Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753074AbaBCSdy (ORCPT ); Mon, 3 Feb 2014 13:33:54 -0500 Received: from mail-vc0-f177.google.com ([209.85.220.177]:41655 "EHLO mail-vc0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751686AbaBCSdx (ORCPT ); Mon, 3 Feb 2014 13:33:53 -0500 MIME-Version: 1.0 In-Reply-To: <20140203181144.GA29296@redhat.com> References: <20140203181144.GA29296@redhat.com> From: Andy Lutomirski Date: Mon, 3 Feb 2014 10:33:32 -0800 Message-ID: Subject: Re: [PATCH] audit: Only use the syscall slowpath when syscall audit rules exist To: Oleg Nesterov Cc: linux-audit@redhat.com, "linux-kernel@vger.kernel.org" , Andi Kleen , Steve Grubb , Eric Paris Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 3, 2014 at 10:11 AM, Oleg Nesterov wrote: > 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. I didn't notice that option :) > > And I am not sure why n_rules_lock is rwlock_t... OK, to make > audit_alloc() more scalable, I guess. Please see below. > Yes. I should probably also use the irqsave variant. >> @@ -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(). Hmm. I missed that. > > 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. Here are two options: 1. Sync the flags inside tasklist_lock, as I think you're suggesting. This seems simple. 2. Make this whole thing lazy -- always set TIF_SYSCALL_AUDIT for new tasks, but clear it on the first syscall. I'm leaning toward number 1. Thanks for the instant review! --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/