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Date:   Tue, 12 Nov 2019 15:15:15 -0800
From:   Kees Cook <keescook@chromium.org>
To:     "Theodore Y. Ts'o" <tytso@mit.edu>
Cc:     Topi Miettinen <toiwoton@gmail.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "open list:FILESYSTEMS (VFS and infrastructure)" 
        <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH] Allow restricting permissions in /proc/sys
Message-ID: <201911121514.DA3BEED0@keescook>
References: <74a91362-247c-c749-5200-7bdce704ed9e@gmail.com>
 <20191103175648.GA4603@mit.edu>
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On Sun, Nov 03, 2019 at 12:56:48PM -0500, Theodore Y. Ts'o wrote:
> On Sun, Nov 03, 2019 at 04:55:48PM +0200, Topi Miettinen wrote:
> > Several items in /proc/sys need not be accessible to unprivileged
> > tasks. Let the system administrator change the permissions, but only
> > to more restrictive modes than what the sysctl tables allow.
> > 
> > Signed-off-by: Topi Miettinen <toiwoton@gmail.com>
> 
> Why should restruct the system administrator from changing the
> permissions to one which is more lax than what the sysctl tables?
> 
> The system administrator is already very much trusted.  Why should we
> take that discretion away from the system administrator?

Generally speaking, they're there to provide some sense of boundary
between uid 0 and the kernel proper. I think it's correct to not allow
weakening of these permissions (which is the current state: no change at
all).

-- 
Kees Cook