[PATCH 5.9 15/74] io_uring: Fix XArray usage in io_uring_add_task_file

Greg Kroah-Hartman
2020-10-31T11:48:51Z

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

commit 236434c3438c4da3dfbd6aeeab807577b85e951a upstream.

The xas_store() wasn't paired with an xas_nomem() loop, so if it couldn't
allocate memory using GFP_NOWAIT, it would leak the reference to the file
descriptor. Also the node pointed to by the xas could be freed between
the call to xas_load() under the rcu_read_lock() and the acquisition of
the xa_lock.

It's easier to just use the normal xa_load/xa_store interface here.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
[axboe: fix missing assign after alloc, cur_uring -> tctx rename]
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/io_uring.c | 21 +++++++++------------
1 file changed, 9 insertions(+), 12 deletions(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -8336,27 +8336,24 @@ static void io_uring_cancel_task_request
*/
static int io_uring_add_task_file(struct file *file)
{
- if (unlikely(!current->io_uring)) {
+ struct io_uring_task *tctx = current->io_uring;
+
+ if (unlikely(!tctx)) {
int ret;

ret = io_uring_alloc_task_context(current);
if (unlikely(ret))
return ret;
+ tctx = current->io_uring;
}
- if (current->io_uring->last != file) {
- XA_STATE(xas, &current->io_uring->xa, (unsigned long) file);
- void *old;
+ if (tctx->last != file) {
+ void *old = xa_load(&tctx->xa, (unsigned long)file);

- rcu_read_lock();
- old = xas_load(&xas);
- if (old != file) {
+ if (!old) {
get_file(file);
- xas_lock(&xas);
- xas_store(&xas, file);
- xas_unlock(&xas);
+ xa_store(&tctx->xa, (unsigned long)file, file, GFP_KERNEL);
}
- rcu_read_unlock();
- current->io_uring->last = file;
+ tctx->last = file;
}

return 0;