linux-kernel - Re: Fix sel_netnode_insert suspicious rcu dereference.

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Message-ID: <20120806190930.GH2401@linux.vnet.ibm.com>
Date:	Mon, 6 Aug 2012 12:09:30 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>, eparis@...hat.com,
	paul@...l-moore.com, Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: Fix sel_netnode_insert suspicious rcu dereference.

On Mon, Aug 06, 2012 at 12:49:14PM -0400, Dave Jones wrote:
> On Tue, Jun 05, 2012 at 01:12:39AM -0400, Dave Jones wrote:
>  > I reported this a year ago (https://lkml.org/lkml/2011/4/20/308).
>  > It's still a problem apparently ...
> 
> And another two months pass in silence.
> 
> This is happening to other people too.
> https://bugzilla.redhat.com/show_bug.cgi?id=846037
> 
> Can someone please apply this patch, or at least point out what's wrong with it ?

Feel free to add:

Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

in case that helps.

							Thanx, Paul

> 	Dave
> 
> 
>  > ===============================
>  > [ INFO: suspicious RCU usage. ]
>  > 3.5.0-rc1+ #63 Not tainted
>  > -------------------------------
>  > security/selinux/netnode.c:178 suspicious rcu_dereference_check() usage!
>  > 
>  > other info that might help us debug this:
>  > 
>  > 
>  > rcu_scheduler_active = 1, debug_locks = 0
>  > 1 lock held by trinity-child1/8750:
>  >  #0:  (sel_netnode_lock){+.....}, at: [<ffffffff812d8f8a>] sel_netnode_sid+0x16a/0x3e0
>  > 
>  > stack backtrace:
>  > Pid: 8750, comm: trinity-child1 Not tainted 3.5.0-rc1+ #63
>  > Call Trace:
>  >  [<ffffffff810cec2d>] lockdep_rcu_suspicious+0xfd/0x130
>  >  [<ffffffff812d91d1>] sel_netnode_sid+0x3b1/0x3e0
>  >  [<ffffffff812d8e20>] ? sel_netnode_find+0x1a0/0x1a0
>  >  [<ffffffff812d24a6>] selinux_socket_bind+0xf6/0x2c0
>  >  [<ffffffff810cd1dd>] ? trace_hardirqs_off+0xd/0x10
>  >  [<ffffffff810cdb55>] ? lock_release_holdtime.part.9+0x15/0x1a0
>  >  [<ffffffff81093841>] ? lock_hrtimer_base+0x31/0x60
>  >  [<ffffffff812c9536>] security_socket_bind+0x16/0x20
>  >  [<ffffffff815550ca>] sys_bind+0x7a/0x100
>  >  [<ffffffff816c03d5>] ? sysret_check+0x22/0x5d
>  >  [<ffffffff810d392d>] ? trace_hardirqs_on_caller+0x10d/0x1a0
>  >  [<ffffffff8133b09e>] ? trace_hardirqs_on_thunk+0x3a/0x3f
>  >  [<ffffffff816c03a9>] system_call_fastpath+0x16/0x1b
>  > 
>  > This patch below does what Paul McKenney suggested in the previous thread.
>  > 
>  > Signed-off-by: Dave Jones <davej@...hat.com>
>  > 
>  > diff --git a/security/selinux/netnode.c b/security/selinux/netnode.c
>  > index 28f911c..c5454c0 100644
>  > --- a/security/selinux/netnode.c
>  > +++ b/security/selinux/netnode.c
>  > @@ -174,7 +174,8 @@ static void sel_netnode_insert(struct sel_netnode *node)
>  >  	if (sel_netnode_hash[idx].size == SEL_NETNODE_HASH_BKT_LIMIT) {
>  >  		struct sel_netnode *tail;
>  >  		tail = list_entry(
>  > -			rcu_dereference(sel_netnode_hash[idx].list.prev),
>  > +			rcu_dereference_protected(sel_netnode_hash[idx].list.prev,
>  > +						  lockdep_is_held(&sel_netnode_lock)),
>  >  			struct sel_netnode, list);
>  >  		list_del_rcu(&tail->list);
>  >  		kfree_rcu(tail, rcu);
>  > --
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> ---end quoted text---
> 

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