From: Kees Cook <keescook@chromium.org>
To: Samuel Thibault <samuel.thibault@ens-lyon.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Randy Dunlap <rdunlap@infradead.org>,
Jiri Slaby <jirislaby@kernel.org>,
Simon Brand <simon.brand@postadigitale.de>,
stable@vger.kernel.org, linux-kernel@vger.kernel.org,
Dave@mielke.cc
Subject: Re: [PATCH] TIOCSTI: always enable for CAP_SYS_ADMIN
Date: Mon, 3 Jul 2023 12:43:15 -0700 [thread overview]
Message-ID: <202307031241.C7286A7B2@keescook> (raw)
In-Reply-To: <20230701235918.kwfathbdklkyrbde@begin>
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))
--
Kees Cook
next prev parent reply other threads:[~2023-07-03 19:43 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-01 23:59 [PATCH] TIOCSTI: always enable for CAP_SYS_ADMIN Samuel Thibault
2023-07-03 19:43 ` Kees Cook [this message]
-- strict thread matches above, loose matches on Subject: below --
2023-07-10 0:26 Samuel Thibault
2023-07-13 6:01 ` Jiri Slaby
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