[PATCH 19/27] Lock down TIOCSSERIAL

From: Matthew Garrett
Date: Thu Feb 28 2019 - 18:13:49 EST


From: David Howells <dhowells@xxxxxxxxxx>

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@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Jiri Slaby <jslaby@xxxxxxxx>
---
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 556f50aa1b58..627e859ae25a 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -852,6 +852,12 @@ 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")) {
+ retval = -EPERM;
+ goto exit;
+ }
+
if (!capable(CAP_SYS_ADMIN)) {
retval = -EPERM;
if (change_irq || change_port ||
--
2.21.0.352.gf09ad66450-goog