Commit 35fa71a0 authored Apr 22, 2019 by Jens Axboe

io_uring: fail io_uring_register(2) on a dying io_uring instance

If we have multiple threads doing io_uring_register(2) on an io_uring
fd, then we can potentially try and kill the percpu reference while
someone else has already killed it.

Prevent this race by failing io_uring_register(2) if the ref is marked
dying. This is safe since we're inside the io_uring mutex.

Fixes: b19062a5 ("io_uring: fix possible deadlock between io_uring_{enter,register}")
Reported-by: syzbot <syzbot+10d25e23199614b7721f@syzkaller.appspotmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 085b7755

fs/io_uring.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -2934,6 +2934,14 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
		{
		int ret;

		/*
		* We're inside the ring mutex, if the ref is already dying, then
		* someone else killed the ctx or is already going through
		* io_uring_register().
		*/
		if (percpu_ref_is_dying(&ctx->refs))
		return -ENXIO;

		percpu_ref_kill(&ctx->refs);

		/*