RDMA/ucma: Allow resolving address w/o specifying source address

The RDMA CM will select a source device and address by consulting
the routing table if no source address is passed into
rdma_resolve_address().  Userspace will ask for this by passing an
all-zero source address in the RESOLVE_IP command.  Unfortunately
the new check for non-zero address size rejects this with EINVAL,
which breaks valid userspace applications.

Fix this by explicitly allowing a zero address family for the source.

Fixes: 2975d5d ("RDMA/ucma: Check AF family prior resolving address")
Cc: <stable@vger.kernel.org>
Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/core/ucma.c

@@ -700,7 +700,7 @@ static ssize_t ucma_resolve_ip(struct ucma_file *file,
 	if (copy_from_user(&cmd, inbuf, sizeof(cmd)))
 		return -EFAULT;
 
-	if (!rdma_addr_size_in6(&cmd.src_addr) ||
+	if ((cmd.src_addr.sin6_family && !rdma_addr_size_in6(&cmd.src_addr)) ||
 	    !rdma_addr_size_in6(&cmd.dst_addr))
 		return -EINVAL;