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Date:   Thu, 18 Jul 2019 12:44:04 -0700
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Subject: [PATCH V36 18/29] Lock down TIOCSSERIAL
From:   Matthew Garrett <matthewgarrett@google.com>
To:     jmorris@namei.org
Cc:     linux-security-module@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
        David Howells <dhowells@redhat.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Matthew Garrett <mjg59@google.com>,
        Kees Cook <keescook@chromium.org>,
        Jiri Slaby <jslaby@suse.com>, linux-serial@vger.kernel.org
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: David Howells <dhowells@redhat.com>

Lock down TIOCSSERIAL as that can be used to change the ioport and irq
settings on a serial port.  This only appears to be an issue for the serial
drivers that use the core serial code.  All other drivers seem to either
ignore attempts to change port/irq or give an error.

Reported-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Matthew Garrett <mjg59@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
cc: Jiri Slaby <jslaby@suse.com>
Cc: linux-serial@vger.kernel.org
---
 drivers/tty/serial/serial_core.c | 5 +++++
 include/linux/security.h         | 1 +
 security/lockdown/lockdown.c     | 1 +
 3 files changed, 7 insertions(+)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 4223cb496764..6e713be1d4e9 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -22,6 +22,7 @@
 #include <linux/serial_core.h>
 #include <linux/delay.h>
 #include <linux/mutex.h>
+#include <linux/security.h>
 
 #include <linux/irq.h>
 #include <linux/uaccess.h>
@@ -862,6 +863,10 @@ static int uart_set_info(struct tty_struct *tty, struct tty_port *port,
 		goto check_and_exit;
 	}
 
+	retval = security_locked_down(LOCKDOWN_TIOCSSERIAL);
+	if (retval && (change_irq || change_port))
+		goto exit;
+
 	/*
 	 * Ask the low level driver to verify the settings.
 	 */
diff --git a/include/linux/security.h b/include/linux/security.h
index 3773ad09b831..8f7048395114 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -112,6 +112,7 @@ enum lockdown_reason {
 	LOCKDOWN_MSR,
 	LOCKDOWN_ACPI_TABLES,
 	LOCKDOWN_PCMCIA_CIS,
+	LOCKDOWN_TIOCSSERIAL,
 	LOCKDOWN_INTEGRITY_MAX,
 	LOCKDOWN_CONFIDENTIALITY_MAX,
 };
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index 22482e1b9a77..00a3a6438dd2 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -27,6 +27,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
 	[LOCKDOWN_MSR] = "raw MSR access",
 	[LOCKDOWN_ACPI_TABLES] = "modifying ACPI tables",
 	[LOCKDOWN_PCMCIA_CIS] = "direct PCMCIA CIS storage",
+	[LOCKDOWN_TIOCSSERIAL] = "reconfiguration of serial port IO",
 	[LOCKDOWN_INTEGRITY_MAX] = "integrity",
 	[LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
 };
-- 
2.22.0.510.g264f2c817a-goog