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sched, autogroup: Fix potential access to freed memory
Oleg pointed out that the /proc interface kref_get() useage may race with the final put during autogroup_move_group(). A signal->autogroup assignment may be in flight when the /proc interface dereference, leaving them taking a reference to an already dead group. Reported-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Mike Galbraith <efault@gmx.de> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <1292508592.5940.28.camel@maggy.simson.net> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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@ -41,6 +41,20 @@ static inline struct autogroup *autogroup_kref_get(struct autogroup *ag)
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return ag;
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}
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static inline struct autogroup *autogroup_task_get(struct task_struct *p)
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{
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struct autogroup *ag;
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unsigned long flags;
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if (!lock_task_sighand(p, &flags))
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return autogroup_kref_get(&autogroup_default);
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ag = autogroup_kref_get(p->signal->autogroup);
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unlock_task_sighand(p, &flags);
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return ag;
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}
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static inline struct autogroup *autogroup_create(void)
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{
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struct autogroup *ag = kzalloc(sizeof(*ag), GFP_KERNEL);
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@ -149,11 +163,7 @@ EXPORT_SYMBOL(sched_autogroup_detach);
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void sched_autogroup_fork(struct signal_struct *sig)
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{
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struct task_struct *p = current;
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spin_lock_irq(&p->sighand->siglock);
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sig->autogroup = autogroup_kref_get(p->signal->autogroup);
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spin_unlock_irq(&p->sighand->siglock);
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sig->autogroup = autogroup_task_get(current);
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}
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void sched_autogroup_exit(struct signal_struct *sig)
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@ -172,7 +182,6 @@ __setup("noautogroup", setup_autogroup);
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#ifdef CONFIG_PROC_FS
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/* Called with siglock held. */
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int proc_sched_autogroup_set_nice(struct task_struct *p, int *nice)
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{
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static unsigned long next = INITIAL_JIFFIES;
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@ -194,7 +203,7 @@ int proc_sched_autogroup_set_nice(struct task_struct *p, int *nice)
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return -EAGAIN;
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next = HZ / 10 + jiffies;
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ag = autogroup_kref_get(p->signal->autogroup);
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ag = autogroup_task_get(p);
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down_write(&ag->lock);
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err = sched_group_set_shares(ag->tg, prio_to_weight[*nice + 20]);
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@ -209,7 +218,7 @@ int proc_sched_autogroup_set_nice(struct task_struct *p, int *nice)
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void proc_sched_autogroup_show_task(struct task_struct *p, struct seq_file *m)
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{
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struct autogroup *ag = autogroup_kref_get(p->signal->autogroup);
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struct autogroup *ag = autogroup_task_get(p);
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down_read(&ag->lock);
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seq_printf(m, "/autogroup-%ld nice %d\n", ag->id, ag->nice);
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