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The assumption that the fid cannot be used by any other operation is wrong. At least, nothing prevents a misbehaving client to create a file with a given fid, and to pass this fid to some other operation at the same time (ie, without waiting for the response to the creation request). The call to v9fs_path_copy() performed by the worker thread after the file was created can race with any access to the fid path performed by some other thread. This causes use-after-free issues that can be detected by ASAN with a custom 9p client. Unlike other operations that only read the fid path, v9fs_co_open2() does modify it. It should hence take the write lock. Cc: P J P <ppandit@redhat.com> Reported-by: zhibin hu <noirfate@gmail.com> Signed-off-by: Greg Kurz <groug@kaod.org>