Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752280AbaFXTIW (ORCPT ); Tue, 24 Jun 2014 15:08:22 -0400 Received: from mail-ob0-f180.google.com ([209.85.214.180]:48326 "EHLO mail-ob0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750974AbaFXTIR (ORCPT ); Tue, 24 Jun 2014 15:08:17 -0400 MIME-Version: 1.0 In-Reply-To: <20140624183749.GC1258@redhat.com> References: <1403560693-21809-1-git-send-email-keescook@chromium.org> <1403560693-21809-8-git-send-email-keescook@chromium.org> <20140624172753.GA31435@redhat.com> <20140624183749.GC1258@redhat.com> Date: Tue, 24 Jun 2014 12:08:16 -0700 X-Google-Sender-Auth: jtcyTBS-8hLg3tdrJqFc-3Cbong 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 11:37 AM, Oleg Nesterov wrote: > On 06/24, Kees Cook wrote: >> >> On Tue, Jun 24, 2014 at 10:27 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) { >> >> + pid_t failed; >> >> + >> >> + if (thread->seccomp.mode == SECCOMP_MODE_DISABLED || >> >> + (thread->seccomp.mode == SECCOMP_MODE_FILTER && >> >> + is_ancestor(thread->seccomp.filter, >> >> + caller->seccomp.filter))) >> >> + continue; >> >> + >> >> + /* Return the first thread that cannot be synchronized. */ >> >> + failed = task_pid_vnr(thread); >> >> + /* If the pid cannot be resolved, then return -ESRCH */ >> >> + if (failed == 0) >> >> + failed = -ESRCH; >> > >> > forgot to mention, task_pid_vnr() can't fail. sighand->siglock is held, >> > for_each_thread() can't see a thread which has passed unhash_process(). >> >> Certainly good to know, but I'd be much more comfortable leaving this >> check as-is. Having "failed" return with "0" would be very very bad >> (userspace would think the filter had been successfully applied, etc). >> I'd rather stay highly defensive here. > > OK, agreed. Although in this case I'd suggest > > if (WARN_ON(failed == 0)) > failed = -ESRCH; > > but I won't insist. Excellent idea, yes! I'll include this as well. -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/