From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oleg Nesterov Subject: Re: [PATCH v8 9/9] seccomp: implement SECCOMP_FILTER_FLAG_TSYNC Date: Wed, 25 Jun 2014 20:20:12 +0200 Message-ID: <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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-subscribe: List-owner: List-post: List-archive: To: Kees Cook Cc: LKML , Andy Lutomirski , "Michael Kerrisk (man-pages)" , Alexei Starovoitov , 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 List-Id: linux-arch.vger.kernel.org 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. Oleg. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:19637 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756153AbaFYSVy (ORCPT ); Wed, 25 Jun 2014 14:21:54 -0400 Date: Wed, 25 Jun 2014 20:20:12 +0200 From: Oleg Nesterov Subject: Re: [PATCH v8 9/9] seccomp: implement SECCOMP_FILTER_FLAG_TSYNC Message-ID: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Kees Cook Cc: LKML , Andy Lutomirski , "Michael Kerrisk (man-pages)" , Alexei Starovoitov , 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 Message-ID: <20140625182012.rIziDLsE_KXXvXFgUPwjFziquaIbjsEPThgdsCnZC6M@z> 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. Oleg.