NFSv4: handle lack of clientaddr in option string

If a NFSv4 mount is attempted  with string based options, and the
option string doesn't contain a clientaddr= option, the kernel will
currently oops. Check for this situation and return a proper error.
Signed-off-by: NJeff Layton <jlayton@redhat.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/super.c

@@ -1685,6 +1685,9 @@ static int nfs4_validate_mount_data(struct nfs4_mount_data **options,
 
 		dprintk("MNTPATH: %s\n", *mntpath);
 
+		if (args.client_address == NULL)
+			goto out_no_client_address;
+
 		*ip_addr = args.client_address;
 
 		break;
@@ -1705,6 +1708,10 @@ static int nfs4_validate_mount_data(struct nfs4_mount_data **options,
 out_no_address:
 	dfprintk(MOUNT, "NFS4: mount program didn't pass remote address\n");
 	return -EINVAL;
+
+out_no_client_address:
+	dfprintk(MOUNT, "NFS4: mount program didn't pass callback address\n");
+	return -EINVAL;
 }
 
 /*