[PATCH V31 17/25] 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, dhowells@redhat.com,
	linux-api@vger.kernel.org, luto@kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Matthew Garrett <mjg59@google.com>, Jiri Slaby <jslaby@suse.com>,
	linux-serial@vger.kernel.org
Subject: [PATCH V31 17/25] Lock down TIOCSSERIAL
Date: Tue, 26 Mar 2019 11:27:33 -0700	[thread overview]
Message-ID: <20190326182742.16950-18-matthewgarrett@google.com> (raw)
In-Reply-To: <20190326182742.16950-1-matthewgarrett@google.com>

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>
cc: Jiri Slaby <jslaby@suse.com>
Cc: linux-serial@vger.kernel.org
---
 drivers/tty/serial/serial_core.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index d4cca5bdaf1c..65b67f0d4386 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -842,6 +842,12 @@ static int uart_set_info(struct tty_struct *tty, struct tty_port *port,
 	new_flags = (__force upf_t)new_info->flags;
 	old_custom_divisor = uport->custom_divisor;
 
+	if ((change_port || change_irq) &&
+	    kernel_is_locked_down("Using TIOCSSERIAL to change device addresses, irqs and dma channels", LOCKDOWN_INTEGRITY)) {
+		retval = -EPERM;
+		goto exit;
+	}
+
 	if (!capable(CAP_SYS_ADMIN)) {
 		retval = -EPERM;
 		if (change_irq || change_port ||
-- 
2.21.0.392.gf8f6787159e-goog

