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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