tty/vt: consolemap: walk the buffer only once in con_set_trans_old()

Fetch the user data one by one (by get_user()) and fill in the local
buffer simultaneously. I.e. we no longer require to walk two buffers and
save thus 256 B from stack (whole ubuf).
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220607104946.18710-36-jslaby@suse.czSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/vt/consolemap.c

@@ -343,15 +343,15 @@ static void update_user_maps(void)
  */
 int con_set_trans_old(unsigned char __user * arg)
 {
-	int i;
 	unsigned short inbuf[E_TABSZ];
-	unsigned char ubuf[E_TABSZ];
-
-	if (copy_from_user(ubuf, arg, E_TABSZ))
-		return -EFAULT;
+	unsigned int i;
+	unsigned char ch;
 
-	for (i = 0; i < E_TABSZ ; i++)
-		inbuf[i] = UNI_DIRECT_BASE | ubuf[i];
+	for (i = 0; i < ARRAY_SIZE(inbuf); i++) {
+		if (get_user(ch, &arg[i]))
+			return -EFAULT;
+		inbuf[i] = UNI_DIRECT_BASE | ch;
+	}
 
 	console_lock();
 	memcpy(translations[USER_MAP], inbuf, sizeof(inbuf));