linux-kernel - Re: [PATCH 2/3] Security: Implement disablenetwork semantics. (v4)

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Date:	Mon, 11 Jan 2010 22:19:48 -0500
From:	Valdis.Kletnieks@...edu
To:	Casey Schaufler <casey@...aufler-ca.com>
Cc:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	michael@...top.org, pavel@....cz, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, linux-security-module@...r.kernel.org,
	andi@...stfloor.org, david@...g.hm, socketcan@...tkopp.net,
	alan@...rguk.ukuu.org.uk, herbert@...dor.apana.org.au,
	bdonlan@...il.com, zbr@...emap.net, cscott@...ott.net,
	jmorris@...ei.org, ebiederm@...ssion.com, bernie@...ewiz.org,
	mrs@...hic-beasts.com, randy.dunlap@...cle.com,
	xiyou.wangcong@...il.com, sam@...ack.fr, serue@...ibm.com,
	viro@...IV.linux.org.uk
Subject: Re: [PATCH 2/3] Security: Implement disablenetwork semantics. (v4)

On Sun, 10 Jan 2010 17:46:49 PST, Casey Schaufler said:
> It's much worse than that. A user that has been network disabled
> who tries using ls may find that it goes looking for the network
> on each name lookup and has to wait for a timeout for each.

Ya know Casey - I learned back in 1986 or so that if you set up a SunOS 3.2
cluster using Yellow Pages, professors who managed to unplug the AUI cable
on the back of their Sun 3/50 would notice things blowing chunks.  I have to
admit that 24 years ago I told them "Well don't do that then", and I have
to say the same thing for anybody running a login shell network-disabled.

Now, a more subtle point is that a *program* may call getuserbyname() or
getuserbyuid() and be surprised when it times out - but that's a
different issue than a network-deprived user calling /bin/ls.

>          Then, if there are local file entries that differ
> from the "official" network account values when the library
> functions finally fall back on the local values you get the wrong
> names for file owners.

The sysadmin who set that up already had the bullet in the chamber and
the gun pointed at their feet.  This is another "we knew better a quarter
century ago" issue - SunOS allowed '+:' at the end of /etc/passwd to merge
in the YP database, and Sun actively discouraged the sort of "local userid
overlaps the YP userid space" misconfiguration you mention.

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