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

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Message-Id: <20180220151705.8b4519f105db8f5c119015f0@linux-foundation.org>
Date:   Tue, 20 Feb 2018 15:17:05 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Waiman Long <longman@...hat.com>
Cc:     "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...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 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()?