From 581b8394977a701c7b673acbd1c5c27eb07455da Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Mon, 22 Apr 2019 10:23:23 -0600 Subject: [PATCH 0458/2944] io_uring: fail io_uring_register(2) on a dying io_uring instance commit 35fa71a030caa50458a043560d4814ea9bcd639f upstream. 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: b19062a56726 ("io_uring: fix possible deadlock between io_uring_{enter,register}") Reported-by: syzbot Signed-off-by: Jens Axboe Signed-off-by: Joseph Qi Reviewed-by: Jeffle Xu Acked-by: Caspar Zhang --- fs/io_uring.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/fs/io_uring.c b/fs/io_uring.c index f0c15a7..ce1c922 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -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); /* -- 1.8.3.1