Messages in this thread Patch in this message | | | Date | Sat, 30 Jun 2012 07:24:53 +0100 | From | Al Viro <> | Subject | Re: [PATCH 0/4] Was: deferring __fput() |
| |
On Thu, Jun 28, 2012 at 06:45:39PM +0200, Oleg Nesterov wrote: > Forgot to mention... > > And I still think that task_work_add() should not succeed unconditionally, > it synchronize with exit_task_work(). Otherwise keyctl_session_to_parent() > is broken.
Hmm... Look: if nothing else, we have /* the parent mustn't be init and mustn't be a kernel thread */ if (parent->pid <= 1 || !parent->mm) goto unlock; in the caller. OTOH, on the exit side we have exit_mm() done first. And that will have ->mm set to NULL. So we are closing a very narrow race to start with. So why not do the following and be done with that?
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c index 0291b3f..f1b59ae 100644 --- a/security/keys/keyctl.c +++ b/security/keys/keyctl.c @@ -1486,6 +1486,7 @@ long keyctl_session_to_parent(void) oldwork = NULL; parent = me->real_parent; + task_lock(parent); /* the parent mustn't be init and mustn't be a kernel thread */ if (parent->pid <= 1 || !parent->mm) goto unlock; @@ -1529,6 +1530,7 @@ long keyctl_session_to_parent(void) if (!ret) newwork = NULL; unlock: + task_unlock(parent); write_unlock_irq(&tasklist_lock); rcu_read_unlock(); if (oldwork)
| |