[0/2] tty: Allow TIOCSTI to be disabled

Message

Kees Cook Oct. 15, 2022, 4:16 a.m. UTC

Hi,

This is so very long over-due. We just need to do this and put an end
to this legacy operation.

Repeating the commit log from patch 2:

    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.

    Provide a simple CONFIG and global sysctl to disable this for the system
    builders who have wanted this functionality for literally decades now,
    much like the ldisc_autoload CONFIG and sysctl.

    [1] https://lore.kernel.org/linux-hardening/Y0m9l52AKmw6Yxi1@hostpad
    [2] https://undeadly.org/cgi?action=article;sid=20170701132619
    [3] https://lore.kernel.org/lkml/[e-mail]/

Thanks,

-Kees

Kees Cook (2):
  tty: Move sysctl setup into "core" tty logic
  tty: Allow TIOCSTI to be disabled

 drivers/tty/Kconfig     | 19 +++++++++++++++++
 drivers/tty/tty.h       |  2 +-
 drivers/tty/tty_io.c    | 47 +++++++++++++++++++++++++++++++++++++++--
 drivers/tty/tty_ldisc.c | 38 +--------------------------------
 4 files changed, 66 insertions(+), 40 deletions(-)