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Date:      Tue, 14 Mar 2000 07:25:32 -0800 (PST)
From:      Bhishan Hemrajani <bhishan@cytosine.dhs.org>
To:        Sheldon Hearn <sheldonh@uunet.co.za>
Cc:        freebsd-questions@FreeBSD.ORG
Subject:   Re: DoS attack, Mail errors on new account
Message-ID:  <200003141525.HAA36430@cytosine.dhs.org>
In-Reply-To: <97077.953029254@axl.ops.uunet.co.za> from Sheldon Hearn at "Mar 14, 2000 12:20:54 pm"

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I'm pretty new at freebsd, could you help me with what
you said?

Also, /var/mail is writeable by the group mail, I think:
drwxrwxr-x  2 root    mail          512 Mar 14 07:24 mail

Thank you.

--bhishan

> 
> 
> On Fri, 10 Mar 2000 17:51:47 PST, Bhishan Hemrajani wrote:
> 
> > 1. I have experienced a DoS attack by one of my users
> >    who has used 100% of the cpu.
> 
> I'm not saying it wasn't a DoS attack, but you should be aware that a
> process listed as using 100% CPU isn't always denying service.  If
> nothing else requires much CPU, any relatively CPU-intensive process is
> going to get 100% CPU.
> 
> >    I do have limits, and the
> >    process was killed after consuming 1h of CPU time.
> >    is there any way to limit the process to CPU usage?
> 
> Not in the way I think you want.  It sounds like you want to throttle
> CPU usage, so that a given user or class of users isn't allowed to use
> more than a certain percentage of the available CPU at a given time.
> You can't do that.
> 
> What you _can_ do is add the users to a login class (see the
> login.conf(5) manual page) which has a high "priority".  This is a
> confusing name for the capability; it represents the initial _nice_
> level at which to run processes for these users.  This will be very
> effective in controlling CPU-bound processes, but pretty ineffective
> against controlling IO-bound processes.
> 
> > 2. After I create a user, the mail box doesn't seem to work
> >    correctly. I try to run elm as a new user that I created
> >    and it is exiting with a signal 6 because it cannot read
> >    /var/mail/user.
> > 
> > This is a printout of ll in that dir after that command has run:
> > -r--------  1 test     mail      5 Mar 10 17:36 test.lock
> 
> Hmmm.  What ownerships and permissions to you have on the /var/mail
> directory?  If they're writable by group mail, you can probably make the
> elm binary sgid (2555) to group mail.  That should allow this type of
> mailbox locking.
> 
> Ciao,
> Sheldon.
> 
> 
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