Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Mon, 10 Jul 2023 02:26:45 +0200
From:   Samuel Thibault <samuel.thibault@ens-lyon.org>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        Simon Brand <simon.brand@postadigitale.de>,
        Kees Cook <keescook@chromium.org>
Cc:     linux-kernel@vger.kernel.org, Dave@mielke.cc
Subject: [PATCH] TIOCSTI: always enable for CAP_SYS_ADMIN
Message-ID: <20230710002645.v565c7xq5iddruse@begin>
Mail-Followup-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>,
        Kees Cook <keescook@chromium.org>, linux-kernel@vger.kernel.org,
        Dave@mielke.cc
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
User-Agent: NeoMutt/20170609 (1.8.3)
Precedence: bulk

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>
Acked-by: Kees Cook <keescook@chromium.org>
Fixes: 83efeeeb3d04 ("tty: Allow TIOCSTI to be disabled")
Cc: stable@vger.kernel.org

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))