linux-kernel - [PATCH 4.2.y-ckt 034/206] serial: 8250_pci: fix divide error bug if baud rate is 0

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Message-Id: <1465507015-23052-35-git-send-email-kamal@canonical.com>
Date:	Thu,  9 Jun 2016 14:14:03 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	David Müller <d.mueller@...oft.ch>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 034/206] serial: 8250_pci: fix divide error bug if baud rate is 0

4.2.8-ckt12 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: =?UTF-8?q?David=20M=C3=BCller?= <d.mueller@...oft.ch>

commit 6f210c18c1c0f016772c8cd51ae12a02bfb9e7ef upstream.

Since commit 21947ba654a6 ("serial: 8250_pci: replace switch-case by
formula"), 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.

Signed-off-by: David Müller <d.mueller@...oft.ch>
Fixes: 21947ba654a6 ("serial: 8250_pci: replace switch-case by formula")
Suggested-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 drivers/tty/serial/8250/8250_pci.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c
index 78aeb11..9850bbf 100644
--- a/drivers/tty/serial/8250/8250_pci.c
+++ b/drivers/tty/serial/8250/8250_pci.c
@@ -1402,6 +1402,9 @@ byt_set_termios(struct uart_port *p, struct ktermios *termios,
 	unsigned long m, n;
 	u32 reg;
 
+	/* Gracefully handle the B0 case: fall back to B9600 */
+	fuart = fuart ? fuart : 9600 * 16;
+
 	/* Get Fuart closer to Fref */
 	fuart *= rounddown_pow_of_two(fref / fuart);
 
-- 
2.7.4