linux-kernel - [PATCH 3/3] io_uring: Fix race for sqes with userspace

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Message-Id: <cfb7206ba1ac48615fd705ac74fc2d554a0c5422.1571991701.git.asml.silence@gmail.com>
Date:   Fri, 25 Oct 2019 12:31:31 +0300
From:   "Pavel Begunkov (Silence)" <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Pavel Begunkov <asml.silence@...il.com>
Subject: [PATCH 3/3] io_uring: Fix race for sqes with userspace

From: Pavel Begunkov <asml.silence@...il.com>

io_ring_submit() finalises with
1. io_commit_sqring(), which releases sqes to the userspace
2. Then calls to io_queue_link_head(), accessing released head's sqe

Reorder them.

Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
---
 fs/io_uring.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 949c82a40d16..32f6598ecae9 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2795,13 +2795,14 @@ static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
 		submit++;
 		io_submit_sqe(ctx, &s, statep, &link);
 	}
-	io_commit_sqring(ctx);
 
 	if (link)
 		io_queue_link_head(ctx, link, &link->submit, shadow_req);
 	if (statep)
 		io_submit_state_end(statep);
 
+	io_commit_sqring(ctx);
+
 	return submit;
 }
 
-- 
2.23.0