Date: Sun, 27 Dec 2009 09:03:00 -0600
From: "Serge E. Hallyn" <serge@hallyn.com>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: pavel@ucw.cz, viro@ZenIV.linux.org.uk, michael@laptop.org,
       linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
       linux-security-module@vger.kernel.org, andi@firstfloor.org,
       david@lang.hm, socketcan@hartkopp.net, alan@lxorguk.ukuu.org.uk,
       herbert@gondor.apana.org.au, Valdis.Kletnieks@vt.edu, bdonlan@gmail.com,
       zbr@ioremap.net, cscott@cscott.net, jmorris@namei.org,
       ebiederm@xmission.com, bernie@codewiz.org, mrs@mythic-beasts.com,
       randy.dunlap@oracle.com, xiyou.wangcong@gmail.com, sam@synack.fr,
       casey@schaufler-ca.com, serue@us.ibm.com
Subject: Re: RFC: disablenetwork facility. (v4)
Message-ID: <20091227150300.GB19414@hallyn.com>
References: <20091227010441.GA12077@heat> <200912271736.GDB17180.OFJHOOQStMFLVF@I-love.SAKURA.ne.jp> <20091227083857.GC11737@elf.ucw.cz> <200912272049.FIB35755.OMFFOOJQtVLFSH@I-love.SAKURA.ne.jp>
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Quoting Tetsuo Handa (penguin-kernel@I-love.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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