SUNRPC: Fix integer overflow in decode_rc_list()

The math in "rc_list->rcl_nrefcalls * 2 * sizeof(uint32_t)" could have an
integer overflow.  Add bounds checking on rc_list->rcl_nrefcalls to fix
that.

Fixes: 4aece6a1 ("nfs41: cb_sequence xdr implementation")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>

fs/nfs/callback_xdr.c

@@ -375,6 +375,8 @@ static __be32 decode_rc_list(struct xdr_stream *xdr,
 
 	rc_list->rcl_nrefcalls = ntohl(*p++);
 	if (rc_list->rcl_nrefcalls) {
+		if (unlikely(rc_list->rcl_nrefcalls > xdr->buf->len))
+			goto out;
 		p = xdr_inline_decode(xdr,
 			     rc_list->rcl_nrefcalls * 2 * sizeof(uint32_t));
 		if (unlikely(p == NULL))