linux-kernel - [PATCH 4.4 143/188] tty: serial: fsl_lpuart: fix the potential risk of division or modulo by zero

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Message-Id: <20210719144941.170298786@linuxfoundation.org>
Date:   Mon, 19 Jul 2021 16:52:07 +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, Sherry Sun <sherry.sun@....com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.4 143/188] tty: serial: fsl_lpuart: fix the potential risk of division or modulo by zero

From: Sherry Sun <sherry.sun@....com>

[ Upstream commit fcb10ee27fb91b25b68d7745db9817ecea9f1038 ]

We should be very careful about the register values that will be used
for division or modulo operations, althrough the possibility that the
UARTBAUD register value is zero is very low, but we had better to deal
with the "bad data" of hardware in advance to avoid division or modulo
by zero leading to undefined kernel behavior.

Signed-off-by: Sherry Sun <sherry.sun@....com>
Link: https://lore.kernel.org/r/20210427021226.27468-1-sherry.sun@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/tty/serial/fsl_lpuart.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 1544a7cc76ff..1319f3dd5b70 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -1681,6 +1681,9 @@ lpuart32_console_get_options(struct lpuart_port *sport, int *baud,
 
 	bd = lpuart32_read(sport->port.membase + UARTBAUD);
 	bd &= UARTBAUD_SBR_MASK;
+	if (!bd)
+		return;
+
 	sbr = bd;
 	uartclk = clk_get_rate(sport->clk);
 	/*
-- 
2.30.2