io_uring: fix possible race condition against REQ_F_NEED_CLEANUP

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@vger.kernel.org
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 2038d52..a78201b 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2670,8 +2670,8 @@ copy_iov:
                }
        }
 out_free:
-       kfree(iovec);
-       req->flags &= ~REQ_F_NEED_CLEANUP;
+       if (!(req->flags & REQ_F_NEED_CLEANUP))
+               kfree(iovec);
        return ret;
 }
 
@@ -2793,8 +2793,8 @@ copy_iov:
                }
        }
 out_free:
-       req->flags &= ~REQ_F_NEED_CLEANUP;
-       kfree(iovec);
+       if (!(req->flags & REQ_F_NEED_CLEANUP))
+               kfree(iovec);
        return ret;
 }