linux-kernel - [PATCH 5.7 435/477] io_uring: fix possible race condition against REQ_F_NEED

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Date:   Tue, 23 Jun 2020 21:57:12 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Xiaoguang Wang <xiaoguang.wang@...ux.alibaba.com>,
        Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 5.7 435/477] io_uring: fix possible race condition against REQ_F_NEED_CLEANUP

From: Xiaoguang Wang <xiaoguang.wang@...ux.alibaba.com>

[ Upstream commit 6f2cc1664db20676069cff27a461ccc97dbfd114 ]

In io_read() or io_write(), when io request is submitted successfully,
it'll go through the below sequence:

    kfree(iovec);
    req->flags &= ~REQ_F_NEED_CLEANUP;
    return ret;

But clearing REQ_F_NEED_CLEANUP might be unsafe. The io request may
already have been completed, and then io_complete_rw_iopoll()
and io_complete_rw() will be called, both of which will also modify
req->flags if needed. This causes a race condition, with concurrent
non-atomic modification of req->flags.

To eliminate this race, in io_read() or io_write(), if io request is
submitted successfully, we don't remove REQ_F_NEED_CLEANUP flag. If
REQ_F_NEED_CLEANUP is set, we'll leave __io_req_aux_free() to the
iovec cleanup work correspondingly.

Cc: stable@...r.kernel.org
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@...ux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/io_uring.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2614,8 +2614,8 @@ copy_iov:
 		}
 	}
 out_free:
-	kfree(iovec);
-	req->flags &= ~REQ_F_NEED_CLEANUP;
+	if (!(req->flags & REQ_F_NEED_CLEANUP))
+		kfree(iovec);
 	return ret;
 }

@@ -2737,8 +2737,8 @@ copy_iov:
 		}
 	}
 out_free:
-	req->flags &= ~REQ_F_NEED_CLEANUP;
-	kfree(iovec);
+	if (!(req->flags & REQ_F_NEED_CLEANUP))
+		kfree(iovec);
 	return ret;
 }