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Message-ID: <20240807.uLohy7ohYo8A@digikod.net>
Date: Wed, 7 Aug 2024 17:14:11 +0200
From: Mickaël Salaün <mic@...ikod.net>
To: Tahera Fahimi <fahimitahera@...il.com>
Cc: outreachy@...ts.linux.dev, gnoack@...gle.com, paul@...l-moore.com,
jmorris@...ei.org, serge@...lyn.com, linux-security-module@...r.kernel.org,
linux-kernel@...r.kernel.org, bjorn3_gh@...tonmail.com, jannh@...gle.com,
netdev@...r.kernel.org
Subject: Re: [PATCH v8 4/4] Landlock: Document
LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET and ABI versioning
On Thu, Aug 01, 2024 at 10:02:36PM -0600, Tahera Fahimi wrote:
> Introducing LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET as an IPC scoping
> mechanism in Landlock ABI version 6, and updating ruleset_attr,
> Landlock ABI version, and access rights code blocks based on that.
>
> Signed-off-by: Tahera Fahimi <fahimitahera@...il.com>
> ---
> v8:
> - Improving documentation by specifying differences between scoped and
> non-scoped domains.
> - Adding review notes of version 7.
> - Update date
> v7:
> - Add "LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET" explanation to IPC scoping
> section and updating ABI to version 6.
> - Adding "scoped" attribute to the Access rights section.
> - In current limitation, unnamed sockets are specified as sockets that
> are not restricted.
> - Update date
> ---
> Documentation/userspace-api/landlock.rst | 33 ++++++++++++++++++++++--
> 1 file changed, 31 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst
> index 07b63aec56fa..d602567b5139 100644
> --- a/Documentation/userspace-api/landlock.rst
> +++ b/Documentation/userspace-api/landlock.rst
> @@ -8,7 +8,7 @@ Landlock: unprivileged access control
> =====================================
>
> :Author: Mickaël Salaün
> -:Date: April 2024
> +:Date: August 2024
>
> The goal of Landlock is to enable to restrict ambient rights (e.g. global
> filesystem or network access) for a set of processes. Because Landlock
> @@ -81,6 +81,8 @@ to be explicit about the denied-by-default access rights.
> .handled_access_net =
> LANDLOCK_ACCESS_NET_BIND_TCP |
> LANDLOCK_ACCESS_NET_CONNECT_TCP,
> + .scoped =
> + LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET,
> };
>
> Because we may not know on which kernel version an application will be
> @@ -119,6 +121,9 @@ version, and only use the available subset of access rights:
> case 4:
> /* Removes LANDLOCK_ACCESS_FS_IOCTL_DEV for ABI < 5 */
> ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_IOCTL_DEV;
> + case 5:
> + /* Removes LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET for ABI < 6 */
> + ruleset_attr.scoped &= ~LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET;
> }
>
> This enables to create an inclusive ruleset that will contain our rules.
> @@ -306,6 +311,23 @@ To be allowed to use :manpage:`ptrace(2)` and related syscalls on a target
> process, a sandboxed process should have a subset of the target process rules,
> which means the tracee must be in a sub-domain of the tracer.
>
> +IPC Scoping
> +-----------
> +
> +Similar to the implicit `Ptrace restrictions`_, we may want to further restrict
> +interactions between sandboxes. Each Landlock domain can be explicitly scoped
> +for a set of actions by specifying it on a ruleset. For example, if a sandboxed
> +process should not be able to :manpage:`connect(2)` to a non-sandboxed process
> +through abstract :manpage:`unix(7)` sockets, we can specify such restriction
> +with ``LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET``.
> +
> +A sandboxed process can connect to a non-sandboxed process when its domain is
> +not scoped. If a process's domain is scoped, it can only connect to processes in
...it can only connect to sockets created by proccesses in the same
scoped domain.
> +the same scoped domain.
> +
> +IPC scoping does not support Landlock rules, so if a domain is scoped, no rules
> +can be added to allow accessing to a resource outside of the scoped domain.
> +
> Truncating files
> ----------------
>
> @@ -404,7 +426,7 @@ Access rights
> -------------
>
> .. kernel-doc:: include/uapi/linux/landlock.h
> - :identifiers: fs_access net_access
> + :identifiers: fs_access net_access scope
>
> Creating a new ruleset
> ----------------------
> @@ -541,6 +563,13 @@ earlier ABI.
> Starting with the Landlock ABI version 5, it is possible to restrict the use of
> :manpage:`ioctl(2)` using the new ``LANDLOCK_ACCESS_FS_IOCTL_DEV`` right.
>
> +Abstract Unix sockets Restriction (ABI < 6)
Let's follow the capitalization used by man pages: "UNIX" instead of
"Unix".
> +--------------------------------------------
> +
> +With ABI version 6, it is possible to restrict connection to an abstract Unix socket
> +through ``LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET``, thanks to the ``scoped`` ruleset
> +attribute.
> +
> .. _kernel_support:
>
> Kernel support
> --
> 2.34.1
>
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