On Thu, 2010-12-16 at 08:53 +0100, Mike Galbraith wrote: > On Wed, 2010-12-15 at 18:50 +0100, Oleg Nesterov wrote: > Thanks again for your excellent eyeballs. The below should plug that > hole, no? (hope so, seems pointless to lock movement) I'd also have to disable interrupts though, so may as well just lock it. I didn't do the -ESRCH or no display bit. As far as autogroup is concerned, if you couldn't lock, it's history, so belongs to init. sched: 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@xxxxxxxxxx> Signed-off-by: Mike Galbraith <efault@xxxxxx> diff --git a/kernel/sched_autogroup.c b/kernel/sched_autogroup.c index 57a7ac2..c80fedc 100644 --- a/kernel/sched_autogroup.c +++ b/kernel/sched_autogroup.c @@ -41,6 +41,20 @@ static inline struct autogroup *autogroup_kref_get(struct autogroup *ag) return ag; } +static inline struct autogroup *autogroup_task_get(struct task_struct *p) +{ + struct autogroup *ag; + unsigned long flags; + + if (!lock_task_sighand(p, &flags)) + return autogroup_kref_get(&autogroup_default); + + ag = autogroup_kref_get(p->signal->autogroup); + unlock_task_sighand(p, &flags); + + return ag; +} + static inline struct autogroup *autogroup_create(void) { struct autogroup *ag = kzalloc(sizeof(*ag), GFP_KERNEL); @@ -149,11 +163,7 @@ EXPORT_SYMBOL(sched_autogroup_detach); void sched_autogroup_fork(struct signal_struct *sig) { - struct task_struct *p = current; - - spin_lock_irq(&p->sighand->siglock); - sig->autogroup = autogroup_kref_get(p->signal->autogroup); - spin_unlock_irq(&p->sighand->siglock); + sig->autogroup = autogroup_task_get(current); } void sched_autogroup_exit(struct signal_struct *sig) @@ -172,7 +182,6 @@ __setup("noautogroup", setup_autogroup); #ifdef CONFIG_PROC_FS -/* Called with siglock held. */ int proc_sched_autogroup_set_nice(struct task_struct *p, int *nice) { static unsigned long next = INITIAL_JIFFIES; @@ -194,7 +203,7 @@ int proc_sched_autogroup_set_nice(struct task_struct *p, int *nice) return -EAGAIN; next = HZ / 10 + jiffies; - ag = autogroup_kref_get(p->signal->autogroup); + ag = autogroup_task_get(p); down_write(&ag->lock); err = sched_group_set_shares(ag->tg, prio_to_weight[*nice + 20]); @@ -209,7 +218,7 @@ int proc_sched_autogroup_set_nice(struct task_struct *p, int *nice) void proc_sched_autogroup_show_task(struct task_struct *p, struct seq_file *m) { - struct autogroup *ag = autogroup_kref_get(p->signal->autogroup); + struct autogroup *ag = autogroup_task_get(p); down_read(&ag->lock); seq_printf(m, "/autogroup-%ld nice %d\n", ag->id, ag->nice); -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html