comm_join: fix CID 1323170

Enusre that the port name is always NULL-terminated.

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>

ompi/dpm/dpm.c

@@ -10,7 +10,7 @@
  *                         University of Stuttgart.  All rights reserved.
  * Copyright (c) 2004-2005 The Regents of the University of California.
  *                         All rights reserved.
- * Copyright (c) 2007-2015 Cisco Systems, Inc.  All rights reserved.
+ * Copyright (c) 2007-2018 Cisco Systems, Inc.  All rights reserved
  * Copyright (c) 2006-2009 University of Houston.  All rights reserved.
  * Copyright (c) 2009      Sun Microsystems, Inc.  All rights reserved.
  * Copyright (c) 2011-2015 Los Alamos National Security, LLC.  All rights
@@ -958,6 +958,7 @@ int ompi_dpm_open_port(char *port_name)
     r = opal_rand(&rnd);
     opal_convert_process_name_to_string(&tmp, OMPI_PROC_MY_NAME);
     snprintf(port_name, MPI_MAX_PORT_NAME-1, "%s:%u", tmp, r);
+    port_name[MPI_MAX_PORT_NAME - 1] = '\0';
     free(tmp);
     return OMPI_SUCCESS;
 }

ompi/mpi/c/comm_join.c

@@ -13,7 +13,7 @@
  *                         All rights reserved.
  * Copyright (c) 2015      Research Organization for Information Science
  *                         and Technology (RIST). All rights reserved.
- * Copyright (c) 2015 Cisco Systems, Inc.  All rights reserved.
+ * Copyright (c) 2015-2018 Cisco Systems, Inc.  All rights reserved
  * $COPYRIGHT$
  *
  * Additional copyrights may follow
@@ -110,9 +110,6 @@ int MPI_Comm_join(int fd, MPI_Comm *intercomm)
         send_first = true;
     }
 
-    /* ensure the port name is NULL terminated */
-    memset(port_name, 0, MPI_MAX_PORT_NAME);
-
     /* Assumption: socket_send should not block, even if the socket
        is not configured to be non-blocking, because the message length are
        so short. */
@@ -120,16 +117,21 @@ int MPI_Comm_join(int fd, MPI_Comm *intercomm)
     /* we will only use the send_first proc's port name,
      * so pass it to the recv_first participant */
     if (send_first) {
-        /* open a port */
+        // The port_name that we get back will be \0-terminated.  The
+        // strlen+\0 will be <= MPI_MAX_PORT_NAME characters.
         if (OMPI_SUCCESS != (rc = ompi_dpm_open_port(port_name))) {
             goto error;
         }
+        // Send the strlen+1 so that we both send the \0 and the
+        // receiver receives the \0.
         llen   = (uint32_t)(strlen(port_name)+1);
         len    = htonl(llen);
         ompi_socket_send( fd, (char *) &len, sizeof(uint32_t));
         ompi_socket_send (fd, port_name, llen);
     } else {
         ompi_socket_recv (fd, (char *) &rlen, sizeof(uint32_t));
+        // The lrlen that we receive will be the strlen+1 (to account
+        // for \0), and will be <= MPI_MAX_PORT_NAME.
         lrlen  = ntohl(rlen);
         ompi_socket_recv (fd, port_name, lrlen);
     }