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=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=ham 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 2E80CC433E1 for ; Thu, 13 Aug 2020 15:31:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 15D9B20781 for ; Thu, 13 Aug 2020 15:31:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726606AbgHMPb3 (ORCPT ); Thu, 13 Aug 2020 11:31:29 -0400 Received: from smtp-42ac.mail.infomaniak.ch ([84.16.66.172]:59295 "EHLO smtp-42ac.mail.infomaniak.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726131AbgHMPb2 (ORCPT ); Thu, 13 Aug 2020 11:31:28 -0400 Received: from smtp-3-0001.mail.infomaniak.ch (unknown [10.4.36.108]) by smtp-3-3000.mail.infomaniak.ch (Postfix) with ESMTPS id 4BS9XG4mmCzlhLv2; Thu, 13 Aug 2020 17:31:26 +0200 (CEST) Received: from ns3096276.ip-94-23-54.eu (unknown [94.23.54.103]) by smtp-3-0001.mail.infomaniak.ch (Postfix) with ESMTPA id 4BS9XC0vpZzlh8T5; Thu, 13 Aug 2020 17:31:23 +0200 (CEST) Subject: Re: [PATCH v7 3/7] exec: Move path_noexec() check earlier To: "Eric W. Biederman" , Kees Cook 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 , Lakshmi Ramasubramanian , Matthew Garrett , Matthew Wilcox , Michael Kerrisk , Mimi Zohar , =?UTF-8?Q?Philippe_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> <87a6z1m0u1.fsf@x220.int.ebiederm.org> From: =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= Message-ID: <89b6bb7f-d841-cf0a-8d5c-26c611b56ae7@digikod.net> Date: Thu, 13 Aug 2020 17:31:22 +0200 User-Agent: MIME-Version: 1.0 In-Reply-To: <87a6z1m0u1.fsf@x220.int.ebiederm.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Antivirus: Dr.Web (R) for Unix mail servers drweb plugin ver.6.0.2.8 X-Antivirus-Code: 0x100000 Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org Kees Cook wrote this patch, which is in Andrew Morton's tree, but I think you're talking about O_MAYEXEC, not this patch specifically. On 11/08/2020 21:36, Eric W. Biederman wrote: > 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. Al Viro and Jann Horn expressed such concerns for O_MAYEXEC: https://lore.kernel.org/lkml/0cc94c91-afd3-27cd-b831-8ea16ca8ca93@digikod.net/ > > 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? This patch is just a refactoring. About O_MAYEXEC, path-based LSM, IMA and IPE need to work on a struct file, whereas inode_permission() only gives a struct inode. However, faccessat2(2) (with extended flags) seems to be the perfect candidate if we want to be able to check file descriptors. > > That would look to provide a more maintainable kernel. Why would it be more maintainable? > > 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);