suspicious rcu_dereference_check in security/selinux/netnode.c

[Dave Jones <davej@redhat.com>]

 ===================================================
 [ 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