[PATCH 1/1] USB: serial: io_ti: fix div-by-zero in set_termios

[Tyler Hicks]

From: Johan Hovold <johan at kernel.org>

Fix a division-by-zero in set_termios when debugging is enabled and a
high-enough speed has been requested so that the divisor value becomes
zero.

Instead of just fixing the offending debug statement, cap the baud rate
at the base as a zero divisor value also appears to crash the firmware.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable <stable at vger.kernel.org>     # 2.6.12
Reviewed-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Johan Hovold <johan at kernel.org>

CVE-2017-18360

(cherry picked from commit 6aeb75e6adfaed16e58780309613a578fe1ee90b)
Signed-off-by: Tyler Hicks <tyhicks at canonical.com>
---
 drivers/usb/serial/io_ti.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/serial/io_ti.c b/drivers/usb/serial/io_ti.c
index 8c2b58ace70a..cbc1b3afca01 100644
--- a/drivers/usb/serial/io_ti.c
+++ b/drivers/usb/serial/io_ti.c
@@ -2233,8 +2233,11 @@ static void change_port_settings(struct tty_struct *tty,
 	if (!baud) {
 		/* pick a default, any default... */
 		baud = 9600;
-	} else
+	} else {
+		/* Avoid a zero divisor. */
+		baud = min(baud, 461550);
 		tty_encode_baud_rate(tty, baud, baud);
+	}
 
 	edge_port->baud_rate = baud;
 	config->wBaudRate = (__u16)((461550L + baud/2) / baud);
-- 
2.7.4