[PATCH V31 17/25] Lock down TIOCSSERIAL

Matthew Garrett matthewgarrett at google.com
Tue Mar 26 18:27:33 UTC 2019

From: David Howells <dhowells at 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 at linuxfoundation.org>
Signed-off-by: David Howells <dhowells at redhat.com>
Signed-off-by: Matthew Garrett <mjg59 at google.com>
cc: Jiri Slaby <jslaby at suse.com>
Cc: linux-serial at 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 ||

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