NFSv4.1 enforce rootpath check in fs_location query

In commit 4ca9f31a ("NFSv4.1 test and add 4.1 trunking transport"),
we introduce the ability to query the NFS server for possible trunking
locations of the existing filesystem. However, we never checked the
returned file system path for these alternative locations. According
to the RFC, the server can say that the filesystem currently known
under "fs_root" of fs_location also resides under these server
locations under the following "rootpath" pathname. The client cannot
handle trunking a filesystem that reside under different location
under different paths other than what the main path is. This patch
enforces the check that fs_root path and rootpath path in fs_location
reply is the same.

Fixes: 4ca9f31a ("NFSv4.1 test and add 4.1 trunking transport")
Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/nfs4proc.c

@@ -4023,6 +4023,23 @@ static void test_fs_location_for_trunking(struct nfs4_fs_location *location,
 	}
 }
 
+static bool _is_same_nfs4_pathname(struct nfs4_pathname *path1,
+				   struct nfs4_pathname *path2)
+{
+	int i;
+
+	if (path1->ncomponents != path2->ncomponents)
+		return false;
+	for (i = 0; i < path1->ncomponents; i++) {
+		if (path1->components[i].len != path2->components[i].len)
+			return false;
+		if (memcmp(path1->components[i].data, path2->components[i].data,
+				path1->components[i].len))
+			return false;
+	}
+	return true;
+}
+
 static int _nfs4_discover_trunking(struct nfs_server *server,
 				   struct nfs_fh *fhandle)
 {
@@ -4056,9 +4073,13 @@ static int _nfs4_discover_trunking(struct nfs_server *server,
 	if (status)
 		goto out_free_3;
 
-	for (i = 0; i < locations->nlocations; i++)
+	for (i = 0; i < locations->nlocations; i++) {
+		if (!_is_same_nfs4_pathname(&locations->fs_path,
+					&locations->locations[i].rootpath))
+			continue;
 		test_fs_location_for_trunking(&locations->locations[i], clp,
 					      server);
+	}
 out_free_3:
 	kfree(locations->fattr);
 out_free_2: