linux-kernel - Re: [PATCH 09/11] fs: reorder capability check last

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Message-ID: <20241125-rausch-sprossen-2570a6fe045a@brauner>
Date: Mon, 25 Nov 2024 13:17:31 +0100
From: Christian Brauner <brauner@...nel.org>
To: cgzones@...glemail.com
Cc: linux-security-module@...r.kernel.org, 
	Chuck Lever <chuck.lever@...cle.com>, Jeff Layton <jlayton@...nel.org>, 
	Amir Goldstein <amir73il@...il.com>, Alexander Viro <viro@...iv.linux.org.uk>, 
	Jan Kara <jack@...e.cz>, Serge Hallyn <serge@...lyn.com>, 
	Julia Lawall <Julia.Lawall@...ia.fr>, Nicolas Palix <nicolas.palix@...g.fr>, 
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org, 
	cocci@...ia.fr
Subject: Re: [PATCH 09/11] fs: reorder capability check last

On Mon, Nov 25, 2024 at 11:40:01AM +0100, Christian Göttsche wrote:
> From: Christian Göttsche <cgzones@...glemail.com>
> 
> capable() calls refer to enabled LSMs whether to permit or deny the
> request.  This is relevant in connection with SELinux, where a
> capability check results in a policy decision and by default a denial
> message on insufficient permission is issued.
> It can lead to three undesired cases:
>   1. A denial message is generated, even in case the operation was an
>      unprivileged one and thus the syscall succeeded, creating noise.
>   2. To avoid the noise from 1. the policy writer adds a rule to ignore
>      those denial messages, hiding future syscalls, where the task
>      performs an actual privileged operation, leading to hidden limited
>      functionality of that task.
>   3. To avoid the noise from 1. the policy writer adds a rule to permit
>      the task the requested capability, while it does not need it,
>      violating the principle of least privilege.
> 
> Signed-off-by: Christian Göttsche <cgzones@...glemail.com>
> ---

Reviewed-by: Christian Brauner <brauner@...nel.org>