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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, Igor Pylypiv <igor.pylypiv@gmail.com>,
        Guenter Roeck <linux@roeck-us.net>,
        Wim Van Sebroeck <wim@iguana.be>,
        Sasha Levin <alexander.levin@microsoft.com>
Subject: [PATCH 4.4 123/268] watchdog: f71808e_wdt: Fix magic close handling
Date:   Mon, 28 May 2018 12:01:37 +0200
Message-Id: <20180528100216.042281572@linuxfoundation.org>
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4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Igor Pylypiv <igor.pylypiv@gmail.com>

[ Upstream commit 7bd3e7b743956afbec30fb525bc3c5e22e3d475c ]

Watchdog close is "expected" when any byte is 'V' not just the last one.
Writing "V" to the device fails because the last byte is the end of string.

$ echo V > /dev/watchdog
f71808e_wdt: Unexpected close, not stopping watchdog!

Signed-off-by: Igor Pylypiv <igor.pylypiv@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/watchdog/f71808e_wdt.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/watchdog/f71808e_wdt.c
+++ b/drivers/watchdog/f71808e_wdt.c
@@ -520,7 +520,8 @@ static ssize_t watchdog_write(struct fil
 				char c;
 				if (get_user(c, buf + i))
 					return -EFAULT;
-				expect_close = (c == 'V');
+				if (c == 'V')
+					expect_close = true;
 			}
 
 			/* Properly order writes across fork()ed processes */