linux-kernel - [RFC PATCH 7/7] drivers: hwmon: add runtime format string checking

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Message-Id: <20181026232409.16100-8-linux@rasmusvillemoes.dk>
Date:   Sat, 27 Oct 2018 01:24:09 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>
Cc:     linux-kernel@...r.kernel.org,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-hwmon@...r.kernel.org
Subject: [RFC PATCH 7/7] drivers: hwmon: add runtime format string checking

With -Wformat-nonliteral, gcc complains

drivers/hwmon/hwmon.c: In function ‘hwmon_genattr’:
drivers/hwmon/hwmon.c:282:6: warning: format not a string literal, argument types not checked [-Wformat-nonliteral]
      index + hwmon_attr_base(type));

Add a runtime check to ensure that the template indeed has a single %d
printf specifier. Using fmtcheck() also makes gcc verify that the
expression 'index + hwmon_attr_base(type)' is suitable for %d.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 drivers/hwmon/hwmon.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/hwmon/hwmon.c b/drivers/hwmon/hwmon.c
index 33d51281272b..ec6f5f36b5fc 100644
--- a/drivers/hwmon/hwmon.c
+++ b/drivers/hwmon/hwmon.c
@@ -278,7 +278,8 @@ static struct attribute *hwmon_genattr(struct device *dev,
 	if (type == hwmon_chip) {
 		name = (char *)template;
 	} else {
-		scnprintf(hattr->name, sizeof(hattr->name), template,
+		scnprintf(hattr->name, sizeof(hattr->name),
+			  fmtcheck(template, "type%dwhat", 0),
 			  index + hwmon_attr_base(type));
 		name = hattr->name;
 	}
-- 
2.19.1.6.gbde171bbf5