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Subject: Re: suspicious rcu_dereference_check in security/selinux/netnode.c
From: Eric Paris <eparis@redhat.com>
To: Dave Jones <davej@redhat.com>
Cc: sds@tycho.nsa.gov, jmorris@namei.org, eparis@parisplace.org,
        Linux Kernel <linux-kernel@vger.kernel.org>, paul.moore@hp.com,
        selinux@tycho.nsa.gov
In-Reply-To: <20110420183543.GA11965@redhat.com>
References: <20110420183543.GA11965@redhat.com>
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Date: Wed, 20 Apr 2011 14:42:04 -0400
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[added paul] EOM

On Wed, 2011-04-20 at 14:35 -0400, Dave Jones wrote:
> ===================================================
>  [ INFO: suspicious rcu_dereference_check() usage. ]
>  ---------------------------------------------------
>  security/selinux/netnode.c:193 invoked rcu_dereference_check() without protection!
>  
>  other info that might help us debug this:
>  
>  rcu_scheduler_active = 1, debug_locks = 0
>  1 lock held by a.out/2018:
>   #0:  (sel_netnode_lock){+.....}, at: [<ffffffff81212ab7>] sel_netnode_sid+0x9e/0x267
>  
>  stack backtrace:
>  Pid: 2018, comm: a.out Not tainted 2.6.39-rc4+ #3
>  Call Trace:
>   [<ffffffff81084908>] lockdep_rcu_dereference+0xa8/0xb0
>   [<ffffffff81212c0d>] sel_netnode_sid+0x1f4/0x267
>   [<ffffffff81212a19>] ? sel_netnode_find+0xe3/0xe3
>   [<ffffffff8120d564>] selinux_socket_bind+0x1cf/0x26f
>   [<ffffffff81086c08>] ? lock_release+0x181/0x18e
>   [<ffffffff81100db8>] ? might_fault+0xa5/0xac
>   [<ffffffff81100d6f>] ? might_fault+0x5c/0xac
>   [<ffffffff812073f1>] security_socket_bind+0x16/0x18
>   [<ffffffff813ee0e9>] sys_bind+0x73/0xcf
>   [<ffffffff814c5d7a>] ? sysret_check+0x2e/0x69
>   [<ffffffff810870cf>] ? trace_hardirqs_on_caller+0x10b/0x12f
>   [<ffffffff810a9efb>] ? audit_syscall_entry+0x11c/0x148
>   [<ffffffff81255e2e>] ? trace_hardirqs_on_thunk+0x3a/0x3f
>   [<ffffffff814c5d42>] system_call_fastpath+0x16/0x1b
> 
> 
> something like this perhaps ?
> 
> 	Dave
> 
> diff --git a/security/selinux/netnode.c b/security/selinux/netnode.c
> index 65ebfe9..d0c38ba 100644
> --- a/security/selinux/netnode.c
> +++ b/security/selinux/netnode.c
> @@ -188,9 +188,11 @@ static void sel_netnode_insert(struct sel_netnode *node)
>  	list_add_rcu(&node->list, &sel_netnode_hash[idx].list);
>  	if (sel_netnode_hash[idx].size == SEL_NETNODE_HASH_BKT_LIMIT) {
>  		struct sel_netnode *tail;
> +		rcu_read_lock();
>  		tail = list_entry(
>  			rcu_dereference(sel_netnode_hash[idx].list.prev),
>  			struct sel_netnode, list);
> +		rcu_read_unlock();
>  		list_del_rcu(&tail->list);
>  		call_rcu(&tail->rcu, sel_netnode_free);
>  	} else


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