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

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Message-Id: <20221129141819.15310-1-johan@kernel.org>
Date:   Tue, 29 Nov 2022 15:18:19 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Ji-Ze Hong <hpeter@...il.com>
Subject: [PATCH] USB: serial: f81534: fix division by zero on line-speed change

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@...r.kernel.org      # 4.16
Cc: Ji-Ze Hong (Peter Hong) <hpeter@...il.com>
Signed-off-by: Johan Hovold <johan@...nel.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