Messages in this thread | | | Date | Mon, 10 Feb 2014 17:57:23 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH v3] audit: Turn off TIF_SYSCALL_AUDIT when there are no rules |
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On 02/08, Andy Lutomirski wrote: > > +void audit_inc_n_rules() > +{ > + struct task_struct *p, *t; > + > + read_lock(&tasklist_lock); > + audit_n_rules++; > + smp_wmb(); > + if (audit_n_rules == 1) { > + /* > + * We now have a rule; we need to hook syscall entry. > + */ > + for_each_process_thread(p, t) { > + if (t->audit_context) > + set_tsk_thread_flag(t, TIF_SYSCALL_AUDIT); > + } > + } > + read_unlock(&tasklist_lock); > +} > + > +void audit_dec_n_rules() > +{ > + read_lock(&tasklist_lock); > + --audit_n_rules; > + BUG_ON(audit_n_rules < 0); > + > + /* > + * If audit_n_rules == 0, then __audit_syscall_exit will clear > + * TIF_SYSCALL_AUDIT. > + */ > + > + read_unlock(&tasklist_lock); > +}
To be honest, I do not understand why _dec_ takes tasklist_lock... And why _inc_ increments audit_n_rules under tasklist.
> @@ -1528,6 +1562,25 @@ void __audit_syscall_exit(int success, long return_code) > context->filterkey = NULL; > } > tsk->audit_context = context; > + > + if (ACCESS_ONCE(audit_n_rules) == 0) { > + /* > + * Either this is the very first syscall by this process or > + * audit_dec_n_rules recently set audit_n_rules to zero. > + */ > + smp_rmb();
rmb() looks wrong, we need mb() to serialize ACCESS_ONCE() and clear_tsk_thread_flag().
But, otoh, I think we do not need any barrier at all, we can rely on control dependency. See the recent 18c03c61444a21 "Documentation/ memory-barriers.txt: Prohibit speculative writes".
> + /* audit_inc_n_rules could increment audit_n_rules here... */ > + > + clear_tsk_thread_flag(tsk, TIF_SYSCALL_AUDIT); > + > + smp_rmb();
Again, I guess this should be mb() or smp_mb__after_clear_bit().
And I still think this needs more changes. Once again, I do not think that, say, __audit_log_bprm_fcaps() should populate context->aux if !TIF_SYSCALL_AUDIT, this list can grow indefinitely. Or __audit_signal_info()...
Perhaps __audit_syscall_exit() should also set context->dummy?
Oleg.
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