Messages in this thread | | | Date | Mon, 3 Feb 2014 19:11:44 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH] audit: Only use the syscall slowpath when syscall audit rules exist |
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On 02/03, Andy Lutomirski wrote: > > @@ -911,6 +918,47 @@ static inline struct audit_context *audit_alloc_context(enum audit_state state) > return context; > } > > +void audit_inc_n_rules() > +{ > + struct task_struct *p, *g; > + > + write_lock(&n_rules_lock); > + > + if (audit_n_rules++ != 0) > + goto out; /* The overall state isn't changing. */ > + > + read_lock(&tasklist_lock); > + do_each_thread(g, p) { > + if (p->audit_context) > + set_tsk_thread_flag(p, TIF_SYSCALL_AUDIT); > + } while_each_thread(g, p); > + read_unlock(&tasklist_lock);
Cosmetic, but I'd suggest to use for_each_process_thread() instead of do_each_thread/while_each_thread.
And I am not sure why n_rules_lock is rwlock_t... OK, to make audit_alloc() more scalable, I guess. Please see below.
> @@ -942,8 +995,14 @@ int audit_alloc(struct task_struct *tsk) > } > context->filterkey = key; > > + read_lock(&n_rules_lock); > tsk->audit_context = context; > - set_tsk_thread_flag(tsk, TIF_SYSCALL_AUDIT); > + if (audit_n_rules) > + set_tsk_thread_flag(tsk, TIF_SYSCALL_AUDIT); > + else > + clear_tsk_thread_flag(tsk, TIF_SYSCALL_AUDIT); > + read_unlock(&n_rules_lock);
Perhaps this is fine, but n_rules_lock can't prevent the race with audit_inc/dec_n_rules(). The problem is, this is called before the new task is visible to for_each_process_thread().
If we want to fix this race, we need something like audit_sync_flags() called after copy_process() drops tasklist, or from tasklist_lock protected section (in this case it doesn't need n_rules_lock).
Or perhaps audit_alloc() should not try to clear TIF_SYSCALL_AUDIT at all. In both cases n_rules_lock can be spinlock_t.
Oleg.
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