linux-kernel - Re: RFC: disablenetwork facility. (v4)

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Date:	Sun, 27 Dec 2009 09:03:00 -0600
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	pavel@....cz, viro@...IV.linux.org.uk, michael@...top.org,
	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, Valdis.Kletnieks@...edu,
	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, casey@...aufler-ca.com,
	serue@...ibm.com
Subject: Re: RFC: disablenetwork facility. (v4)

Quoting Tetsuo Handa (penguin-kernel@...ove.SAKURA.ne.jp):
> Pavel Machek wrote:
> > Syscalls are very wrong granularity for security system. But easy to
> > implement, see seccomp.
> 
> Quoting from http://en.wikipedia.org/wiki/Seccomp
> > It allows a process to make a one-way transition into a "secure" state where
> > it cannot make any system calls except exit(), read() and write() to
> > already-open file descriptors. 
> 
> I think seccomp() is too much restricted to apply for general applications.
> Most applications will need some other syscalls in addition to exit(), read()
> and write(). Most applications cannot use seccomp().
> 
> What I want to do is similar to seccomp(), but allows userland process to
> forbid some syscalls like execve(), mount(), chroot(), link(), unlink(),
> socket(), bind(), listen() etc. selectively.

The nice thing about the disablenetwork module is that (AFAICS so far)
it actually is safe for an unprivileged user to do.  I can't think of
any setuid-root software which, if started with restricted-network by
an unprivileged user, would become unsafe rather than simply failing (*1).

Adding syscalls becomes much scarier.

-serge

*1 - Michael Stone, without looking back over the patches, do you also
restrict opening netlink sockets?  Should we worry about preventing
an error message from being sent to the audit daemon?
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