[PATCH] io_uring: fix fs cleanup on cqe overflow

[PATCH] io_uring: fix fs cleanup on cqe overflow

[Pavel Begunkov]

If completion queue overflow happened, __io_cqring_fill_event() will
update req->cflags, which is in a union with req->work and happend to
be aliased to req->work.fs. Following io_free_req() ->
io_req_work_drop_env() may get a bunch of different problems (miscount
fs->users, segfault, etc) on cleaning @fs.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---

P.S. never tried to reproduce the issue

 fs/io_uring.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 21e1c69b9c43..be65eda059ac 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -608,6 +608,7 @@ struct io_kiocb {
 	};
 
 	struct io_async_ctx		*io;
+	int				cflags;
 	bool				needs_fixed_file;
 	u8				opcode;
 
@@ -638,7 +639,6 @@ struct io_kiocb {
 			struct callback_head	task_work;
 			struct hlist_node	hash_node;
 			struct async_poll	*apoll;
-			int			cflags;
 		};
 		struct io_wq_work	work;
 	};
-- 
2.24.0

Re: [PATCH] io_uring: fix fs cleanup on cqe overflow

[Jens Axboe]

On 4/8/20 10:17 PM, Pavel Begunkov wrote:
> If completion queue overflow happened, __io_cqring_fill_event() will
> update req->cflags, which is in a union with req->work and happend to
> be aliased to req->work.fs. Following io_free_req() ->
> io_req_work_drop_env() may get a bunch of different problems (miscount
> fs->users, segfault, etc) on cleaning @fs.

Good catch, applied.

-- 
Jens Axboe