linux-kernel - [PATCH] Input: analog - fix invalid snprintf() call

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Date:   Tue, 23 Mar 2021 14:14:50 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Zhang Qilong <zhangqilong3@...wei.com>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] Input: analog - fix invalid snprintf() call

From: Arnd Bergmann <arnd@...db.de>

overlapping input and output arguments to snprintf() are
undefined behavior in C99:

drivers/input/joystick/analog.c: In function 'analog_name':
drivers/input/joystick/analog.c:428:3: error: 'snprintf' argument 4 overlaps destination object 'analog' [-Werror=restrict]
  428 |   snprintf(analog->name, sizeof(analog->name), "%s %d-hat",
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  429 |     analog->name, hweight16(analog->mask & ANALOG_HATS_ALL));
      |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/input/joystick/analog.c:420:40: note: destination object referenced by 'restrict'-qualified argument 1 was declared here
  420 | static void analog_name(struct analog *analog)
      |                         ~~~~~~~~~~~~~~~^~~~~~

Change this function to just use the offset it already knows.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 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 f798922a4598..8c9fed3f13e2 100644
--- a/drivers/input/joystick/analog.c
+++ b/drivers/input/joystick/analog.c
@@ -419,14 +419,16 @@ 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 len;
+
+	len = snprintf(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));
+		len += snprintf(analog->name + len, sizeof(analog->name) - len, "%d-hat",
+			 hweight16(analog->mask & ANALOG_HATS_ALL));
 
 	if (analog->mask & ANALOG_HAT_FCS)
 		strlcat(analog->name, " FCS", sizeof(analog->name));
-- 
2.29.2