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Re: possible security flaw in screen 3.9.5-9



On Sat, Sep 09, 2000 at 12:00:19AM +1100, CaT wrote:
> After installing this utility (which has to be amongst my very
> favourite) I noticed something interesting int he way it behaves.
> Basically, screen does what I first thought of when compiling it
> for myself, which is to put its pipes in /var/run/screen.
> 
> What screen does there is to create subdirs which are then used
> to hold a users pipes. Now these subdirs are owned by the user
> that runs screen. The hassle with this is that it gives the user
> a. a possible way around quotas set on /home b. a method of fully
> filling up /var, thereby potentially causing log entries to be
> lost which, in turn, gives the user anice, untracable way of then
> doing naughty things without those naughty things getting logged.
> Said user can then rm the large file they created and noone would
> be any the wiser.

users have write permission to /var unless you really make alot of
changes, on my system i have:

/var/lock
/var/tmp ## for me this is a sep partition
/var/lib/texmf/*
/var/mail/user

if your worried about users messing with /var put quotas on /var. 

> As such I reckon it's best if the screen directory is left in
> /tmp where the authors initially put it. It's inconvenient but
> doesn't cause the problems above.

more headaches for /tmp cleaners and it does not solve any of the
above problems.  to solve the above problems enforce quotas on /var
(which can be much smaller then /home quotas, say 5 or 10 MB) that is
what i do.

-- 
Ethan Benson
http://www.alaska.net/~erbenson/

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