linux-kernel - Re: [PATCH] make TIOCSTI ioctl require CAP_SYS

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Message-ID: <4a7ab5c3-590e-891f-61ce-534483dc2ec6@nmatt.com>
Date:   Wed, 19 Apr 2017 20:08:02 -0400
From:   Matt Brown <matt@...tt.com>
To:     James Morris <jmorris@...ei.org>
Cc:     serge@...lyn.com, gregkh@...uxfoundation.org, jslaby@...e.com,
        akpm@...ux-foundation.org, jannh@...gle.com, keescook@...omium.org,
        kernel-hardening@...ts.openwall.com,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] make TIOCSTI ioctl require CAP_SYS_ADMIN

On 04/19/2017 07:18 AM, James Morris wrote:
> On Tue, 18 Apr 2017, Matt Brown wrote:
>
>> This patch reproduces GRKERNSEC_HARDEN_TTY functionality from the grsecurity
>> project in-kernel.
>
> It seems like an ugly hack to an ugly feature (CAP_SYS_ADMIN barely makes
> sense here), and rather than sprinkling these types of things throughout
> the kernel, I wonder if it might be better to implement it via LSM, in the
> YAMA module.
>
>

CAP_SYS_ADMIN is already used in the TIOCSTI TTY code to allow
character insertion into TTYs other than the caller's controlling
terminal. This is done because different TTYs indicate a security
boundary that should only be able to be crossed by a privileged
process. This patch would merely extend this security boundary
protection to include unprivileged processes from utilizing a common
TTY to step across a security boundary.

>
> - James
>