From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.0 required=3.0 tests=BAD_ENC_HEADER,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BEBA5C433E3 for ; Tue, 11 Aug 2020 19:40:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9603D20774 for ; Tue, 11 Aug 2020 19:40:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726329AbgHKTkT convert rfc822-to-8bit (ORCPT ); Tue, 11 Aug 2020 15:40:19 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:58502 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726068AbgHKTkS (ORCPT ); Tue, 11 Aug 2020 15:40:18 -0400 Received: from in01.mta.xmission.com ([166.70.13.51]) by out01.mta.xmission.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.93) (envelope-from ) id 1k5a7y-009jin-2l; Tue, 11 Aug 2020 13:40:06 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1k5a7w-0004Qr-Ti; Tue, 11 Aug 2020 13:40:05 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= Cc: linux-kernel@vger.kernel.org, Aleksa Sarai , Alexei Starovoitov , Al Viro , Andrew Morton , Andy Lutomirski , Christian Brauner , Christian Heimes , Daniel Borkmann , Deven Bowers , Dmitry Vyukov , Eric Biggers , Eric Chiang , Florian Weimer , James Morris , Jan Kara , Jann Horn , Jonathan Corbet , Kees Cook , Lakshmi Ramasubramanian , Matthew Garrett , Matthew Wilcox , Michael Kerrisk , Mimi Zohar , Philippe =?utf-8?Q?Tr=C3=A9buchet?= , Scott Shell , Sean Christopherson , Shuah Khan , Steve Dower , Steve Grubb , Tetsuo Handa , Thibaut Sautereau , Vincent Strubel , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org References: <20200723171227.446711-1-mic@digikod.net> <20200723171227.446711-4-mic@digikod.net> Date: Tue, 11 Aug 2020 14:36:38 -0500 In-Reply-To: <20200723171227.446711-4-mic@digikod.net> (=?utf-8?Q?=22Micka?= =?utf-8?Q?=C3=ABl_Sala=C3=BCn=22's?= message of "Thu, 23 Jul 2020 19:12:23 +0200") Message-ID: <87a6z1m0u1.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-XM-SPF: eid=1k5a7w-0004Qr-Ti;;;mid=<87a6z1m0u1.fsf@x220.int.ebiederm.org>;;;hst=in01.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX18bRw6Qx631bJvZB6GAyvN2Z5/PhB9504A= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH v7 3/7] exec: Move path_noexec() check earlier X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org Mickaël Salaün writes: > From: Kees Cook > > The path_noexec() check, like the regular file check, was happening too > late, letting LSMs see impossible execve()s. Check it earlier as well > in may_open() and collect the redundant fs/exec.c path_noexec() test > under the same robustness comment as the S_ISREG() check. > > My notes on the call path, and related arguments, checks, etc: A big question arises, that I think someone already asked. Why perform this test in may_open directly instead of moving it into inode_permission. That way the code can be shared with faccessat, and any other code path that wants it? That would look to provide a more maintainable kernel. Eric > do_open_execat() > struct open_flags open_exec_flags = { > .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC, > .acc_mode = MAY_EXEC, > ... > do_filp_open(dfd, filename, open_flags) > path_openat(nameidata, open_flags, flags) > file = alloc_empty_file(open_flags, current_cred()); > do_open(nameidata, file, open_flags) > may_open(path, acc_mode, open_flag) > /* new location of MAY_EXEC vs path_noexec() test */ > inode_permission(inode, MAY_OPEN | acc_mode) > security_inode_permission(inode, acc_mode) > vfs_open(path, file) > do_dentry_open(file, path->dentry->d_inode, open) > security_file_open(f) > open() > /* old location of path_noexec() test */ > > Signed-off-by: Mickaël Salaün > Signed-off-by: Kees Cook > Link: https://lore.kernel.org/r/20200605160013.3954297-4-keescook@chromium.org > --- > fs/exec.c | 12 ++++-------- > fs/namei.c | 4 ++++ > 2 files changed, 8 insertions(+), 8 deletions(-) > > diff --git a/fs/exec.c b/fs/exec.c > index bdc6a6eb5dce..4eea20c27b01 100644 > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -147,10 +147,8 @@ SYSCALL_DEFINE1(uselib, const char __user *, library) > * and check again at the very end too. > */ > error = -EACCES; > - if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode))) > - goto exit; > - > - if (path_noexec(&file->f_path)) > + if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) || > + path_noexec(&file->f_path))) > goto exit; > > fsnotify_open(file); > @@ -897,10 +895,8 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags) > * and check again at the very end too. > */ > err = -EACCES; > - if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode))) > - goto exit; > - > - if (path_noexec(&file->f_path)) > + if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) || > + path_noexec(&file->f_path))) > goto exit; > > err = deny_write_access(file); > diff --git a/fs/namei.c b/fs/namei.c > index a559ad943970..ddc9b25540fe 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -2863,6 +2863,10 @@ static int may_open(const struct path *path, int acc_mode, int flag) > return -EACCES; > flag &= ~O_TRUNC; > break; > + case S_IFREG: > + if ((acc_mode & MAY_EXEC) && path_noexec(path)) > + return -EACCES; > + break; > } > > error = inode_permission(inode, MAY_OPEN | acc_mode);