Re: suspicious rcu_dereference_check in security/selinux/netnode.c

From: Eric Paris
Date: Wed Apr 20 2011 - 14:42:15 EST


[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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