From: Jens Axboe axboe@kernel.dk
commit 6d816e088c359866f9867057e04f244c608c42fe upstream.
We're holding the request reference, but we need to go one higher to ensure that the ctx remains valid after the request has finished. If the ring is closed with pending task_work inflight, and the given io_kiocb finishes sync during issue, then we need a reference to the ring itself around the task_work execution cycle.
Cc: stable@vger.kernel.org # v5.7+ Reported-by: syzbot+9b260fc33297966f5a8e@syzkaller.appspotmail.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/io_uring.c | 6 ++++++ 1 file changed, 6 insertions(+)
--- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -4214,6 +4214,8 @@ static int __io_async_wake(struct io_kio tsk = req->task; req->result = mask; init_task_work(&req->task_work, func); + percpu_ref_get(&req->ctx->refs); + /* * If this fails, then the task is exiting. When a task exits, the * work gets canceled, so just cancel this request as well instead @@ -4313,6 +4315,7 @@ static void io_poll_task_handler(struct static void io_poll_task_func(struct callback_head *cb) { struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work); + struct io_ring_ctx *ctx = req->ctx; struct io_kiocb *nxt = NULL;
io_poll_task_handler(req, &nxt); @@ -4323,6 +4326,7 @@ static void io_poll_task_func(struct cal __io_queue_sqe(nxt, NULL); mutex_unlock(&ctx->uring_lock); } + percpu_ref_put(&ctx->refs); }
static int io_poll_double_wake(struct wait_queue_entry *wait, unsigned mode, @@ -4439,6 +4443,7 @@ static void io_async_task_func(struct ca
if (io_poll_rewait(req, &apoll->poll)) { spin_unlock_irq(&ctx->completion_lock); + percpu_ref_put(&ctx->refs); return; }
@@ -4476,6 +4481,7 @@ end_req:
kfree(apoll->double_poll); kfree(apoll); + percpu_ref_put(&ctx->refs); }
static int io_async_wake(struct wait_queue_entry *wait, unsigned mode, int sync,