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sched, autogroup: Fix potential access to freed memory

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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>
This commit is contained in:
Mike Galbraith 2010-12-16 15:09:52 +01:00 committed by Ingo Molnar
parent 6706125e29
commit 4f8219875a
1 changed files with 17 additions and 8 deletions
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25
kernel/sched_autogroup.c
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@ -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);