io_uring: Fix incorrect sizeof operator for copy_from_user call

Static analysis is warning that the sizeof being used is should be
of *data->tags[i] and not data->tags[i]. Although these are the same
size on 64 bit systems it is not a portable assumption to assume
this is true for all cases.  Fix this by using a temporary pointer
tag_slot to make the code a clearer.

Addresses-Coverity: ("Sizeof not portable")
Fixes: d878c816 ("io_uring: hide rsrc tag copy into generic helpers")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/20210615130011.57387-1-colin.king@canonical.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -7230,8 +7230,10 @@ static int io_rsrc_data_alloc(struct io_ring_ctx *ctx, rsrc_put_fn *do_put,
 	if (utags) {
 		ret = -EFAULT;
 		for (i = 0; i < nr; i++) {
-			if (copy_from_user(io_get_tag_slot(data, i), &utags[i],
-					   sizeof(data->tags[i])))
+			u64 *tag_slot = io_get_tag_slot(data, i);
+
+			if (copy_from_user(tag_slot, &utags[i],
+					   sizeof(*tag_slot)))
 				goto fail;
 		}
 	}