linux-kernel - Re: [kernel-hardening] Re: [PATCH v7 2/2] security: tty: make TIOCSTI ioctl require CAP_SYS

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Message-ID: <99069e11-dc84-8198-5d1c-f39b18ac9971@nmatt.com>
Date:   Tue, 30 May 2017 19:00:09 -0400
From:   Matt Brown <matt@...tt.com>
To:     Daniel Micay <danielmicay@...il.com>,
        Nick Kralevich <nnk@...gle.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        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>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        kernel-hardening@...ts.openwall.com,
        linux-security-module <linux-security-module@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [kernel-hardening] Re: [PATCH v7 2/2] security: tty: make TIOCSTI
 ioctl require CAP_SYS_ADMIN

On 5/30/17 4:22 PM, Daniel Micay wrote:
>> Thanks, I didn't know that android was doing this. I still think this
>> feature
>> is worthwhile for people to be able to harden their systems against
>> this attack
>> vector without having to implement a MAC.
> 
> Since there's a capable LSM hook for ioctl already, it means it could go
> in Yama with ptrace_scope but core kernel code would still need to be
> changed to track the owning tty. I think Yama vs. core kernel shouldn't
> matter much anymore due to stackable LSMs.
> 

What does everyone think about a v8 that moves this feature under Yama and uses
the file_ioctl LSM hook?

> Not the case for perf_event_paranoid=3 where a) there's already a sysctl
> exposed which would be unfortunate to duplicate, b) there isn't an LSM
> hook yet (AFAIK).
> 
> The toggles for ptrace and perf events are more useful though since
> they're very commonly used debugging features vs. this obscure, rarely
> used ioctl that in practice no one will notice is missing. It's still
> friendlier to have a toggle than a seccomp policy requiring a reboot to
> get rid of it, or worse compiling it out of the kernel.
>