[PATCH 5.7 435/477] io_uring: fix possible race condition against REQ_F_NEED_CLEANUP

[Greg Kroah-Hartman]

From: Xiaoguang Wang <xiaoguang.w...@linux.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: sta...@vger.kernel.org
Signed-off-by: Xiaoguang Wang <xiaoguang.w...@linux.alibaba.com>
Signed-off-by: Jens Axboe <ax...@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.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;
 }