linux-kernel - Re: [PATCH 2/3] sysctl: Warn when a clamped sysctl parameter is set out of range

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Date:   Tue, 20 Feb 2018 17:26:25 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Waiman Long <longman@...hat.com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 2/3] sysctl: Warn when a clamped sysctl parameter is set
 out of range

On Tue, Feb 20, 2018 at 3:17 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Mon, 19 Feb 2018 11:53:50 -0500 Waiman Long <longman@...hat.com> wrote:
>
>> Even with clamped sysctl parameters, it is still not that straight
>> forward to figure out the exact range of those parameters. One may
>> try to write extreme parameter values to see if they get clamped.
>> To make it easier, a warning with the expected range will now be
>> printed in the kernel ring buffer when a clamped sysctl parameter
>> receives an out of range value.
>
> This assumes that do_proc_dointvec_minmax_conv() and
> do_proc_douintvec_minmax_conv() are only ever called by privileged
> userspace.  Because we mustn't give unprivileged applications a way to
> spam the kernel logs.
>
> That's presumably true in the case of the caller you just added, but I
> don't see what we can do to guarantee this in the future, so perhaps we
> should add some permission check to the pr_warn()?

How about pr_warn_ratelimited() instead?

-Kees

-- 
Kees Cook
Pixel Security