->done_pipe, NULL);
   Curl_safefree(conn->master_buffer);
+  Curl_safefree(conn->localdev);
   Curl_safefree(conn);
   return NULL;
 }

lib/urldata.h

@@ -936,6 +936,16 @@ struct connectdata {
 
   long verifypeer;
   long verifyhost;
+
+  /* When this connection is created, store the conditions for the local end
+     bind. This is stored before the actual bind and before any connection is
+     made and will serve the purpose of being used for comparison reasons so
+     that subsequent bound-requested connections aren't accidentally re-using
+     wrong connections. */
+  char *localdev;
+  unsigned short localport;
+  int localportrange;
+
 };
 
 /* The end of connectdata. */