Where am I? :)

[Giorgos Keramidas]

On 2006-03-04 09:00, Kovesdan Gabor <gabor.kovesdan at t-hosting.hu> wrote:
>Giorgos Keramidas wrote:
>>On 2006-03-04 00:44, Kovesdan Gabor <gabor.kovesdan at t-hosting.hu> wrote:
>>> Hello,
>>> look at this:
>>>
>>> root at server# w
>>> 12:41AM  up 82 days, 10:05, 0 users, load averages: 0.00, 0.00, 0.00
>>> USER             TTY      FROM              LOGIN@  IDLE WHAT
>>> root at server#
>>>
>>> Where am I? :) I don't know exactly how it happened, but I'll
>>> investigate, I have an idea and I'll report if I find out.
>>
>> Some programs may tweak wtmp to `hide' users that are actively logged
>> in.  One program that I know can do this is screen(1).  Hitting ``^A L''
>> here, between successive `w' invocations, I can see this:
>>
>> root at flame:/root# w
>> 2:04AM  up  2:10, 1 user, load averages: 0.07, 0.16, 0.19
>> USER             TTY      FROM              LOGIN@  IDLE WHAT
>> root at flame:/root# w
>> 2:05AM  up  2:11, 2 users, load averages: 0.03, 0.14, 0.17
>> USER             TTY      FROM              LOGIN@  IDLE WHAT
>> root             pts/0    :0:S.0            2:05AM     - w
>> root at flame:/root#
>
> And what do the other logged in users see?

Only what `w' can see too.

> With my method I can completely hide, nobody can see me logged in.

What is your method?  I haven't seen any description of how *you* ended
up not being logged in.  Are you using screen(1) or another program that
tweaks /var/log/wtmp?  Which program?  Have you found out why your login
seems record in wtmp was marked as logged out?

> So I think it might be an opportunity to abusing. I'll send a PR soon,
> I just wanted to know before if somebody already knows about this
> trick.

I don't think this is a bug.  The permissions of ``/var/log/wtmp'' are:

    $ ls -ld /var/log/wtmp
    -rw-r--r--  1 root  wheel  - 8052 Mar  4 16:51 /var/log/wtmp

What a bug about this would report is that set-user-id programs, like
screen(1), can do all sorts of nasty things if abused.  This isn't
exactly a bug, but common knowledge.

- Giorgos