linux-kernel - Re: [PATCH] Allow restricting permissions in /proc/sys

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Date:   Sun, 3 Nov 2019 21:24:27 +0200
From:   Topi Miettinen <toiwoton@...il.com>
To:     "Theodore Y. Ts'o" <tytso@....edu>
Cc:     Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:FILESYSTEMS (VFS and infrastructure)" 
        <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] Allow restricting permissions in /proc/sys

On 3.11.2019 19.56, 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@...il.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?

That could make sense, in addition changing UID/GID would allow even 
more flexibility. The current checks and restrictions which prevent 
those changes were already present in original code in 2007. I didn't 
want to change the logic too much. Perhaps loosening the restrictions 
could be a follow-up patch, as it may give chance to use more of generic 
proc or fslib code and thus a larger restructuring.

-Topi