From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter =?utf-8?q?M=C3=BCller?= <peter.mueller@ipfire.org>
To: development@lists.ipfire.org
Subject: Re: [PATCH] sysctl.conf: prevent autoloading of TTY line disciplines
Date: Fri, 02 Apr 2021 21:30:53 +0200
Message-ID: <92f0b0b7-530f-214f-d14f-9d8c9cbb60d7@ipfire.org>
In-Reply-To: <2c3adcb9-d6e1-ba67-41fa-ae1c4bce3527@ipfire.org>
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Hello Michael,

it seems as the kernel folks backported this into 4.14.x by now:

> [root(a)maverick ~]# uname -a
> Linux maverick 4.14.212-ipfire #1 SMP Wed Dec 16 12:01:25 GMT 2020 x86_64 I=
ntel(R) Celeron(R) CPU N3150 @ 1.60GHz GenuineIntel GNU/Linux
> [root(a)maverick ~]# sysctl dev.tty.ldisc_autoload
> dev.tty.ldisc_autoload =3D 1

Therefore, I would like to see this patch being merged - that is, if it is st=
ill applicable. :-)

Thanks, and best regards,
Peter M=C3=BCller


> Hello Michael,
>=20
> grmpf, overlooked some patched distribution kernel again. :-/
>=20
> Sorry for the noise - I will keep the patch queued and wait for kernel 5.9 =
...
>=20
> Thanks, and best regards,
> Peter M=C3=BCller
>=20
>=20
>> This does not exist before kernel 5.1.
>>
>> -Michael
>>
>>> On 5 Oct 2020, at 20:45, Peter M=C3=BCller <peter.mueller(a)ipfire.org> w=
rote:
>>>
>>> Malicious/vulnerable TTY line disciplines have been subject of some
>>> kernel exploits such as CVE-2017-2636, and since - to put it in Greg
>>> Kroah-Hatrman's words - we do not "trust the userspace to do the right
>>> thing", this reduces local kernel attack surface.
>>>
>>> Further, there is no legitimate reason why an unprivileged user should
>>> load kernel modules during runtime, anyway.
>>>
>>> See also:
>>> - https://lkml.org/lkml/2019/4/15/890
>>> - https://a13xp0p0v.github.io/2017/03/24/CVE-2017-2636.html
>>>
>>> Cc: Arne Fitzenreiter <arne.fitzenreiter(a)ipfire.org>
>>> Cc: Michael Tremer <michael.tremer(a)ipfire.org>
>>> Signed-off-by: Peter M=C3=BCller <peter.mueller(a)ipfire.org>
>>> ---
>>> config/etc/sysctl.conf | 4 ++++
>>> 1 file changed, 4 insertions(+)
>>>
>>> diff --git a/config/etc/sysctl.conf b/config/etc/sysctl.conf
>>> index d48c7734e..b5ede15ed 100644
>>> --- a/config/etc/sysctl.conf
>>> +++ b/config/etc/sysctl.conf
>>> @@ -39,6 +39,10 @@ net.bridge.bridge-nf-call-ip6tables =3D 0
>>> net.bridge.bridge-nf-call-iptables =3D 0
>>> net.bridge.bridge-nf-call-arptables =3D 0
>>>
>>> +# Restrict loading TTY line disciplines to CAP_SYS_MODULE to prevent unp=
rivileged attackers
>>> +# from loading vulnerable line disciplines with the TIOCSETD ioctl.
>>> +dev.tty.ldisc_autoload =3D 0
>>> +
>>> # Try to keep kernel address exposures out of various /proc files (kallsy=
ms, modules, etc).
>>> kernel.kptr_restrict =3D 2
>>>
>>> --=20
>>> 2.26.2
>>

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