Re: [PATCH] audit: Only use the syscall slowpath when syscall audit rules exist
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.