linux-kernel - [PATCH 3/4] restrict unprivileged TIOCSTI tty ioctl

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Message-Id: <20170417060706.28674-4-matt@nmatt.com>
Date:   Mon, 17 Apr 2017 02:07:05 -0400
From:   Matt Brown <matt@...tt.com>
To:     jmorris@...ei.org, gregkh@...uxfoundation.org,
        akpm@...ux-foundation.org
Cc:     linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
        Matt Brown <matt@...tt.com>
Subject: [PATCH 3/4] restrict unprivileged TIOCSTI tty ioctl

this patch depends on patch 1 and 2

enforces restrictions on unprivileged users injecting commands
into other processes in the same tty session using the TIOCSTI ioctl

Signed-off-by: Matt Brown <matt@...tt.com>
---
 drivers/tty/tty_io.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index e6d1a65..31894e8 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2296,11 +2296,15 @@ static int tty_fasync(int fd, struct file *filp, int on)
  *	FIXME: may race normal receive processing
  */
 
+int tiocsti_restrict = IS_ENABLED(CONFIG_SECURITY_TIOCSTI_RESTRICT);
+
 static int tiocsti(struct tty_struct *tty, char __user *p)
 {
 	char ch, mbz = 0;
 	struct tty_ldisc *ld;
 
+	if (tiocsti_restrict && !capable(CAP_SYS_ADMIN))
+		return -EPERM;
 	if ((current->signal->tty != tty) && !capable(CAP_SYS_ADMIN))
 		return -EPERM;
 	if (get_user(ch, p))
-- 
2.10.2