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    Subject[PATCH 56/61] fill_tgid: fix task_struct leak and possible oops
    -stable review patch.  If anyone has any objections, please let us know.
    ------------------

    From: Oleg Nesterov <oleg@tv-sign.ru>

    1. fill_tgid() forgets to do put_task_struct(first).

    2. release_task(first) can happen after fill_tgid() drops tasklist_lock,
    it is unsafe to dereference first->signal.

    This is a temporary fix, imho the locking should be reworked.

    Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
    Cc: Shailabh Nagar <nagar@watson.ibm.com>
    Cc: Balbir Singh <balbir@in.ibm.com>
    Cc: Jay Lan <jlan@sgi.com>
    Cc: <stable@kernel.org>
    Signed-off-by: Andrew Morton <akpm@osdl.org>
    Signed-off-by: Linus Torvalds <torvalds@osdl.org>
    Signed-off-by: Chris Wright <chrisw@sous-sol.org>
    ---
    kernel/taskstats.c | 15 +++++++++------
    1 file changed, 9 insertions(+), 6 deletions(-)

    --- linux-2.6.18.1.orig/kernel/taskstats.c
    +++ linux-2.6.18.1/kernel/taskstats.c
    @@ -229,14 +229,17 @@ static int fill_tgid(pid_t tgid, struct
    } else
    get_task_struct(first);

    - /* Start with stats from dead tasks */
    - spin_lock_irqsave(&first->signal->stats_lock, flags);
    - if (first->signal->stats)
    - memcpy(stats, first->signal->stats, sizeof(*stats));
    - spin_unlock_irqrestore(&first->signal->stats_lock, flags);

    tsk = first;
    read_lock(&tasklist_lock);
    + /* Start with stats from dead tasks */
    + if (first->signal) {
    + spin_lock_irqsave(&first->signal->stats_lock, flags);
    + if (first->signal->stats)
    + memcpy(stats, first->signal->stats, sizeof(*stats));
    + spin_unlock_irqrestore(&first->signal->stats_lock, flags);
    + }
    +
    do {
    if (tsk->exit_state == EXIT_ZOMBIE && thread_group_leader(tsk))
    continue;
    @@ -256,7 +259,7 @@ static int fill_tgid(pid_t tgid, struct
    * Accounting subsytems can also add calls here to modify
    * fields of taskstats.
    */
    -
    + put_task_struct(first);
    return 0;
    }

    --
    -
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