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

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Message-ID: <ee3ec63269b43b34e1c90dd8c9743bf8@finder.org>
Date: Fri, 29 Nov 2024 11:33:31 -0800
From: Jared Finder <jared@...der.org>
To: linux-hardening@...r.kernel.org
Subject: GPM & Emacs broken in Linux 6.7 -- ok to relax check?

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/. 
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.

Thank you for your time.

   -- MJF