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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Sherry Sun <sherry.sun@nxp.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.9 185/245] tty: serial: fsl_lpuart: fix the potential risk of division or modulo by zero
Date:   Mon, 19 Jul 2021 16:52:07 +0200
Message-Id: <20210719144946.382645003@linuxfoundation.org>
In-Reply-To: <20210719144940.288257948@linuxfoundation.org>
References: <20210719144940.288257948@linuxfoundation.org>
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From: Sherry Sun <sherry.sun@nxp.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@nxp.com>
Link: https://lore.kernel.org/r/20210427021226.27468-1-sherry.sun@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.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 5b6093dc3ff2..a4c1797e30d7 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -1766,6 +1766,9 @@ 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