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

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Date:   Wed, 21 Feb 2018 10:33:58 -0500
From:   Waiman Long <longman@...hat.com>
To:     Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     "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 02/20/2018 08:26 PM, Kees Cook wrote:
> 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
>
My current thinking is to issue at most one warning per sysctl parameter
as additional warning of the same kind does not provide additional
information.

-Longman