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 2BE0EC25B06 for ; Thu, 11 Aug 2022 17:15:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235351AbiHKRP0 (ORCPT ); Thu, 11 Aug 2022 13:15:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44730 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235108AbiHKROr (ORCPT ); Thu, 11 Aug 2022 13:14:47 -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 CAAD3EA6 for ; Thu, 11 Aug 2022 09:59:31 -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 4M3Y1t1RrqzMqNP5; Thu, 11 Aug 2022 18:59:30 +0200 (CEST) Received: from ns3096276.ip-94-23-54.eu (unknown [23.97.221.149]) by smtp-3-0001.mail.infomaniak.ch (Postfix) with ESMTPA id 4M3Y1s2yH3zln8Vd; Thu, 11 Aug 2022 18:59:29 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=digikod.net; s=20191114; t=1660237170; bh=LSlcy2SLvMkGTKXYuNvaBfeuyw7ATcD4CeV8gpzoDQ0=; h=Date:To:Cc:References:From:Subject:In-Reply-To:From; b=dEUQJhS26w7CbWzHz6pue1x3aAcbSQfmsqisr8ntWmKizc8G4ZzHeL0gV3BoQSBGn L22DQObhJQlY/8v2FGGpyunl9TlPvC0d6NX1/QUEz6ZQm2lED4+feo+JMO/VkWdPj9 ezE6U0ZR2PR7D0Uq2EE6q6xAfNtU5hScAw+vVJoM= Message-ID: Date: Thu, 11 Aug 2022 18:59:28 +0200 MIME-Version: 1.0 User-Agent: Content-Language: en-US To: =?UTF-8?Q?G=c3=bcnther_Noack?= , linux-security-module@vger.kernel.org Cc: James Morris , Paul Moore , "Serge E . Hallyn" References: <20220804193746.9161-1-gnoack3000@gmail.com> <20220804193746.9161-2-gnoack3000@gmail.com> From: =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= Subject: Re: [PATCH v3 1/4] landlock: Support file truncation In-Reply-To: <20220804193746.9161-2-gnoack3000@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: On 04/08/2022 21:37, Günther Noack wrote: > Introduce the LANDLOCK_ACCESS_FS_TRUNCATE flag for file truncation. > > This flag hooks into the path_truncate LSM hook and covers file > truncation using truncate(2), ftruncate(2), open(2) with O_TRUNC, as > well as creat(). > > This change also increments the Landlock ABI version, updates > corresponding selftests, and includes minor documentation changes to > document the flag. > > Signed-off-by: Günther Noack > --- > Documentation/userspace-api/landlock.rst | 6 ++++++ > include/uapi/linux/landlock.h | 17 ++++++++++++----- > security/landlock/fs.c | 9 ++++++++- > security/landlock/limits.h | 2 +- > security/landlock/syscalls.c | 2 +- > tools/testing/selftests/landlock/base_test.c | 2 +- > tools/testing/selftests/landlock/fs_test.c | 7 ++++--- > 7 files changed, 33 insertions(+), 12 deletions(-) > > diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst > index b8ea59493964..d92e335380d4 100644 > --- a/Documentation/userspace-api/landlock.rst > +++ b/Documentation/userspace-api/landlock.rst > @@ -380,6 +380,12 @@ by the Documentation/admin-guide/cgroup-v1/memory.rst. > Previous limitations > ==================== > > +File truncation (ABI < 3) > +------------------------- > + > +File truncation could not be denied before the third Landlock ABI, so it is > +always allowed when using a kernel that only supports the first or second ABI. I think this addition could make the documentation more consistent and helpful: Starting with the Landlock ABI version 3, it is now possible to securely control truncation thanks to the new `LANDLOCK_ACCESS_FS_TRUNCATE` access right. > + > File renaming and linking (ABI 1) > --------------------------------- > > diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h > index 23df4e0e8ace..1beb8289708d 100644 > --- a/include/uapi/linux/landlock.h > +++ b/include/uapi/linux/landlock.h > @@ -95,8 +95,15 @@ struct landlock_path_beneath_attr { > * A file can only receive these access rights: > * > * - %LANDLOCK_ACCESS_FS_EXECUTE: Execute a file. > - * - %LANDLOCK_ACCESS_FS_WRITE_FILE: Open a file with write access. > + * - %LANDLOCK_ACCESS_FS_WRITE_FILE: Open a file with write access. Note that > + * you might additionally need the LANDLOCK_ACCESS_FS_TRUNCATE right in order Please use backquotes for code such as `LANDLOCK_ACCESS_FS_TRUNCATE`, `O_TRUNC`… > + * to overwrite files with :manpage:`open(2)` using O_TRUNC or > + * :manpage:`creat(2)`. > * - %LANDLOCK_ACCESS_FS_READ_FILE: Open a file with read access. > + * - %LANDLOCK_ACCESS_FS_TRUNCATE: Truncate a file through file truncation APIs > + * like :manpage:`truncate(2)`, :manpage:`ftruncate(2)`, or > + * :manpage:`open(2)` with O_TRUNC or :manpage:`creat(2)`. This access right > + * is available since the third version of the Landlock ABI. > * > * A directory can receive access rights related to files or directories. The > * following access right is applied to the directory itself, and the > @@ -139,10 +146,9 @@ struct landlock_path_beneath_attr { > * > * It is currently not possible to restrict some file-related actions > * accessible through these syscall families: :manpage:`chdir(2)`, > - * :manpage:`truncate(2)`, :manpage:`stat(2)`, :manpage:`flock(2)`, > - * :manpage:`chmod(2)`, :manpage:`chown(2)`, :manpage:`setxattr(2)`, > - * :manpage:`utime(2)`, :manpage:`ioctl(2)`, :manpage:`fcntl(2)`, > - * :manpage:`access(2)`. > + * :manpage:`stat(2)`, :manpage:`flock(2)`, :manpage:`chmod(2)`, > + * :manpage:`chown(2)`, :manpage:`setxattr(2)`, :manpage:`utime(2)`, > + * :manpage:`ioctl(2)`, :manpage:`fcntl(2)`, :manpage:`access(2)`. > * Future Landlock evolutions will enable to restrict them. > */ > /* clang-format off */