From 6f2cc1664db20676069cff27a461ccc97dbfd114 Mon Sep 17 00:00:00 2001
From: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Date: Thu, 18 Jun 2020 15:01:56 +0800
Subject: [PATCH] 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>
---
fs/io_uring.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 2038d52c54507..a78201b961796 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2670,8 +2670,8 @@ static int io_read(struct io_kiocb *req, bool force_nonblock)
}
}
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 @@ static int io_write(struct io_kiocb *req, bool force_nonblock)
}
}
out_free:
- req->flags &= ~REQ_F_NEED_CLEANUP;
- kfree(iovec);
+ if (!(req->flags & REQ_F_NEED_CLEANUP))
+ kfree(iovec);
return ret;
}
--
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