linux-kernel - [RFC 2/7] Input: joystick - avoid fragile snprintf use

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Date:	Tue,  8 Mar 2016 21:40:49 +0100
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Kees Cook <keescook@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC 2/7] Input: joystick - avoid fragile snprintf use

Passing overlapping src and dst buffers to snprintf is fragile, and
while it currently works for the special case of passing dst as the
argument corresponding to an initial "%s" in the format string, any
other use would very likely lead to chaos. It's easy enough to avoid,
so let's do that.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 drivers/input/joystick/analog.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/input/joystick/analog.c b/drivers/input/joystick/analog.c
index 6f8b084e13d0..d0a9b90e8f94 100644
--- a/drivers/input/joystick/analog.c
+++ b/drivers/input/joystick/analog.c
@@ -435,14 +435,16 @@ static void analog_calibrate_timer(struct analog_port *port)
 
 static void analog_name(struct analog *analog)
 {
-	snprintf(analog->name, sizeof(analog->name), "Analog %d-axis %d-button",
+	int ret = 0;
+
+	ret = scnprintf(analog->name, sizeof(analog->name), "Analog %d-axis %d-button",
 		 hweight8(analog->mask & ANALOG_AXES_STD),
 		 hweight8(analog->mask & ANALOG_BTNS_STD) + !!(analog->mask & ANALOG_BTNS_CHF) * 2 +
 		 hweight16(analog->mask & ANALOG_BTNS_GAMEPAD) + !!(analog->mask & ANALOG_HBTN_CHF) * 4);
 
 	if (analog->mask & ANALOG_HATS_ALL)
-		snprintf(analog->name, sizeof(analog->name), "%s %d-hat",
-			 analog->name, hweight16(analog->mask & ANALOG_HATS_ALL));
+		scnprintf(analog->name + ret, sizeof(analog->name) - ret, " %d-hat",
+			  hweight16(analog->mask & ANALOG_HATS_ALL));
 
 	if (analog->mask & ANALOG_HAT_FCS)
 		strlcat(analog->name, " FCS", sizeof(analog->name));
-- 
2.1.4