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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>
This commit is contained in:
Xiaoguang Wang 2020-06-18 15:01:56 +08:00 committed by Jens Axboe
parent 56952e91ac
commit 6f2cc1664d
1 changed files with 4 additions and 4 deletions
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8
fs/io_uring.c
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@ -2670,8 +2670,8 @@ copy_iov:
} }
} }
out_free: out_free:
kfree(iovec); if (!(req->flags & REQ_F_NEED_CLEANUP))
req->flags &= ~REQ_F_NEED_CLEANUP; kfree(iovec);
return ret; return ret;
} }
@ -2793,8 +2793,8 @@ copy_iov:
} }
} }
out_free: out_free:
req->flags &= ~REQ_F_NEED_CLEANUP; if (!(req->flags & REQ_F_NEED_CLEANUP))
kfree(iovec); kfree(iovec);
return ret; return ret;
} }