83efeeeb3d04 ("tty: Allow TIOCSTI to be disabled") broke BRLTTY's ability to simulate keypresses on the console, thus effectively breaking braille keyboards of blind users.
This restores the TIOCSTI feature for CAP_SYS_ADMIN processes, which BRLTTY is, thus fixing braille keyboards without re-opening the security issue.
Signed-off-by: Samuel Thibault samuel.thibault@ens-lyon.org Fixes: 83efeeeb3d04 ("tty: Allow TIOCSTI to be disabled")
Index: linux-6.4/drivers/tty/tty_io.c =================================================================== --- linux-6.4.orig/drivers/tty/tty_io.c +++ linux-6.4/drivers/tty/tty_io.c @@ -2276,7 +2276,7 @@ static int tiocsti(struct tty_struct *tt char ch, mbz = 0; struct tty_ldisc *ld;
- if (!tty_legacy_tiocsti) + if (!tty_legacy_tiocsti && !capable(CAP_SYS_ADMIN)) return -EIO;
if ((current->signal->tty != tty) && !capable(CAP_SYS_ADMIN))
Hi,
Thanks for your patch.
FYI: kernel test robot notices the stable kernel rule is not satisfied.
Rule: 'Cc: stable@vger.kernel.org' or 'commit <sha1> upstream.' Subject: [PATCH] TIOCSTI: always enable for CAP_SYS_ADMIN Link: https://lore.kernel.org/stable/20230701235918.kwfathbdklkyrbde%40begin
The check is based on https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
On Sun, Jul 02, 2023 at 01:59:18AM +0200, Samuel Thibault wrote:
83efeeeb3d04 ("tty: Allow TIOCSTI to be disabled") broke BRLTTY's ability to simulate keypresses on the console, thus effectively breaking braille keyboards of blind users.
This restores the TIOCSTI feature for CAP_SYS_ADMIN processes, which BRLTTY is, thus fixing braille keyboards without re-opening the security issue.
Signed-off-by: Samuel Thibault samuel.thibault@ens-lyon.org Fixes: 83efeeeb3d04 ("tty: Allow TIOCSTI to be disabled")
Based on the design of brltty, this appears to be the only solution. I remain surprised that FreeBSD had no brltty support, which is why they didn't run into this problem.
Acked-by: Kees Cook keescook@chromium.org
-Kees
Index: linux-6.4/drivers/tty/tty_io.c
--- linux-6.4.orig/drivers/tty/tty_io.c +++ linux-6.4/drivers/tty/tty_io.c @@ -2276,7 +2276,7 @@ static int tiocsti(struct tty_struct *tt char ch, mbz = 0; struct tty_ldisc *ld;
- if (!tty_legacy_tiocsti)
- if (!tty_legacy_tiocsti && !capable(CAP_SYS_ADMIN)) return -EIO;
if ((current->signal->tty != tty) && !capable(CAP_SYS_ADMIN))
linux-stable-mirror@lists.linaro.org
-
Kees Cook -
kernel test robot -
Samuel Thibault