arch: s390: appldata: using strncpy() and strnlen() instead of sprintf()

'buf[2]' is 2 bytes length, and sprintf() will append '\0' at the end
of string "?\n", so original implementation is memory overflow.

Need use strncpy() and strnlen() instead of sprintf().
Signed-off-by: Chen Gang <gang.chen@asianux.com>
Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/appldata/appldata_base.c

@@ -212,7 +212,9 @@ appldata_timer_handler(ctl_table *ctl, int write,
 		return 0;
 	}
 	if (!write) {
-		len = sprintf(buf, appldata_timer_active ? "1\n" : "0\n");
+		strncpy(buf, appldata_timer_active ? "1\n" : "0\n",
+			ARRAY_SIZE(buf));
+		len = strnlen(buf, ARRAY_SIZE(buf));
 		if (len > *lenp)
 			len = *lenp;
 		if (copy_to_user(buffer, buf, len))
@@ -317,7 +319,8 @@ appldata_generic_handler(ctl_table *ctl, int write,
 		return 0;
 	}
 	if (!write) {
-		len = sprintf(buf, ops->active ? "1\n" : "0\n");
+		strncpy(buf, ops->active ? "1\n" : "0\n", ARRAY_SIZE(buf));
+		len = strnlen(buf, ARRAY_SIZE(buf));
 		if (len > *lenp)
 			len = *lenp;
 		if (copy_to_user(buffer, buf, len)) {