linux-kernel - Re: [RFC][PATCH] sysctl: Remove the sysctl system call

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Message-ID: <87imp8hyc8.fsf@x220.int.ebiederm.org>
Date:   Tue, 01 Oct 2019 17:53:27 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-api@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andi Kleen <andi@...stfloor.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Apelete Seketeli <apelete@...eteli.net>,
        Arnd Bergmann <arnd@...db.de>,
        Chee Nouk Phoon <cnphoon@...era.com>,
        Chris Zankel <chris@...kel.net>,
        Christian Ruppert <christian.ruppert@...lis.com>,
        Greg Ungerer <gerg@...inux.org>, Helge Deller <deller@....de>,
        Hongliang Tao <taohl@...ote.com>,
        Huacai Chen <chenhc@...ote.com>,
        Jonas Jensen <jonas.jensen@...il.com>,
        Josh Boyer <jwboyer@...il.com>, Jun Nie <jun.nie@...aro.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Ley Foon Tan <lftan@...era.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Max Filippov <jcmvbkbc@...il.com>,
        Olof Johansson <olof@...om.net>,
        Paul Burton <paul.burton@...s.com>,
        Phil Edworthy <phil.edworthy@...esas.com>,
        Pierrick Hascoet <pierrick.hascoet@...lis.com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Roland Stigge <stigge@...com.de>,
        Vineet Gupta <vgupta@...opsys.com>
Subject: Re: [RFC][PATCH] sysctl: Remove the sysctl system call

Kees Cook <keescook@...omium.org> writes:

> On Tue, Oct 01, 2019 at 01:36:32PM -0500, Eric W. Biederman wrote:
>> 
>> This system call has been deprecated almost since it was introduced, and
>> in a survey of the linux distributions I can no longer find any of them
>> that enable CONFIG_SYSCTL_SYSCALL.  The only indication that I can find
>> that anyone might care is that a few of the defconfigs in the kernel
>> enable CONFIG_SYSCTL_SYSCALL.  However this appears in only 31 of 414
>> defconfigs in the kernel, so I suspect this symbols presence is simply
>> because it is harmless to include rather than because it is necessary.
>> 
>> As there appear to be no users of the sysctl system call, remove the
>> code.  As this removes one of the few uses of the internal kernel mount
>> of proc I hope this allows for even more simplifications of the proc
>> filesystem.
>
> I'm for it. :) I tripped over this being deprecated over a decade ago. :P
>
> I think you can actually take this further and remove (or at least
> empty) the uapi/linux/sysctl.h file too.

I copied everyone who had put this into a defconfig and I will wait a
little more to see if anyone screams.  I think it is a safe guess that
several of the affected configurations are dead (or at least
unmaintained) as I received 17 bounces when copying everyone.

I would make it a followup that removes uapi/linux/sysctl.h.  I don't
see anything in it that isn't about the sysctl system call.  I will keep
it a separate patch as I can imagine something silly that needs the
header file to compile.  A separate patch would make a revert easier
if we find something like that.

Eric