the patch below fixes a bug that i encountered while running a
PREEMPT_RT kernel, but i believe it should be fixed in the generic
kernel too. xfrm_policy_kill() queues a destroyed policy structure to
the GC list, and unlocks the policy->lock spinlock _after_ that point.
This created a scenario where GC processing got to the new structure
first, and kfree()d it - then the write_unlock_bh() was done on the
already kfreed structure. There is no guarantee that GC processing will
be done after policy->lock has been dropped and softirq processing has
been enabled.
Signed-off-by: Ingo Molnar <[email protected]>
--- linux/net/xfrm/xfrm_policy.c.orig
+++ linux/net/xfrm/xfrm_policy.c
@@ -301,18 +301,22 @@ static void xfrm_policy_gc_task(void *da
static void xfrm_policy_kill(struct xfrm_policy *policy)
{
write_lock_bh(&policy->lock);
- if (policy->dead)
- goto out;
-
+ if (policy->dead) {
+ write_unlock_bh(&policy->lock);
+ return;
+ }
policy->dead = 1;
spin_lock(&xfrm_policy_gc_lock);
list_add(&policy->list, &xfrm_policy_gc_list);
+ /*
+ * Unlock the policy (out of order unlocking), to make sure
+ * the GC context does not free it with an active lock:
+ */
+ write_unlock_bh(&policy->lock);
spin_unlock(&xfrm_policy_gc_lock);
- schedule_work(&xfrm_policy_gc_work);
-out:
- write_unlock_bh(&policy->lock);
+ schedule_work(&xfrm_policy_gc_work);
}
/* Generate new index... KAME seems to generate them ordered by cost
-
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