Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758160AbaFYSbw (ORCPT ); Wed, 25 Jun 2014 14:31:52 -0400 Received: from mail-ob0-f175.google.com ([209.85.214.175]:61332 "EHLO mail-ob0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757536AbaFYSbt (ORCPT ); Wed, 25 Jun 2014 14:31:49 -0400 MIME-Version: 1.0 In-Reply-To: <20140625182012.GA19437@redhat.com> References: <1403642893-23107-1-git-send-email-keescook@chromium.org> <1403642893-23107-10-git-send-email-keescook@chromium.org> <20140625142121.GD7892@redhat.com> <20140625165209.GA14720@redhat.com> <20140625172410.GA17133@redhat.com> <20140625182012.GA19437@redhat.com> Date: Wed, 25 Jun 2014 11:31:48 -0700 X-Google-Sender-Auth: aGErAidmIooTIFiXMdWJrG37Qhc Message-ID: Subject: Re: [PATCH v8 9/9] seccomp: implement SECCOMP_FILTER_FLAG_TSYNC From: Kees Cook To: Oleg Nesterov Cc: linux-arch , linux-mips@linux-mips.org, Will Drewry , linux-security-module , Linux API , "x86@kernel.org" , LKML , Andy Lutomirski , Daniel Borkmann , Julien Tinnes , "Michael Kerrisk (man-pages)" , Andrew Morton , David Drysdale , "linux-arm-kernel@lists.infradead.org" , Alexei Starovoitov 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 Wed, Jun 25, 2014 at 11:20 AM, Oleg Nesterov wrote: > On 06/25, Kees Cook wrote: >> >> On Wed, Jun 25, 2014 at 10:24 AM, Oleg Nesterov wrote: >> > >> > However, do_execve() takes cred_guard_mutex at the start in prepare_bprm_creds() >> > and drops it in install_exec_creds(), so it should solve the problem? >> >> I can't tell yet. I'm still trying to understand the order of >> operations here. It looks like de_thread() takes the sighand lock. >> do_execve_common does: >> >> prepare_bprm_creds (takes cred_guard_mutex) >> check_unsafe_exec (checks nnp to set LSM_UNSAFE_NO_NEW_PRIVS) >> prepare_binprm (handles suid escalation, checks nnp separately) >> security_bprm_set_creds (checks LSM_UNSAFE_NO_NEW_PRIVS) >> exec_binprm >> load_elf_binary >> flush_old_exec >> de_thread (takes and releases sighand->lock) >> install_exec_creds (releases cred_guard_mutex) > > Yes, and note that when cred_guard_mutex is dropped all other threads > are already killed, > >> I don't see a way to use cred_guard_mutex during tsync (which holds >> sighand->lock) without dead-locking. What were you considering here? > > Just take/drop current->signal->cred_guard_mutex along with ->siglock > in seccomp_set_mode_filter() ? Unconditionally on depending on > SECCOMP_FILTER_FLAG_TSYNC. Yeah, this looks good. *whew* Testing it now, so far so good. Thanks! -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/