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    Subject[PATCH 1/3] wait_task_stopped: don't use task_pid_nr_ns() lockless
    wait_task_stopped(WNOWAIT) does task_pid_nr_ns() without tasklist/rcu lock,
    we can read an already freed memory. Use the cached pid_t value.

    Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

    --- 24/kernel/exit.c~1_PID 2007-11-16 18:12:44.000000000 +0300
    +++ 24/kernel/exit.c 2007-11-16 18:13:54.000000000 +0300
    @@ -1357,7 +1357,7 @@ static int wait_task_stopped(struct task
    int __user *stat_addr, struct rusage __user *ru)
    {
    int retval, exit_code;
    - struct pid_namespace *ns;
    + pid_t pid;

    if (!p->exit_code)
    return 0;
    @@ -1376,12 +1376,11 @@ static int wait_task_stopped(struct task
    * keep holding onto the tasklist_lock while we call getrusage and
    * possibly take page faults for user memory.
    */
    - ns = current->nsproxy->pid_ns;
    + pid = task_pid_nr_ns(p, current->nsproxy->pid_ns);
    get_task_struct(p);
    read_unlock(&tasklist_lock);

    if (unlikely(noreap)) {
    - pid_t pid = task_pid_nr_ns(p, ns);
    uid_t uid = p->uid;
    int why = (p->ptrace & PT_PTRACED) ? CLD_TRAPPED : CLD_STOPPED;

    @@ -1451,11 +1450,11 @@ bail_ref:
    if (!retval && infop)
    retval = put_user(exit_code, &infop->si_status);
    if (!retval && infop)
    - retval = put_user(task_pid_nr_ns(p, ns), &infop->si_pid);
    + retval = put_user(pid, &infop->si_pid);
    if (!retval && infop)
    retval = put_user(p->uid, &infop->si_uid);
    if (!retval)
    - retval = task_pid_nr_ns(p, ns);
    + retval = pid;
    put_task_struct(p);

    BUG_ON(!retval);
    -
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