linux-kernel - Re: [PATCH 08/11] gfs2: reorder capability check last

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Message-ID: <CAHc6FU5t0cB=+9ijwx26NUEck1YS7304ue_5FRwqXRzBq14jjA@mail.gmail.com>
Date: Mon, 25 Nov 2024 12:34:02 +0100
From: Andreas Gruenbacher <agruenba@...hat.com>
To: cgzones@...glemail.com
Cc: linux-security-module@...r.kernel.org, Serge Hallyn <serge@...lyn.com>, 
	Julia Lawall <Julia.Lawall@...ia.fr>, Nicolas Palix <nicolas.palix@...g.fr>, 
	linux-kernel@...r.kernel.org, gfs2@...ts.linux.dev, cocci@...ia.fr
Subject: Re: [PATCH 08/11] gfs2: reorder capability check last

On Mon, Nov 25, 2024 at 11:46 AM Christian Göttsche
<cgoettsche@...tendoof.de> 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>
> ---
>  fs/gfs2/quota.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/gfs2/quota.h b/fs/gfs2/quota.h
> index f462d9cb3087..988f38dc5b2c 100644
> --- a/fs/gfs2/quota.h
> +++ b/fs/gfs2/quota.h
> @@ -44,8 +44,8 @@ static inline int gfs2_quota_lock_check(struct gfs2_inode *ip,
>         int ret;
>
>         ap->allowed = UINT_MAX; /* Assume we are permitted a whole lot */
> -       if (capable(CAP_SYS_RESOURCE) ||
> -           sdp->sd_args.ar_quota == GFS2_QUOTA_OFF)
> +       if (sdp->sd_args.ar_quota == GFS2_QUOTA_OFF ||
> +           capable(CAP_SYS_RESOURCE))
>                 return 0;
>         ret = gfs2_quota_lock(ip, NO_UID_QUOTA_CHANGE, NO_GID_QUOTA_CHANGE);
>         if (ret)
> --
> 2.45.2

Applied, thanks.

Andreas