[PATCH] [RESEND] [v2] Input: analog - fix invalid snprintf() call

[Arnd Bergmann]

From: Arnd Bergmann <arnd@xxxxxxxx>

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 use the simpler seq_buf interface instead.

Cc: Rasmus Villemoes <rasmus.villemoes@xxxxxxxxx>
Link: https://lore.kernel.org/all/20210323131456.2600132-1-arnd@xxxxxxxxxx/
Link: https://lore.kernel.org/all/20210324131959.2089129-1-arnd@xxxxxxxxxx/
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
v2: use seq_buf instead of rolling my own

Resending as the second submission somehow got dropped
---
 drivers/input/joystick/analog.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/drivers/input/joystick/analog.c b/drivers/input/joystick/analog.c
index 882c3c8ba399..3c17bf202af5 100644
--- a/drivers/input/joystick/analog.c
+++ b/drivers/input/joystick/analog.c
@@ -19,6 +19,7 @@
 #include <linux/input.h>
 #include <linux/gameport.h>
 #include <linux/jiffies.h>
+#include <linux/seq_buf.h>
 #include <linux/timex.h>
 #include <linux/timekeeping.h>
 
@@ -338,23 +339,24 @@ 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",
+	struct seq_buf s;
+
+	seq_buf_init(&s, analog->name, sizeof(analog->name));
+	seq_buf_printf(&s, "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));
+		seq_buf_printf(&s, " %d-hat",
+			       hweight16(analog->mask & ANALOG_HATS_ALL));
 
 	if (analog->mask & ANALOG_HAT_FCS)
-		strlcat(analog->name, " FCS", sizeof(analog->name));
+		seq_buf_printf(&s, " FCS");
 	if (analog->mask & ANALOG_ANY_CHF)
-		strlcat(analog->name, (analog->mask & ANALOG_SAITEK) ? " Saitek" : " CHF",
-			sizeof(analog->name));
+		seq_buf_printf(&s, (analog->mask & ANALOG_SAITEK) ? " Saitek" : " CHF");
 
-	strlcat(analog->name, (analog->mask & ANALOG_GAMEPAD) ? " gamepad": " joystick",
-		sizeof(analog->name));
+	seq_buf_printf(&s, (analog->mask & ANALOG_GAMEPAD) ? " gamepad": " joystick");
 }
 
 /*
-- 
2.29.2