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 C7438C77B73 for ; Sun, 16 Apr 2023 16:13:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230110AbjDPQNe (ORCPT ); Sun, 16 Apr 2023 12:13:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55232 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230329AbjDPQNd (ORCPT ); Sun, 16 Apr 2023 12:13:33 -0400 Received: from smtp-bc08.mail.infomaniak.ch (smtp-bc08.mail.infomaniak.ch [IPv6:2001:1600:4:17::bc08]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 51C303595 for ; Sun, 16 Apr 2023 09:13:30 -0700 (PDT) Received: from smtp-2-0000.mail.infomaniak.ch (unknown [10.5.36.107]) by smtp-3-3000.mail.infomaniak.ch (Postfix) with ESMTPS id 4PzwGJ41rmzMqCyp; Sun, 16 Apr 2023 18:13:28 +0200 (CEST) Received: from unknown by smtp-2-0000.mail.infomaniak.ch (Postfix) with ESMTPA id 4PzwGH32D6zMppDR; Sun, 16 Apr 2023 18:13:27 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=digikod.net; s=20191114; t=1681661608; bh=wvZktsS2wovttTPKhuIKuxoQ9kE6pVtEyePlXYSAocU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=snAwV5HoppK8rU92IrbLQPI5kLV4FAtdWXM9erbn4J9qeDk+8dQ+TJHb00MyqtEh/ WWFcQr5dQ/atS6nigS2oSoWuaoe6EpEskhGukpXD6ZHzsEkN51aXdqj+5XJyyHYxiV ZY0HpqHtIscLGKWaBGYEraSZDp4v85AdMvL5l4Wk= Message-ID: Date: Sun, 16 Apr 2023 18:13:32 +0200 MIME-Version: 1.0 User-Agent: Subject: Re: [PATCH v10 13/13] landlock: Document Landlock's network support Content-Language: en-US To: Konstantin Meskhidze Cc: willemdebruijn.kernel@gmail.com, gnoack3000@gmail.com, linux-security-module@vger.kernel.org, netdev@vger.kernel.org, netfilter-devel@vger.kernel.org, yusongping@huawei.com, artem.kuzin@huawei.com References: <20230323085226.1432550-1-konstantin.meskhidze@huawei.com> <20230323085226.1432550-14-konstantin.meskhidze@huawei.com> From: =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= In-Reply-To: <20230323085226.1432550-14-konstantin.meskhidze@huawei.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Infomaniak-Routing: alpha Precedence: bulk List-ID: On 23/03/2023 09:52, Konstantin Meskhidze wrote: > Describe network access rules for TCP sockets. Add network access > example in the tutorial. Add kernel configuration support for network. > > Signed-off-by: Konstantin Meskhidze > --- > > Changes since v9: > * Minor refactoring. > > Changes since v8: > * Minor refactoring. > > Changes since v7: > * Fixes documentaion logic errors and typos as Mickaёl suggested: > https://lore.kernel.org/netdev/9f354862-2bc3-39ea-92fd-53803d9bbc21@digikod.net/ > > Changes since v6: > * Adds network support documentaion. > > --- > Documentation/userspace-api/landlock.rst | 69 ++++++++++++++++++------ > 1 file changed, 54 insertions(+), 15 deletions(-) > > diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst > index f6a7da21708a..0d640bfa3126 100644 > --- a/Documentation/userspace-api/landlock.rst > +++ b/Documentation/userspace-api/landlock.rst > @@ -11,10 +11,10 @@ Landlock: unprivileged access control > :Date: October 2022 > > The goal of Landlock is to enable to restrict ambient rights (e.g. global > -filesystem access) for a set of processes. Because Landlock is a stackable > -LSM, it makes possible to create safe security sandboxes as new security layers > -in addition to the existing system-wide access-controls. This kind of sandbox > -is expected to help mitigate the security impact of bugs or > +filesystem or network access) for a set of processes. Because Landlock > +is a stackable LSM, it makes possible to create safe security sandboxes as new > +security layers in addition to the existing system-wide access-controls. This > +kind of sandbox is expected to help mitigate the security impact of bugs or > unexpected/malicious behaviors in user space applications. Landlock empowers > any process, including unprivileged ones, to securely restrict themselves. > > @@ -30,8 +30,9 @@ Landlock rules > > A Landlock rule describes an action on an object. An object is currently a A Landlock rule describes an action on a kernel object. Filesystem objects can be defined with a file hierarchy. Since the fourth ABI version, TCP ports enable to identify inbound or outbound connections. Actions on these kernel objects are defined according to `access rights`_. A set of rules… > file hierarchy, and the related filesystem actions are defined with `access > -rights`_. A set of rules is aggregated in a ruleset, which can then restrict > -the thread enforcing it, and its future children. > +rights`_. Since ABI version 4 a port data appears with related network actions > +for TCP socket families. A set of rules is aggregated in a ruleset, which > +can then restrict the thread enforcing it, and its future children. > > Defining and enforcing a security policy > ---------------------------------------- > @@ -41,7 +42,8 @@ example, the ruleset will contain rules that only allow read actions, but write "the ruleset will contain rules that only allow filesystem read actions and establish a specific TCP connection, but filesystem write actions and other TCP actions will be denied." > actions will be denied. The ruleset then needs to handle both of these kind of > actions. This is required for backward and forward compatibility (i.e. the > kernel and user space may not know each other's supported restrictions), hence > -the need to be explicit about the denied-by-default access rights. > +the need to be explicit about the denied-by-default access rights. Also, ruleset > +will have network rules for specific ports, so it should handle network actions. This hunk can then be removed. > > .. code-block:: c > > @@ -62,6 +64,9 @@ the need to be explicit about the denied-by-default access rights. > LANDLOCK_ACCESS_FS_MAKE_SYM | > LANDLOCK_ACCESS_FS_REFER | > LANDLOCK_ACCESS_FS_TRUNCATE, > + .handled_access_net = > + LANDLOCK_ACCESS_NET_BIND_TCP | > + LANDLOCK_ACCESS_NET_CONNECT_TCP, > }; > > Because we may not know on which kernel version an application will be > @@ -70,14 +75,18 @@ should try to protect users as much as possible whatever the kernel they are > using. To avoid binary enforcement (i.e. either all security features or > none), we can leverage a dedicated Landlock command to get the current version > of the Landlock ABI and adapt the handled accesses. Let's check if we should > -remove the ``LANDLOCK_ACCESS_FS_REFER`` or ``LANDLOCK_ACCESS_FS_TRUNCATE`` > -access rights, which are only supported starting with the second and third > -version of the ABI. > +remove the ``LANDLOCK_ACCESS_FS_REFER`` or ``LANDLOCK_ACCESS_FS_TRUNCATE`` or > +network access rights, which are only supported starting with the second, > +third and fourth version of the ABI. > > .. code-block:: c > > int abi; > > + #define ACCESS_NET_BIND_CONNECT ( \ > + LANDLOCK_ACCESS_NET_BIND_TCP | \ > + LANDLOCK_ACCESS_NET_CONNECT_TCP) > + > abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION); > if (abi < 0) { > /* Degrades gracefully if Landlock is not handled. */ > @@ -92,6 +101,11 @@ version of the ABI. > case 2: > /* Removes LANDLOCK_ACCESS_FS_TRUNCATE for ABI < 3 */ > ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE; > + case 3: > + /* Removes network support for ABI < 4 */ > + ruleset_attr.handled_access_net &= > + ~(LANDLOCK_ACCESS_NET_BIND_TCP | > + LANDLOCK_ACCESS_NET_CONNECT_TCP); > } > > This enables to create an inclusive ruleset that will contain our rules. > @@ -143,10 +157,23 @@ for the ruleset creation, by filtering access rights according to the Landlock > ABI version. In this example, this is not required because all of the requested > ``allowed_access`` rights are already available in ABI 1. > > -We now have a ruleset with one rule allowing read access to ``/usr`` while > -denying all other handled accesses for the filesystem. The next step is to > -restrict the current thread from gaining more privileges (e.g. thanks to a SUID > -binary). > +For network access-control, we can add a set of rules that allow to use a port > +number for a specific action. It would be more useful to change this example with a TCP connection to port 443 and explain that it will only allow to connect to HTTPS services. "…for a specific action: HTTPS connections." > + > +.. code-block:: c > + > + struct landlock_net_service_attr net_service = { > + .allowed_access = LANDLOCK_ACCESS_NET_BIND_TCP, NET_CONNECT_TCP > + .port = 8080, 443 > + }; > + > + err = landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_SERVICE, > + &net_service, 0); > + > +The next step is to restrict the current thread from gaining more privileges > +(e.g. through a SUID binary). We now have a ruleset with the first rule allowing > +read access to ``/usr`` while denying all other handled accesses for the filesystem, > +and a second rule allowing TCP binding on port 8080. "allowing HTTPS connections." > > .. code-block:: c > > @@ -355,7 +382,7 @@ Access rights > ------------- > > .. kernel-doc:: include/uapi/linux/landlock.h > - :identifiers: fs_access > + :identifiers: fs_access net_access > > Creating a new ruleset > ---------------------- > @@ -374,6 +401,7 @@ Extending a ruleset > > .. kernel-doc:: include/uapi/linux/landlock.h > :identifiers: landlock_rule_type landlock_path_beneath_attr > + landlock_net_service_attr > > Enforcing a ruleset > ------------------- > @@ -451,6 +479,12 @@ always allowed when using a kernel that only supports the first or second ABI. > 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. > > +Network support (ABI < 4) > +------------------------- > + > +Starting with the Landlock ABI version 4, it is now possible to restrict TCP > +bind and connect actions to only a set of allowed ports. > + > .. _kernel_support: > > Kernel support > @@ -469,6 +503,11 @@ still enable it by adding ``lsm=landlock,[...]`` to > Documentation/admin-guide/kernel-parameters.rst thanks to the bootloader > configuration. > > +To be able to explicitly allow TCP operations (e.g., adding a network rule with > +``LANDLOCK_ACCESS_NET_TCP_BIND``), the kernel must support TCP (``CONFIG_INET=y``). > +Otherwise, sys_landlock_add_rule() returns an ``EAFNOSUPPORT`` error, which can > +safely be ignored because this kind of TCP operation is already not possible. > + > Questions and answers > ===================== > > -- > 2.25.1 >