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=-13.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 F3080C43446 for ; Tue, 14 Jul 2020 18:17:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DCF5922838 for ; Tue, 14 Jul 2020 18:17:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729191AbgGNSRG (ORCPT ); Tue, 14 Jul 2020 14:17:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33726 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729218AbgGNSQ7 (ORCPT ); Tue, 14 Jul 2020 14:16:59 -0400 Received: from smtp-190b.mail.infomaniak.ch (smtp-190b.mail.infomaniak.ch [IPv6:2001:1600:3:17::190b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 443D7C08C5DD for ; Tue, 14 Jul 2020 11:16:59 -0700 (PDT) Received: from smtp-3-0001.mail.infomaniak.ch (unknown [10.4.36.108]) by smtp-2-3000.mail.infomaniak.ch (Postfix) with ESMTPS id 4B5pcz4h40zlhGky; Tue, 14 Jul 2020 20:16:51 +0200 (CEST) Received: from localhost (unknown [94.23.54.103]) by smtp-3-0001.mail.infomaniak.ch (Postfix) with ESMTPA id 4B5pcz1YDGzlh8TC; Tue, 14 Jul 2020 20:16:51 +0200 (CEST) From: =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= To: linux-kernel@vger.kernel.org Cc: =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= , 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 , =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= , Mimi Zohar , =?UTF-8?q?Philippe=20Tr=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 Subject: [PATCH v6 2/7] exec: Move S_ISREG() check earlier Date: Tue, 14 Jul 2020 20:16:33 +0200 Message-Id: <20200714181638.45751-3-mic@digikod.net> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20200714181638.45751-1-mic@digikod.net> References: <20200714181638.45751-1-mic@digikod.net> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 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-api-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org From: Kees Cook The execve(2)/uselib(2) syscalls have always rejected non-regular files. Recently, it was noticed that a deadlock was introduced when trying to execute pipes, as the S_ISREG() test was happening too late. This was fixed in commit 73601ea5b7b1 ("fs/open.c: allow opening only regular files during execve()"), but it was added after inode_permission() had already run, which meant LSMs could see bogus attempts to execute non-regular files. Move the test into the other inode type checks (which already look for other pathological conditions[1]). Since there is no need to use FMODE_EXEC while we still have access to "acc_mode", also switch the test to MAY_EXEC. Also include a comment with the redundant S_ISREG() checks at the end of execve(2)/uselib(2) to note that they are present to avoid any mistakes. My notes on the call path, and related arguments, checks, etc: 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 S_ISREG() 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) /* old location of FMODE_EXEC vs S_ISREG() test */ security_file_open(f) open() [1] https://lore.kernel.org/lkml/202006041910.9EF0C602@keescook/ Signed-off-by: Kees Cook Acked-by: Mickaël Salaün Link: https://lore.kernel.org/r/20200605160013.3954297-3-keescook@chromium.org --- fs/exec.c | 14 ++++++++++++-- fs/namei.c | 6 ++++-- fs/open.c | 6 ------ 3 files changed, 16 insertions(+), 10 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index d7c937044d10..bdc6a6eb5dce 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -141,8 +141,13 @@ SYSCALL_DEFINE1(uselib, const char __user *, library) if (IS_ERR(file)) goto out; + /* + * may_open() has already checked for this, so it should be + * impossible to trip now. But we need to be extra cautious + * and check again at the very end too. + */ error = -EACCES; - if (!S_ISREG(file_inode(file)->i_mode)) + if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode))) goto exit; if (path_noexec(&file->f_path)) @@ -886,8 +891,13 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags) if (IS_ERR(file)) goto out; + /* + * may_open() has already checked for this, so it should be + * impossible to trip now. But we need to be extra cautious + * and check again at the very end too. + */ err = -EACCES; - if (!S_ISREG(file_inode(file)->i_mode)) + if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode))) goto exit; if (path_noexec(&file->f_path)) diff --git a/fs/namei.c b/fs/namei.c index 72d4219c93ac..a559ad943970 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -2849,16 +2849,18 @@ static int may_open(const struct path *path, int acc_mode, int flag) case S_IFLNK: return -ELOOP; case S_IFDIR: - if (acc_mode & MAY_WRITE) + if (acc_mode & (MAY_WRITE | MAY_EXEC)) return -EISDIR; break; case S_IFBLK: case S_IFCHR: if (!may_open_dev(path)) return -EACCES; - /*FALLTHRU*/ + fallthrough; case S_IFIFO: case S_IFSOCK: + if (acc_mode & MAY_EXEC) + return -EACCES; flag &= ~O_TRUNC; break; } diff --git a/fs/open.c b/fs/open.c index 6cd48a61cda3..623b7506a6db 100644 --- a/fs/open.c +++ b/fs/open.c @@ -784,12 +784,6 @@ static int do_dentry_open(struct file *f, return 0; } - /* Any file opened for execve()/uselib() has to be a regular file. */ - if (unlikely(f->f_flags & FMODE_EXEC && !S_ISREG(inode->i_mode))) { - error = -EACCES; - goto cleanup_file; - } - if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) { error = get_write_access(inode); if (unlikely(error)) -- 2.27.0