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    Subject[PATCH 0/2] pids: initial fixes, unsafe dereference of the special pids
    Without rcu ot tasklist lock held, it is not safe to dereference the
    result of task_session/task_pgrp. Even if the task == current.

    Because we can race with another thread doing setpgrp/setsid, and use
    the already freed/reused/unmapped memory if preempted.

    The problem is old, surprisingly it wasn't noticed before. Fortunately
    it is not very serious.

    We have a lot of users which should be fixed. This series only fixes
    sys_getsid/sys_getpgid syscalls.

    Perhaps we can (should) add rcu lock/unlock to task_xxx_vnr(), but I'm
    not sure. In any case, I think it is good to factor out pid_vnr() calls
    like these patches do.

    Oleg.



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