[PATCH 6.4 158/239] TIOCSTI: always enable for CAP_SYS_ADMIN

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From: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>

commit 690c8b804ad2eafbd35da5d3c95ad325ca7d5061 upstream.

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@xxxxxxxxxxxx>
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
Fixes: 83efeeeb3d04 ("tty: Allow TIOCSTI to be disabled")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Nicolas Pitre <nico@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230710002645.v565c7xq5iddruse@begin
Acked-by: Jiri Slaby <jirislaby@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/tty/tty_io.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/tty/tty_io.c
+++ b/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))





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