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Date:      Sat, 01 Dec 2001 08:20:01 -0600
From:      scott <scott@bsdprophet.org>
To:        Dave <mudman@R181172.resnet.ucsb.edu>
Cc:        freebsd-security@FreeBSD.ORG
Subject:   Re: options USER_LDT
Message-ID:  <3C08E711.A4B08098@bsdprophet.org>
References:  <Pine.BSF.4.33.0111302322520.763-100000@R181172.resnet.ucsb.edu>

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Dave wrote:
> 
> I really have no clue what the kernel option:
> options USER_LDT
> 
> means, except this rugged definition I found in LINT (paraphrase):
> "Allow applications running in user space to manipulate the Local
> Descriptor Table (LDT)"
> 
> Since it didn't come in the GENERIC (FBSD 4.4 REL), I'm assuming that
> someone, somewhere, thought it would be a good idea to have this disabled
> by default and maybe it was meant to be added in only by people who know
> what they are doing.
> 
> Is there a security risk by allowing programs to access the Local
> Descriptor Table?  (I'm not sure what the LDT is, but if it was off for a
> reason I wouldn't want to challenge the decisions of those more informed
> than myself.  If it wasn't for an efficiency judgement, it could of been
> for a security judgement)

Yes there is a security risk.
Here read all about it:
http://www.phrack.org/show.php?p=51&a=9

> 
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-- 
Scott

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