Don't feed anything but regular iovec's to blk_rq_map_user_iov

commit a0ac402c upstream.

In theory we could map other things, but there's a reason that function
is called "user_iov".  Using anything else (like splice can do) just
confuses it.
Reported-and-tested-by: Johannes Thumshirn <jthumshirn@suse.de>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

block/blk-map.c

@@ -90,6 +90,9 @@ int blk_rq_map_user_iov(struct request_queue *q, struct request *rq,
 	if (!iter || !iter->count)
 		return -EINVAL;
 
+	if (!iter_is_iovec(iter))
+		return -EINVAL;
+
 	iov_for_each(iov, i, *iter) {
 		unsigned long uaddr = (unsigned long) iov.iov_base;