[PATCH] USB: serial: f81534: fix division by zero on line-speed change

[PATCH] USB: serial: f81534: fix division by zero on line-speed change

[Johan Hovold]

The driver leaves the line speed unchanged in case a requested speed is
not supported. Make sure to handle the case where the current speed is
B0 (hangup) without dividing by zero when determining the clock source.

Fixes: 3aacac02f385 ("USB: serial: f81534: add high baud rate support")
Cc: stable@vger.kernel.org      # 4.16
Cc: Ji-Ze Hong (Peter Hong) <hpeter@gmail.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/usb/serial/f81534.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/serial/f81534.c b/drivers/usb/serial/f81534.c
index ddfcd72eb0ae..4083ae961be4 100644
--- a/drivers/usb/serial/f81534.c
+++ b/drivers/usb/serial/f81534.c
@@ -536,9 +536,6 @@ static int f81534_submit_writer(struct usb_serial_port *port, gfp_t mem_flags)
 
 static u32 f81534_calc_baud_divisor(u32 baudrate, u32 clockrate)
 {
-	if (!baudrate)
-		return 0;
-
 	/* Round to nearest divisor */
 	return DIV_ROUND_CLOSEST(clockrate, baudrate);
 }
@@ -568,9 +565,14 @@ static int f81534_set_port_config(struct usb_serial_port *port,
 	u32 baud_list[] = {baudrate, old_baudrate, F81534_DEFAULT_BAUD_RATE};
 
 	for (i = 0; i < ARRAY_SIZE(baud_list); ++i) {
-		idx = f81534_find_clk(baud_list[i]);
+		baudrate = baud_list[i];
+		if (baudrate == 0) {
+			tty_encode_baud_rate(tty, 0, 0);
+			return 0;
+		}
+
+		idx = f81534_find_clk(baudrate);
 		if (idx >= 0) {
-			baudrate = baud_list[i];
 			tty_encode_baud_rate(tty, baudrate, baudrate);
 			break;
 		}
-- 
2.37.4

Re: [PATCH] USB: serial: f81534: fix division by zero on line-speed change

[Greg KH]

On Tue, Nov 29, 2022 at 03:18:19PM +0100, Johan Hovold wrote:
> The driver leaves the line speed unchanged in case a requested speed is
> not supported. Make sure to handle the case where the current speed is
> B0 (hangup) without dividing by zero when determining the clock source.
> 
> Fixes: 3aacac02f385 ("USB: serial: f81534: add high baud rate support")
> Cc: stable@vger.kernel.org      # 4.16
> Cc: Ji-Ze Hong (Peter Hong) <hpeter@gmail.com>
> Signed-off-by: Johan Hovold <johan@kernel.org>

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>