io_uring: zero tag on rsrc removal

Automatically default rsrc tag in io_queue_rsrc_removal(), it's safer
than leaving it there and relying on the rest of the code to behave and
not use it.
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/1cf262a50df17478ea25b22494dcc19f3a80301f.1649336342.git.asml.silence@gmail.comSigned-off-by: NJens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -8927,13 +8927,15 @@ static int io_sqe_file_register(struct io_ring_ctx *ctx, struct file *file,
 static int io_queue_rsrc_removal(struct io_rsrc_data *data, unsigned idx,
 				 struct io_rsrc_node *node, void *rsrc)
 {
+	u64 *tag_slot = io_get_tag_slot(data, idx);
 	struct io_rsrc_put *prsrc;
 
 	prsrc = kzalloc(sizeof(*prsrc), GFP_KERNEL);
 	if (!prsrc)
 		return -ENOMEM;
 
-	prsrc->tag = *io_get_tag_slot(data, idx);
+	prsrc->tag = *tag_slot;
+	*tag_slot = 0;
 	prsrc->rsrc = rsrc;
 	list_add(&prsrc->list, &node->rsrc_list);
 	return 0;