Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753106AbaBCSL5 (ORCPT ); Mon, 3 Feb 2014 13:11:57 -0500 Received: from mx1.redhat.com ([209.132.183.28]:35749 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752350AbaBCSL4 (ORCPT ); Mon, 3 Feb 2014 13:11:56 -0500 Date: Mon, 3 Feb 2014 19:11:44 +0100 From: Oleg Nesterov To: Andy Lutomirski Cc: linux-audit@redhat.com, linux-kernel@vger.kernel.org, Andi Kleen , Steve Grubb , Eric Paris Subject: Re: [PATCH] audit: Only use the syscall slowpath when syscall audit rules exist Message-ID: <20140203181144.GA29296@redhat.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. -- 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/