linux-kernel - [PATCH 4.4 039/118] serial: 8250_mid: fix divide error bug if baud rate is 0

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Date:   Thu, 22 Sep 2016 19:28:59 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Mendez Salinas, Fernando" <fernando.mendez.salinas@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: [PATCH 4.4 039/118] serial: 8250_mid: fix divide error bug if baud rate is 0

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

commit 47b34d2ef266e2c283b514d65c8963c2ccd42474 upstream.

Since the commit c1a67b48f6a5 ("serial: 8250_pci: replace switch-case by
formula for Intel MID"), the 8250 driver crashes in the byt_set_termios()
function with a divide error. This is caused by the fact that a baud rate of 0
(B0) is not handled properly. Fix it by falling back to B9600 in this case.

Reported-by: "Mendez Salinas, Fernando" <fernando.mendez.salinas@...el.com>
Fixes: c1a67b48f6a5 ("serial: 8250_pci: replace switch-case by formula for Intel MID")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/tty/serial/8250/8250_mid.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/tty/serial/8250/8250_mid.c
+++ b/drivers/tty/serial/8250/8250_mid.c
@@ -149,6 +149,9 @@ static void mid8250_set_termios(struct u
 	unsigned long w = BIT(24) - 1;
 	unsigned long mul, div;
 
+	/* Gracefully handle the B0 case: fall back to B9600 */
+	fuart = fuart ? fuart : 9600 * 16;
+
 	if (mid->board->freq < fuart) {
 		/* Find prescaler value that satisfies Fuart < Fref */
 		if (mid->board->freq > baud)