tty: wipe buffer.

commit c9a8e5fc upstream.

After we are done with the tty buffer, zero it out.
Reported-by: aszlig <aszlig@nix.build>
Tested-by: Milan Broz <gmazyland@gmail.com>
Tested-by: Daniel Zatovic <daniel.zatovic@gmail.com>
Tested-by: aszlig <aszlig@nix.build>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_buffer.c

@@ -458,6 +458,8 @@ int tty_ldisc_receive_buf(struct tty_ldisc *ld, unsigned char *p,
 		if (count && ld->ops->receive_buf)
 			ld->ops->receive_buf(ld->tty, p, f, count);
 	}
+	if (count > 0)
+		memset(p, 0, count);
 	return count;
 }
 EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);