Commit 4faa9996 authored May 23, 2018 by Al Viro

fix io_destroy()/aio_complete() race

If io_destroy() gets to cancelling everything that can be cancelled and
gets to kiocb_cancel() calling the function driver has left in ->ki_cancel,
it becomes vulnerable to a race with IO completion. At that point req
is already taken off the list and aio_complete() does *NOT* spin until
we (in free_ioctx_users()) releases ->ctx_lock. As the result, it proceeds
to kiocb_free(), freing req just it gets passed to ->ki_cancel().

Fix is simple - remove from the list after the call of kiocb_cancel(). All
instances of ->ki_cancel() already have to cope with the being called with
iocb still on list - that's what happens in io_cancel(2).

Cc: stable@kernel.org
Fixes: 0460fef2 "aio: use cancellation list lazily"
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

parent baf10564

fs/aio.c

+1 −2

Original line number	Diff line number	Diff line
		@@ -634,9 +634,8 @@ static void free_ioctx_users(struct percpu_ref *ref)
		while (!list_empty(&ctx->active_reqs)) {
		req = list_first_entry(&ctx->active_reqs,
		struct aio_kiocb, ki_list);

		list_del_init(&req->ki_list);
		kiocb_cancel(req);
		list_del_init(&req->ki_list);
		}

		spin_unlock_irq(&ctx->ctx_lock);

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