linux-hardening - The regrettable demise of the TIOCSTI ioctl.

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Message-ID: <ZCfOUSZ87LaBVjq7@beta.private.mielke.cc>
Date:   Sat, 1 Apr 2023 02:25:21 -0400
From:   Dave Mielke <Dave@...lke.cc>
To:     Linux Kernel Mailing List 
        <linux-kernel%40vger.kernel.org@...a.private.mielke.cc>
Cc:     Samuel Thibault <Samuel.Thibault@...-lyon.org>
Subject: The regrettable demise of the TIOCSTI ioctl.

It seems that, starting in the 6.2 kernel (I think), there's a move underway to get rid of the TIOCSTI ioctl. The fact that the kernel configuration information says "provides no meaningful real-world utility any more" shows that the kernel developers seem to be unaware of an important subset of their users who absolutely depend on TIOCSTI.

By removing TIOCSTI, you have broken several users' *ability* to work at all with their current hardware!

The users I'm referring to are those who rely on their ability to work productively with braille devices. They use BRLTTY (see brltty.app). Most braille devices, these days, have braille keyboards. BRLTTY interprets what its users type on those braille keyboards, and uses TIOCSTI to inject those characters. Since I'm unaware of any adequate replacement for TIOCSTI, I'm asking (begging?) that this ioctl please be NOT removed.

Even disablign it isn't good because a blind user who relies on his/her braille keyboard won't be able to fix the problem by logging in and issuing the needed sysctl command (try imagining how you'd do that without your keyboard). We could distribute a brltty.conf sysctl.d file, but that isn't a great idea either given that, in
the end, it'd end up being run on all systems since BRLTTY is generally distributed.

Please understand that it simply isn't true at all that TIOCSTI has no practical use these days. It most certainly does!

Thanks for at least hearing me out.

-- 
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