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=-7.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=no 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 4621AC433E0 for ; Wed, 12 Aug 2020 01:36:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1D76D20678 for ; Wed, 12 Aug 2020 01:36:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597196189; bh=+4U+6jTRijWc8yfXbUKhh5RLnN+SeVLZft/C5Ak2Q64=; h=Date:From:To:Subject:In-Reply-To:Reply-To:List-ID:From; b=QO0iMcUSvWU7N4+Ayxd2N1Sgf/Db6TzH4Fho5HaY4fzkaaKXi1o2ePoqkdaT67uXg MsG56SyVxMayUrZrEzJ5u6HvPLyeBDdOvAloeZ4RImLvJmvR+eQfM+QJ0IDDpYLhb+ cRlRf5EoUzrYESxKRzlLAtRhlhkLCSM8vuphVT4g= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726489AbgHLBg2 (ORCPT ); Tue, 11 Aug 2020 21:36:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:37826 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726143AbgHLBg2 (ORCPT ); Tue, 11 Aug 2020 21:36:28 -0400 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 3D97E2054F; Wed, 12 Aug 2020 01:36:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597196187; bh=+4U+6jTRijWc8yfXbUKhh5RLnN+SeVLZft/C5Ak2Q64=; h=Date:From:To:Subject:In-Reply-To:From; b=xQElzeuDOJAn4ZWyAWCzKyjqPMlq7bcuhsx+QwkhasNZ/UZ3/mEm9BTd9EWNx/0bo Vzj1f3GU4eR6YKI/LYLRg5qbxOqtD0tRi5+2H/4S1kkLavyIk/zwYYduGfiIfyKNMW klGN5sjEbsnfz2gkz3d2mKrvkVxQaxgG4d957YQc= Date: Tue, 11 Aug 2020 18:36:26 -0700 From: Andrew Morton To: akpm@linux-foundation.org, christian.brauner@ubuntu.com, cyphar@cyphar.com, dvyukov@google.com, ebiggers3@gmail.com, keescook@chromium.org, linux-mm@kvack.org, mm-commits@vger.kernel.org, penguin-kernel@I-love.SAKURA.ne.jp, torvalds@linux-foundation.org, viro@zeniv.linux.org.uk Subject: [patch 117/165] exec: move S_ISREG() check earlier Message-ID: <20200812013626.i2nt1q1Cb%akpm@linux-foundation.org> In-Reply-To: <20200811182949.e12ae9a472e3b5e27e16ad6c@linux-foundation.org> User-Agent: s-nail v14.8.16 Sender: mm-commits-owner@vger.kernel.org Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Kees Cook Subject: exec: move S_ISREG() check earlier 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/ Link: http://lkml.kernel.org/r/20200605160013.3954297-3-keescook@chromium.org Signed-off-by: Kees Cook Cc: Aleksa Sarai Cc: Alexander Viro Cc: Christian Brauner Cc: Dmitry Vyukov Cc: Eric Biggers Cc: Tetsuo Handa Signed-off-by: Andrew Morton --- fs/exec.c | 14 ++++++++++++-- fs/namei.c | 6 ++++-- fs/open.c | 6 ------ 3 files changed, 16 insertions(+), 10 deletions(-) --- a/fs/exec.c~exec-move-s_isreg-check-earlier +++ a/fs/exec.c @@ -141,8 +141,13 @@ SYSCALL_DEFINE1(uselib, const char __use 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)) @@ -908,8 +913,13 @@ static struct file *do_open_execat(int f 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)) --- a/fs/namei.c~exec-move-s_isreg-check-earlier +++ a/fs/namei.c @@ -2849,16 +2849,18 @@ static int may_open(const struct path *p 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; } --- a/fs/open.c~exec-move-s_isreg-check-earlier +++ a/fs/open.c @@ -779,12 +779,6 @@ 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)) _