Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754053AbaFXSTb (ORCPT ); Tue, 24 Jun 2014 14:19:31 -0400 Received: from mail-ob0-f177.google.com ([209.85.214.177]:40677 "EHLO mail-ob0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753578AbaFXST1 (ORCPT ); Tue, 24 Jun 2014 14:19:27 -0400 MIME-Version: 1.0 In-Reply-To: <20140624170800.GA30480@redhat.com> References: <1403560693-21809-1-git-send-email-keescook@chromium.org> <1403560693-21809-8-git-send-email-keescook@chromium.org> <20140624170800.GA30480@redhat.com> Date: Tue, 24 Jun 2014 11:19:27 -0700 X-Google-Sender-Auth: Vx3w-_bw-Aw9mDTILTb1K-gSch8 Message-ID: Subject: Re: [PATCH v7 7/9] seccomp: implement SECCOMP_FILTER_FLAG_TSYNC From: Kees Cook To: Oleg Nesterov Cc: LKML , Andy Lutomirski , Alexei Starovoitov , "Michael Kerrisk (man-pages)" , Andrew Morton , Daniel Borkmann , Will Drewry , Julien Tinnes , David Drysdale , Linux API , "x86@kernel.org" , "linux-arm-kernel@lists.infradead.org" , linux-mips@linux-mips.org, linux-arch , linux-security-module Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 24, 2014 at 10:08 AM, Oleg Nesterov wrote: > On 06/23, Kees Cook wrote: >> >> +static pid_t seccomp_can_sync_threads(void) >> +{ >> + struct task_struct *thread, *caller; >> + >> + BUG_ON(write_can_lock(&tasklist_lock)); >> + BUG_ON(!spin_is_locked(¤t->sighand->siglock)); >> + >> + if (current->seccomp.mode != SECCOMP_MODE_FILTER) >> + return -EACCES; >> + >> + /* Validate all threads being eligible for synchronization. */ >> + thread = caller = current; >> + for_each_thread(caller, thread) { > > You only need to initialize "caller" for for_each_thread(). Same for > seccomp_sync_threads(). Thanks, I'll fix this up. >> @@ -586,6 +701,17 @@ static long seccomp_set_mode_filter(unsigned int flags, >> if (IS_ERR(prepared)) >> return PTR_ERR(prepared); >> >> + /* >> + * If we're doing thread sync, we must hold tasklist_lock >> + * to make sure seccomp filter changes are stable on threads >> + * entering or leaving the task list. And we must take it >> + * before the sighand lock to avoid deadlocking. >> + */ >> + if (flags & SECCOMP_FILTER_FLAG_TSYNC) >> + write_lock_irqsave(&tasklist_lock, taskflags); >> + else >> + __acquire(&tasklist_lock); /* keep sparse happy */ >> + > > Why? ->siglock should be enough, it seems. > > It obviously does not protect the global process list, but *sync_threads() > only care about current's thread group list, no? I think I was concerned about the exit case, but reading through those paths again, I can't find a race. Calls to put_seccomp_filter() should already be safe. Let me see what happens if I drop the tasklist_lock usage... -Kees -- Kees Cook Chrome OS Security -- 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/