NFSv4: Fix potential Oops in decode_op_map()

The return value of xdr_inline_decode() is not being checked, leading to
a potential Oops. Just replace the open coded array decode with the
generic XDR version.

Reported-by: <rtm@csail.mit.edu>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/nfs4xdr.c

@@ -5575,20 +5575,9 @@ static int decode_secinfo_no_name(struct xdr_stream *xdr, struct nfs4_secinfo_re
 
 static int decode_op_map(struct xdr_stream *xdr, struct nfs4_op_map *op_map)
 {
-	__be32 *p;
-	uint32_t bitmap_words;
-	unsigned int i;
-
-	p = xdr_inline_decode(xdr, 4);
-	if (!p)
-		return -EIO;
-	bitmap_words = be32_to_cpup(p++);
-	if (bitmap_words > NFS4_OP_MAP_NUM_WORDS)
+	if (xdr_stream_decode_uint32_array(xdr, op_map->u.words,
+					   ARRAY_SIZE(op_map->u.words)) < 0)
 		return -EIO;
-	p = xdr_inline_decode(xdr, 4 * bitmap_words);
-	for (i = 0; i < bitmap_words; i++)
-		op_map->u.words[i] = be32_to_cpup(p++);
-
 	return 0;
 }