From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753371AbbCJWl0 (ORCPT ); Tue, 10 Mar 2015 18:41:26 -0400 Received: from 251.110.2.81.in-addr.arpa ([81.2.110.251]:46462 "EHLO lxorguk.ukuu.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751844AbbCJWlX (ORCPT ); Tue, 10 Mar 2015 18:41:23 -0400 Date: Tue, 10 Mar 2015 22:41:00 +0000 From: One Thousand Gnomes To: Jiri Slaby Cc: Raymond Jennings , gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, john_paul.perry@alcatel-lucent.com, stable@vger.kernel.org, Linus Torvalds Subject: Re: [PATCH 1/1] tty: fix up atime/mtime mess, take four Message-ID: <20150310224100.48b1adf6@lxorguk.ukuu.org.uk> In-Reply-To: <54FD6F68.2010708@suse.cz> References: <1425058831-13923-1-git-send-email-jslaby@suse.cz> <1425647774.14441.1.camel@avalar.dragonrealms> <54FD6F68.2010708@suse.cz> Organization: Intel Corporation X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.25; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 09 Mar 2015 11:01:12 +0100 Jiri Slaby wrote: > On 03/06/2015, 02:16 PM, Raymond Jennings wrote: > > On Fri, 2015-02-27 at 18:40 +0100, Jiri Slaby wrote: > >> So check the absolute difference of times and if it large than "8 > >> seconds or so", always update the time. That means we will update > >> immediatelly when changing time. Ergo, CAP_SYS_TIME can foul the > >> check, but it was always that way. > > > > If I may ask, what is supposed to happen normally when you write to a > > tty device? I always thought the tty device was treated just like a > > normal file wrt. timestamps. > > > > Now I see a patch for 8 seconds something. > > Yes, because you do not want to be given any clue when users are typing > passwords. You could intercept the length of the password from the > pauses between key strokes (tty timestamps). On any vaguely idle box I can do the same and in fact probably far better by measuring latencies via rdtsc and continually forcing a dword out of cache in a tight loop. It's a pointless change, second granularities are not useful for most kinds of attack of this nature. Alan