netdev - Re: [RFC PATCH 0/1] lsm: Add hook unix_path

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Message-ID: <CAAVpQUCF3uES6j22P1TYzgKByw+E4EqpM=+OFyqtRGStGWxH+Q@mail.gmail.com>
Date: Sun, 4 Jan 2026 23:46:46 -0800
From: Kuniyuki Iwashima <kuniyu@...gle.com>
To: Justin Suess <utilityemal77@...il.com>
Cc: Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>, 
	"Serge E . Hallyn" <serge@...lyn.com>, Simon Horman <horms@...nel.org>, 
	Mickaël Salaün <mic@...ikod.net>, 
	Günther Noack <gnoack@...gle.com>, 
	linux-security-module@...r.kernel.org, Tingmao Wang <m@...wtm.org>, 
	netdev@...r.kernel.org
Subject: Re: [RFC PATCH 0/1] lsm: Add hook unix_path_connect

On Wed, Dec 31, 2025 at 1:33 PM Justin Suess <utilityemal77@...il.com> wrote:
>
> Hi,
>
> This patch introduces a new LSM hook unix_path_connect.
>
> The idea for this patch and the hook came from Günther Noack, who
> is cc'd. Much credit to him for the idea and discussion.
>
> This patch is based on the lsm next branch.
>
> Motivation
> ---
>
> For AF_UNIX sockets bound to a filesystem path (aka named sockets), one
> identifying object from a policy perspective is the path passed to
> connect(2). However, this operation currently restricts LSMs that rely
> on VFS-based mediation, because the pathname resolved during connect()
> is not preserved in a form visible to existing hooks before connection
> establishment.

Why can't LSM use unix_sk(other)->path in security_unix_stream_connect()
and security_unix_may_send() ?


> As a result, LSMs such as Landlock cannot currently
> restrict connections to named UNIX domain sockets by their VFS path.
>
> This gap has been discussed previously (e.g. in the context of Landlock's
> path-based access controls). [1] [2]
>
> I've cc'd the netdev folks as well on this, as the placement of this hook is
> important and in a core unix socket function.
>
> Design Choices
> ---
>
> The hook is called in net/unix/af_unix.c in the function unix_find_bsd().
>
> The hook takes a single parameter, a const struct path* to the named unix
> socket to which the connection is being established.
>
> The hook takes place after normal permissions checks, and after the
> inode is determined to be a socket. It however, takes place before
> the socket is actually connected to.
>
> If the hook returns non-zero it will do a put on the path, and return.
>
> References
> ---
>
> [1]: https://github.com/landlock-lsm/linux/issues/36#issue-2354007438
> [2]: https://lore.kernel.org/linux-security-module/cover.1767115163.git.m@maowtm.org/
>
> Kind Regards,
> Justin Suess
>
> Justin Suess (1):
>   lsm: Add hook unix_path_connect
>
>  include/linux/lsm_hook_defs.h |  1 +
>  include/linux/security.h      |  6 ++++++
>  net/unix/af_unix.c            |  8 ++++++++
>  security/security.c           | 16 ++++++++++++++++
>  4 files changed, 31 insertions(+)
>
>
> base-commit: 1c0860d4415d52f3ad1c8e0a15c1272869278a06
> --
> 2.51.0
>