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Date: Wed, 31 May 2017 00:56:33 +0100
From: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
To: Matt Brown <matt@nmatt.com>
Cc: Casey Schaufler <casey@schaufler-ca.com>,
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Subject: Re: [kernel-hardening] Re: [PATCH v7 2/2] security: tty: make
 TIOCSTI ioctl require CAP_SYS_ADMIN
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> This is my point. Apps will continue to shoot themselves in the foot. Of course
> the correct response to one of these vulns is to not pass ttys across a
> security boundary. We have an opportunity here to reduce the impact of this bug
> class at the kernel level. 

Not really.

If you pass me your console for example I can mmap your framebuffer and
spy on you all day. Or I could reprogram your fonts, your keyboard, your
video mode, or use set and paste selection to write stuff. If you are
using X and you can't get tty handles right you'll no doubt pass me a
copy of your X file descriptor in which case I own your display, your
keyboard and your mouse and I don't need to use TIOCSTI there either.

There are so many different attacks based upon that screwup that the
kernel cannot defend against them. You aren't exactly reducing the impact.

Alan