The patch below does not apply to the 5.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From dfea9fce29fda6f2f91161677e0e0d9b671bc099 Mon Sep 17 00:00:00 2001

From: Pavel Begunkov asml.silence@gmail.com Date: Fri, 18 Dec 2020 13:12:21 +0000 Subject: [PATCH] io_uring: close a small race gap for files cancel

The purpose of io_uring_cancel_files() is to wait for all requests matching ->files to go/be cancelled. We should first drop files of a request in io_req_drop_files() and only then make it undiscoverable for io_uring_cancel_files.

First drop, then delete from list. It's ok to leave req->id->files dangling, because it's not dereferenced by cancellation code, only compared against. It would potentially go to sleep and be awaken by following in io_req_drop_files() wake_up().

Fixes: 0f2122045b946 ("io_uring: don't rely on weak ->files references") Cc: stable@vger.kernel.org # 5.5+ Signed-off-by: Pavel Begunkov asml.silence@gmail.com Signed-off-by: Jens Axboe axboe@kernel.dk

diff --git a/fs/io_uring.c b/fs/io_uring.c index 8cf6f22afc5e..b74957856e68 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -6098,15 +6098,15 @@ static void io_req_drop_files(struct io_kiocb *req) struct io_uring_task *tctx = req->task->io_uring; unsigned long flags;

+ put_files_struct(req->work.identity->files); + put_nsproxy(req->work.identity->nsproxy); spin_lock_irqsave(&ctx->inflight_lock, flags); list_del(&req->inflight_entry); - if (atomic_read(&tctx->in_idle)) - wake_up(&tctx->wait); spin_unlock_irqrestore(&ctx->inflight_lock, flags); req->flags &= ~REQ_F_INFLIGHT; - put_files_struct(req->work.identity->files); - put_nsproxy(req->work.identity->nsproxy); req->work.flags &= ~IO_WQ_WORK_FILES; + if (atomic_read(&tctx->in_idle)) + wake_up(&tctx->wait); }

static void __io_clean_op(struct io_kiocb *req)