tty: wipe buffer.

After we are done with the tty buffer, zero it out.

Reported-by: aszlig <[e-mail]>
Tested-by: Milan Broz <[e-mail]>
Tested-by: Daniel Zatovic <[e-mail]>
Tested-by: aszlig <[e-mail]>
Cc: Willy Tarreau <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/tty_buffer.c

···
 {
 	unsigned char *p = char_buf_ptr(head, head->read);
 	char	      *f = NULL;
+	int n;
 
 	if (~head->flags & TTYB_NORMAL)
 		f = flag_buf_ptr(head, head->read);
 
-	return port->client_ops->receive_buf(port, p, f, count);
+	n = port->client_ops->receive_buf(port, p, f, count);
+	if (n > 0)
+		memset(p, 0, n);
+	return n;
 }
 
 /**