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Date: Fri, 2 Jun 2017 15:22:38 -0400
From: Matt Brown <matt@...tt.com>
To: "Serge E. Hallyn" <serge@...lyn.com>,
Alan Cox <gnomes@...rguk.ukuu.org.uk>, Kees Cook <keescook@...omium.org>
Cc: Casey Schaufler <casey@...aufler-ca.com>,
Boris Lukashev <blukashev@...pervictus.com>,
Greg KH <gregkh@...uxfoundation.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
linux-security-module <linux-security-module@...r.kernel.org>,
linux-kernel <linux-kernel@...r.kernel.org>, linux-api@...r.kernel.org
Subject: Re: Re: [PATCH v7 2/2] security: tty: make TIOCSTI
ioctl require CAP_SYS_ADMIN
On 6/2/17 2:18 PM, Serge E. Hallyn wrote:
> Quoting Matt Brown (matt@...tt.com):
>> On 6/2/17 12:57 PM, Serge E. Hallyn wrote:
>>> I'm not quite sure what you're asking for here. Let me offer a precise
>>> strawman design. I'm sure there are problems with it, it's just a starting
>>> point.
>>>
>>> system-wide whitelist (for now 'may_push_chars') is full by default.
>>>
>>
>> So is may_push_chars just an alias for TIOCSTI? Or are there some
>> potential whitelist members that would map to multiple ioctls?
>
> <shrug> I'm seeing it as only TIOCSTI right now.
>
>>> By default, nothing changes - you can use those on your own tty, need
>>> CAP_SYS_ADMIN against init_user_ns otherwise.
>>>
>>> Introduce a new CAP_TTY_PRIVILEGED.
>>>
>>
>> I'm fine with this.
>>
>>> When may_push_chars is removed from the whitelist, you lose the ability
>>> to use TIOCSTI on a tty - even your own - if you do not have CAP_TTY_PRIVILEGED
>>> against the tty's user_ns.
>>>
>>
>> How do you propose storing/updating the whitelist? sysctl?
>>
>> If it is a sysctl, would each whitelist member have a sysctl?
>> e.g.: kernel.ioctlwhitelist.may_push_chars = 1
>>
>> Overall, I'm fine with this idea.
>
> That sounds reasonable. Or a securityfs file - I guess not everyone
> has securityfs, but if it were to become part of YAMA then that would
> work.
>
Yama doesn't depend on securityfs does it?
What do other people think? Should this be an addition to YAMA or its
own thing?
Alan Cox: what do you think of the above ioctl whitelisting scheme?
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