linux-kernel - Re: [PATCH 1/1] tty: fix up atime/mtime mess, take four

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <54FFF842.1010504@suse.cz>
Date:	Wed, 11 Mar 2015 09:09:38 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
CC:	Raymond Jennings <shentino@...il.com>, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org, john_paul.perry@...atel-lucent.com,
	stable@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/1] tty: fix up atime/mtime mess, take four

On 03/10/2015, 11:41 PM, One Thousand Gnomes wrote:
> On Mon, 09 Mar 2015 11:01:12 +0100
> Jiri Slaby <jslaby@...e.cz> 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.

I don't know, I have to study and try this first, before I can take any
action.

> It's a pointless change, second granularities are not useful for most
> kinds of attack of this nature.

Yes, that was actually the whole point of the exercise: move from
current_fs_time() (one nanosecond granularity (for devtmpfs)) to
get_seconds() & 7 (8 seconds).

thanks,
-- 
js
suse labs

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/