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Date: Tue, 10 Oct 2023 08:17:42 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Kees Cook <keescook@...omium.org>
Cc: Günther Noack <gnoack@...gle.com>,
Samuel Thibault <samuel.thibault@...-lyon.org>,
Hanno Böck <hanno@...eck.de>,
kernel-hardening@...ts.openwall.com,
Jiri Slaby <jirislaby@...nel.org>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
Paul Moore <paul@...l-moore.com>,
David Laight <David.Laight@...lab.com>,
Simon Brand <simon.brand@...tadigitale.de>,
Dave Mielke <Dave@...lke.cc>,
Mickaël Salaün <mic@...ikod.net>,
KP Singh <kpsingh@...gle.com>,
Nico Schottelius <nico-gpm2008@...ottelius.org>
Subject: Re: [PATCH v3 0/1] Restrict access to TIOCLINUX
On Mon, Oct 09, 2023 at 01:19:47PM -0700, Kees Cook wrote:
> On Fri, Sep 15, 2023 at 03:32:29PM +0200, Günther Noack wrote:
> > On Tue, Aug 29, 2023 at 03:00:19PM +0200, Günther Noack wrote:
> > > Let me update the list of known usages then: The TIOCL_SETSEL, TIOCL_PASTESEL
> > > and TIOCL_SELLOADLUT mentions found on codesearch.debian.net are:
> > >
> > > (1) Actual invocations:
> > >
> > > * consolation:
> > > "consolation" is a gpm clone, which also runs as root.
> > > (I have not had the chance to test this one yet.)
> >
> > I have tested the consolation program with a kernel that has the patch, and it
> > works as expected -- you can copy and paste on the console.
> >
> >
> > > * BRLTTY:
> > > Uses TIOCL_SETSEL as a means to highlight portions of the screen.
> > > The TIOCSTI patch made BRLTTY work by requiring CAP_SYS_ADMIN,
> > > so we know that BRLTTY has that capability (it runs as root and
> > > does not drop it).
> > >
> > > (2) Some irrelevant matches:
> > >
> > > * snapd: has a unit test mentioning it, to test their seccomp filters
> > > * libexplain: mentions it, but does not call it (it's a library for
> > > human-readably decoding system calls)
> > > * manpages: documentation
> > >
> > >
> > > *Outside* of codesearch.debian.org:
> > >
> > > * gpm:
> > > I've verified that this works with the patch.
> > > (To my surprise, Debian does not index this project's code.)
> >
> > (As Samuel pointed out, I was wrong there - Debian does index it, but it does
> > not use the #defines from the headers... who would have thought...)
> >
> >
> > > FWIW, I also briefly looked into "jamd" (https://jamd.sourceforge.net/), which
> > > was mentioned as similar in the manpage for "consolation", but that software
> > > does not use any ioctls at all.
> > >
> > > So overall, it still seems like nothing should break. 👍
> >
> > Summarizing the above - the only three programs which are known to use the
> > affected TIOCLINUX subcommands are:
> >
> > * consolation (tested)
> > * gpm (tested)
> > * BRLTTY (known to work with TIOCSTI, where the same CAP_SYS_ADMIN requirement
> > is imposed for a while now)
> >
> > I think that this is a safe change for the existing usages and that we have done
> > the due diligence required to turn off these features.
> >
> > Greg, could you please have another look?
>
> Can you spin a v4 with all these details collected into the commit log?
> That should be sufficient information for Greg, I would think.
This is already commit 8d1b43f6a6df ("tty: Restrict access to TIOCLINUX'
copy-and-paste subcommands") in my tty-next tree, and in linux-next.
It's been there for 5 days now :)
thanks,
greg k-h
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