Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964826Ab2EOPMg (ORCPT ); Tue, 15 May 2012 11:12:36 -0400 Received: from mail-qa0-f46.google.com ([209.85.216.46]:38790 "EHLO mail-qa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756047Ab2EOPMd (ORCPT ); Tue, 15 May 2012 11:12:33 -0400 From: Paul Moore To: Eric Paris Cc: paulmck@linux.vnet.ibm.com, Dave Jones , sds@tycho.nsa.gov, Linux Kernel Subject: Re: suspicious RCU usage in security/selinux/netnode.c Date: Tue, 15 May 2012 11:12:27 -0400 Message-ID: <1923713.Kphzxkir2y@sifl> User-Agent: KMail/4.8.3 (Linux/3.3.4-gentoo; KDE/4.8.3; x86_64; ; ) In-Reply-To: References: <20120515044145.GA21910@redhat.com> <20120515144658.GC2461@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2456 Lines: 57 On Tuesday, May 15, 2012 10:52:07 AM Eric Paris wrote: > On Tue, May 15, 2012 at 10:46 AM, Paul E. McKenney > > wrote: > > On Tue, May 15, 2012 at 10:24:23AM -0400, Eric Paris wrote: > >> On Tue, May 15, 2012 at 1:16 AM, Paul E. McKenney > >> > >> wrote: > >> > On Tue, May 15, 2012 at 12:41:45AM -0400, Dave Jones wrote: > >> >> I just triggered this on Linus' current tree. > >> > > >> > This is a bare: > >> > > >> > rcu_dereference(sel_netnode_hash[idx].list.prev) > >> > > >> > which needs to be in an RCU read-side critical section. Alternatively, > >> > the above should instead be something like: > >> > > >> > rcu_dereference_check(sel_netnode_hash[idx].list.prev, > >> > lockdep_is_held(&sel_netnode_lock)); > >> > >> Right, but that 'bare' dereference comes from > >> list_for_each_entry_rcu(), [from sel_netnode_sid_slow()] which I don't > >> see how to easily annotate with the lock. Nor do I think it's within > >> my brain power (or my willingness to maintain such in the future) to > >> want to open code that logic. > > > > You lost me on this one. The lockdep splat called out the > > rcu_dereference() above, not a list_for_each_entry_rcu(). Besides which, > > the list_for_each_entry_rcu() does not do the checking -- at the time, > > I was not willing to explode the API that much. > > Ohhhh, ok. I assumed we needed to annotate list_for_each_entry_rcu() > under the spinlock as well as the bare dereference in the insert code. > Ok, should be very easy to fix, although the list running code is > still going to be un-annotated in any way. Thanks Sorry, email filters went awry and I lost this thread until Eric pointed it out to me ... Despite a common first name, the other Paul is the RCU expert, no I unfortunately. Can someone explain the difference between rcu_dereference_check() and rcu_dereference_protected()? We use rcu_dereference_protected() for a very similar reason in selinux/netport.c:sel_netport_insert() and it seems like a better choice ... ? I'll throw a patch together but wanted to clear this up first. -- paul moore www.paul-moore.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/