vcl: zero out cmsg for recvmsg API

When msg->msg_controllen is set in recvmsg, the caller wants to receive
additional information about the messages. However, they might not
always be available. In that case, we should clear cmsg since
the caller uses CMSG_NXTHDR which might access uninitialized fields in
cmsg.

Type: fix

Change-Id: Ifdf9634bfcb1427f7ae3812014a46bfd7f4bc473
Signed-off-by: Steven Luong <sluong@cisco.com>

src/vcl/ldp.c

@@ -1748,6 +1748,7 @@ ldp_make_cmsg (vls_handle_t vlsh, struct msghdr *msg)
   struct cmsghdr *cmsg;
 
   cmsg = CMSG_FIRSTHDR (msg);
+  memset (cmsg, 0, sizeof (*cmsg));
 
   if (!vls_attr (vlsh, VPPCOM_ATTR_GET_IP_PKTINFO, (void *) &optval, &optlen))
     return 0;