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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B1CEBC433EF for ; Tue, 1 Mar 2022 09:22:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233714AbiCAJX1 (ORCPT ); Tue, 1 Mar 2022 04:23:27 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44624 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232384AbiCAJXX (ORCPT ); Tue, 1 Mar 2022 04:23:23 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7DF47AE7B; Tue, 1 Mar 2022 01:22:42 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 15785B81855; Tue, 1 Mar 2022 09:22:41 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B0972C340EE; Tue, 1 Mar 2022 09:22:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1646126559; bh=ZpG11DD4kp9h4/beH993WEeMr4LguyKwWCvtJOaP/8Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=AnDeyLB9EgfvQl+AhT8DrwEAFMRcAPKHtHDA+fV+HVqwv7K95N7zFGRi+C02gLXXw s5r1eCRjv7MhkHR4z/ahqeB4jJXrLfkNGguy50QZ/En2FgqadneXBA/W5x/T5mJGUK gqzit1E5G3zEbf4tWBZE6EuDHtjxx4Bqvr8hMJLK4eTzgfIPTERMFMriwGyEHBL4hM kA0sp8o7K59oEvKW5QRUZoDcuIpYLoKYoNwfP7S8LvVV3vaxjZ9JZX05FD4O8oeJ5U oMQUkxOfqnivmB4BXGvg8TLkEcLrCa9882/+SJGvQewS9fD6KBH/lWHDiRbD1BqHN2 nb4eVLfQxbbEQ== Date: Tue, 1 Mar 2022 10:22:32 +0100 From: Christian Brauner To: =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= Cc: Al Viro , Casey Schaufler , "Darrick J . Wong" , Eric Paris , James Morris , John Johansen , Kentaro Takeda , Miklos Szeredi , Paul Moore , "Serge E . Hallyn" , Stephen Smalley , Steve French , Tetsuo Handa , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= Subject: Re: [PATCH v1] fs: Fix inconsistent f_mode Message-ID: <20220301092232.wh7m3fxbe7hyxmcu@wittgenstein> References: <20220228215935.748017-1-mic@digikod.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220228215935.748017-1-mic@digikod.net> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 28, 2022 at 10:59:35PM +0100, Mickaël Salaün wrote: > From: Mickaël Salaün > > While transitionning to ACC_MODE() with commit 5300990c0370 ("Sanitize > f_flags helpers") and then fixing it with commit 6d125529c6cb ("Fix > ACC_MODE() for real"), we lost an open flags consistency check. Opening > a file with O_WRONLY | O_RDWR leads to an f_flags containing MAY_READ | > MAY_WRITE (thanks to the ACC_MODE() helper) and an empty f_mode. > Indeed, the OPEN_FMODE() helper transforms 3 (an incorrect value) to 0. > > Fortunately, vfs_read() and vfs_write() both check for FMODE_READ, or > respectively FMODE_WRITE, and return an EBADF error if it is absent. > Before commit 5300990c0370 ("Sanitize f_flags helpers"), opening a file > with O_WRONLY | O_RDWR returned an EINVAL error. Let's restore this safe > behavior. That specific part seems a bit risky at first glance. Given that the patch referenced is from 2009 this means we've been allowing O_WRONLY | O_RDWR to succeed for almost 13 years now. > > To make it consistent with ACC_MODE(), this patch also changes > OPEN_FMODE() to return FMODE_READ | FMODE_WRITE for O_WRONLY | O_RDWR. > This may help protect from potential spurious issues. > > This issue could result in inconsistencies with AppArmor, Landlock and > SELinux, but the VFS checks would still forbid read and write accesses. > Tomoyo uses the ACC_MODE() transformation which is correct, and Smack > doesn't check the file mode. Filesystems using OPEN_FMODE() should also > be protected by the VFS checks. > > Fixes: 5300990c0370 ("Sanitize f_flags helpers") > Cc: Al Viro > Cc: Casey Schaufler > Cc: Darrick J. Wong > Cc: Eric Paris > Cc: John Johansen > Cc: Kentaro Takeda > Cc: Miklos Szeredi > Cc: Paul Moore > Cc: Stephen Smalley > Cc: Steve French > Cc: Tetsuo Handa > Signed-off-by: Mickaël Salaün > Link: https://lore.kernel.org/r/20220228215935.748017-1-mic@digikod.net > --- > fs/file_table.c | 3 +++ > include/linux/fs.h | 5 +++-- > 2 files changed, 6 insertions(+), 2 deletions(-) > > diff --git a/fs/file_table.c b/fs/file_table.c > index 7d2e692b66a9..b936f69525d0 100644 > --- a/fs/file_table.c > +++ b/fs/file_table.c > @@ -135,6 +135,9 @@ static struct file *__alloc_file(int flags, const struct cred *cred) > struct file *f; > int error; > > + if ((flags & O_ACCMODE) == O_ACCMODE) > + return ERR_PTR(-EINVAL); > + > f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL); > if (unlikely(!f)) > return ERR_PTR(-ENOMEM); > diff --git a/include/linux/fs.h b/include/linux/fs.h > index e2d892b201b0..83bc5aaf1c41 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -3527,8 +3527,9 @@ int __init list_bdev_fs_names(char *buf, size_t size); > #define __FMODE_NONOTIFY ((__force int) FMODE_NONOTIFY) > > #define ACC_MODE(x) ("\004\002\006\006"[(x)&O_ACCMODE]) > -#define OPEN_FMODE(flag) ((__force fmode_t)(((flag + 1) & O_ACCMODE) | \ > - (flag & __FMODE_NONOTIFY))) > +#define OPEN_FMODE(flag) ((__force fmode_t)( \ > + (((flag + 1) & O_ACCMODE) ?: O_ACCMODE) | \ > + (flag & __FMODE_NONOTIFY))) > > static inline bool is_sxid(umode_t mode) > { > > base-commit: 7e57714cd0ad2d5bb90e50b5096a0e671dec1ef3 > -- > 2.35.1 >