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Date:   Fri, 14 Oct 2022 19:51:11 +0000
From:   Simon Brand <>
Subject: Reconsider possibility to disable icotl TIOCSTI

Good day,

please reconsider to add a possibility to disable icotl TIOCSTI.
In the past there have been attempts to restrict the TIOCSTI ioctl. [0, 1]
None of them are present in the current kernel.
Since those tries there have been some security issues (sandbox
escapes in flatpak (CVE-2019-10063) [2] and snap (CVE 2019-7303) [3],
runuser [4], su [5]).

I ask to merge the patches from linux-hardening [6, 7] so users can
opt out of this behavior. These patches provide the
`SECURITY_TIOCSTI_RESTRICT` Kconfig (default no) and a
`tiocsti_restrict` sysctl.

Escapes can be reproduced easiliy (on archlinux) via a python script:
import fcntl
import termios
with open("/dev/tty", "w") as fd:
    for c in "id\n":
        fcntl.ioctl(fd, termios.TIOCSTI, c)
Now run as root:
# su user
$ python3 /path/to/ ; exit
uid=0(root) ...

I asked it before on kernelnewbies mailing list. [8]

Best and thank you,


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