linux-kernel - Re: [PATCH] landlock: Use f_cred in security_file

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Date: Thu, 7 Mar 2024 09:54:22 -0800
From: Kees Cook <keescook@...omium.org>
To: Mickaël Salaün <mic@...ikod.net>
Cc: Christian Brauner <brauner@...nel.org>,
	Günther Noack <gnoack@...gle.com>,
	Jann Horn <jannh@...gle.com>, Paul Moore <paul@...l-moore.com>,
	Konstantin Meskhidze <konstantin.meskhidze@...wei.com>,
	"Serge E . Hallyn" <serge@...lyn.com>, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH] landlock: Use f_cred in security_file_open() hook

On Thu, Mar 07, 2024 at 10:52:03AM +0100, Mickaël Salaün wrote:
> Use landlock_cred(file->f_cred)->domain instead of
> landlock_get_current_domain() in security_file_open() hook
> implementation.
> 
> This should not change the current behavior but could avoid potential
> race conditions in case of current task's credentials change.
> 
> This will also ensure consistency with upcoming audit support relying on
> file->f_cred.
> 
> Add and use a new get_fs_domain() helper to mask non-filesystem domains.
> 
> file->f_cred is set by path_openat()/alloc_empty_file()/init_file() just
> before calling security_file_alloc().
> 
> Cc: Christian Brauner <brauner@...nel.org>
> Cc: Günther Noack <gnoack@...gle.com>
> Cc: Jann Horn <jannh@...gle.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Paul Moore <paul@...l-moore.com>
> Signed-off-by: Mickaël Salaün <mic@...ikod.net>
> Link: https://lore.kernel.org/r/20240307095203.1467189-1-mic@digikod.net

This looks sensible to me. It follows best practices[1] for avoiding
confused deputy attacks as well.

Reviewed-by: Kees Cook <keescook@...omium.org>

[1] https://docs.kernel.org/security/credentials.html?highlight=confused+deputy#open-file-credentials

-- 
Kees Cook