linux-hardening - Re: GPM & Emacs broken in Linux 6.7 -- ok to relax check?

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Message-ID: <CAG48ez0vg9W=oatvEqxvTSYNUx7htY23LxPrYCiuLZhZQuaGjg@mail.gmail.com>
Date: Fri, 29 Nov 2024 20:50:38 +0100
From: Jann Horn <jannh@...gle.com>
To: Jared Finder <jared@...der.org>, Hanno Böck <hanno@...eck.de>, 
	Günther Noack <gnoack@...gle.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jiri Slaby <jirislaby@...nel.org>
Cc: linux-hardening@...r.kernel.org, regressions@...ts.linux.dev, 
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: GPM & Emacs broken in Linux 6.7 -- ok to relax check?

+regression list, LKML, maintainers, patch authors

On Fri, Nov 29, 2024 at 8:38 PM Jared Finder <jared@...der.org> wrote:
> The change to restrict access to TIOCLINUX that was added in Linux 6.7
> breaks Emacs rendering of the mouse pointer. This change was previous
> discussed in
> https://lwn.net/ml/kernel-hardening/20230402160815.74760f87.hanno@hboeck.de/.

This landed as commit 8d1b43f6a6df ("tty: Restrict access to
TIOCLINUX' copy-and-paste subcommands").

#regzbot introduced: 8d1b43f6a6df

> An associated Emacs bug report, bug #74220, is discussed at
> https://lists.gnu.org/archive/html/bug-gnu-emacs/2024-11/msg00275.html.
>
> I wanted to ask if it made sense for the restriction to not apply to the
> following three selection modes for TIOCL_SETSEL:
>
> TIOCL_SELPOINTER   3 /* show the pointer */
> TIOCL_SELCLEAR   4 /* clear visibility of selection */
> TIOCL_SELMOUSEREPORT   16 /* report beginning of selection */
>
> On a glance over the selection code, none of these interact with
> vc_sel.buffer and therefore are unrelated to the exploit linked in the
> original report. Only SELPOINTER is necessary to be available to fix
> Emacs bug #74220. I imagine such a change would involve moving the
> capability check from tioclinux(), case TIOCL_SETSEL to inside
> vc_do_selection().
>
> Note: This is my first time emailing a Linux kernel mailing list, so
> please let me know if there's any additional conventions I should be
> following here.

FYI, for next time: There is some documentation at
https://docs.kernel.org/admin-guide/reporting-regressions.html
specifically for reporting regressions (with a focus on what to do so
that your regression report doesn't get lost).

> Thank you for your time.
>
>    -- MJF
>