Messages in this thread | | | Date | Tue, 27 Dec 2022 19:32:55 -0800 | From | Kees Cook <> | Subject | Re: [PATCH v3 2/2] tty: Allow TIOCSTI to be disabled |
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On December 27, 2022 3:40:00 PM PST, Samuel Thibault <samuel.thibault@aquilenet.fr> wrote: >Hello, > >Kees Cook, le sam. 22 oct. 2022 11:29:49 -0700, a ecrit: >> TIOCSTI continues its long history of being used in privilege escalation >> attacks[1]. Prior attempts to provide a mechanism to disable this have >> devolved into discussions around creating full-blown LSMs to provide >> arbitrary ioctl filtering, which is hugely over-engineered -- only >> TIOCSTI is being used this way. 3 years ago OpenBSD entirely removed >> TIOCSTI[2], Android has had it filtered for longer[3], and the tools that >> had historically used TIOCSTI either do not need it, are not commonly >> built with it, or have had its use removed. > >No. The Brltty screen reader entirely relies on TIOCSTI to be able to >support input from various Braille devices. Please make sure to keep >TIOCSTI enabled by default, otherwise some people would just completely >lose their usual way of simply typing on Linux.
Yup, it remains default enabled:
> [...] >> +config LEGACY_TIOCSTI >> + bool "Allow legacy TIOCSTI usage" >> + default y >> + help >> + Historically the kernel has allowed TIOCSTI, which will push >> + characters into a controlling TTY. This continues to be used >> + as a malicious privilege escalation mechanism, and provides no >> + meaningful real-world utility any more. > >Yes it does.
Can you send a patch to adjust this language?
Also, what does FreeBSD use for screen readers?
-Kees
-- Kees Cook
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