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>
diff --git a/kernel/sched_autogroup.c b/kernel/sched_autogroup.c
index 57a7ac28..c80fedc 100644
--- a/kernel/sched_autogroup.c
+++ b/kernel/sched_autogroup.c
@@ -41,6 +41,20 @@
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 @@
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 @@
#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 @@
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 @@
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);