linux-kernel - Re: [PATCH] Security: Add prctl(PR_{GET,SET}

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Message-ID: <20091217012540.GA2609@heat>
Date:	Wed, 16 Dec 2009 20:25:40 -0500
From:	Michael Stone <michael@...top.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Michael Stone <michael@...top.org>,
	Ulrich Drepper <drepper@...il.com>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>, David Lang <david@...g.hm>,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Bryan Donlan <bdonlan@...il.com>,
	Evgeniy Polyakov <zbr@...emap.net>,
	"C. Scott Ananian" <cscott@...ott.net>,
	James Morris <jmorris@...ei.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Bernie Innocenti <bernie@...ewiz.org>,
	Mark Seaborn <mrs@...hic-beasts.com>
Subject: Re: [PATCH] Security: Add prctl(PR_{GET,SET}_NETWORK) interface.

Andi Kleen wrote:
> On Wed, Dec 16, 2009 at 10:32:43AM -0500, Michael Stone wrote:
>> Daniel Bernstein has observed [1] that security-conscious userland processes
>> may benefit from the ability to irrevocably remove their ability to create,
>> bind, connect to, or send messages except in the case of previously
>> connected sockets or AF_UNIX filesystem sockets. We provide this facility by
>> implementing support for a new prctl(PR_SET_NETWORK) flag named
>> PR_NETWORK_OFF.
>> 
>> This facility is particularly attractive to security platforms like OLPC
>> Bitfrost [2] and to isolation programs like Rainbow [3] and Plash [4].
> 
> What would stop them from ptracing someone else running under the same
> uid who still has the network access? 

Just like in the (revised from last year) rlimits version, there's a hunk in
the prctl_network semantics patch which disables networking-via-ptrace() like
so:

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 23bd09c..5b38db0 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -151,6 +151,8 @@ int __ptrace_may_access(struct task_struct *task, unsigned int mode)
                dumpable = get_dumpable(task->mm);
        if (!dumpable && !capable(CAP_SYS_PTRACE))
                return -EPERM;
+       if (current->network)
+               return -EPERM;

        return security_ptrace_access_check(task, mode);
  }

More questions?

Regards, and thanks for your interest,

Michael
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