lwtunnel: Fix oops on state free after encap module unload

[ Upstream commit 85c81401 ]

When attempting to free lwtunnel state after the module for the encap
has been unloaded an oops occurs:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
IP: lwtstate_free+0x18/0x40
[..]
task: ffff88003e372380 task.stack: ffffc900001fc000
RIP: 0010:lwtstate_free+0x18/0x40
RSP: 0018:ffff88003fd83e88 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff88002bbb3380 RCX: ffff88000c91a300
[..]
Call Trace:
 <IRQ>
 free_fib_info_rcu+0x195/0x1a0
 ? rt_fibinfo_free+0x50/0x50
 rcu_process_callbacks+0x2d3/0x850
 ? rcu_process_callbacks+0x296/0x850
 __do_softirq+0xe4/0x4cb
 irq_exit+0xb0/0xc0
 smp_apic_timer_interrupt+0x3d/0x50
 apic_timer_interrupt+0x93/0xa0
[..]
Code: e8 6e c6 fc ff 89 d8 5b 5d c3 bb de ff ff ff eb f4 66 90 66 66 66 66 90 55 48 89 e5 53 0f b7 07 48 89 fb 48 8b 04 c5 00 81 d5 81 <48> 8b 40 08 48 85 c0 74 13 ff d0 48 8d 7b 20 be 20 00 00 00 e8

The problem is after the module for the encap can be unloaded the
corresponding ops is removed and is thus NULL here.

Modules implementing lwtunnel ops should not be allowed to unload
while there is state alive using those ops, so grab the module
reference for the ops on creating lwtunnel state and of course release
the reference when freeing the state.

Fixes: 1104d9ba ("lwtunnel: Add destroy state operation")
Signed-off-by: Robert Shearman <rshearma@brocade.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/net/lwtunnel.h

@@ -48,10 +48,7 @@ struct lwtunnel_encap_ops {
 };
 
 #ifdef CONFIG_LWTUNNEL
-static inline void lwtstate_free(struct lwtunnel_state *lws)
-{
-	kfree(lws);
-}
+void lwtstate_free(struct lwtunnel_state *lws);
 
 static inline struct lwtunnel_state *
 lwtstate_get(struct lwtunnel_state *lws)

net/core/lwtunnel.c

@@ -66,6 +66,15 @@ EXPORT_SYMBOL(lwtunnel_state_alloc);
 static const struct lwtunnel_encap_ops __rcu *
 		lwtun_encaps[LWTUNNEL_ENCAP_MAX + 1] __read_mostly;
 
+void lwtstate_free(struct lwtunnel_state *lws)
+{
+	const struct lwtunnel_encap_ops *ops = lwtun_encaps[lws->type];
+
+	kfree(lws);
+	module_put(ops->owner);
+}
+EXPORT_SYMBOL(lwtstate_free);
+
 int lwtunnel_encap_add_ops(const struct lwtunnel_encap_ops *ops,
 			   unsigned int num)
 {
@@ -111,8 +120,11 @@ int lwtunnel_build_state(struct net_device *dev, u16 encap_type,
 	ret = -EOPNOTSUPP;
 	rcu_read_lock();
 	ops = rcu_dereference(lwtun_encaps[encap_type]);
-	if (likely(ops && ops->build_state))
+	if (likely(ops && ops->build_state && try_module_get(ops->owner))) {
 		ret = ops->build_state(dev, encap, family, cfg, lws);
+		if (ret)
+			module_put(ops->owner);
+	}
 	rcu_read_unlock();
 
 	return ret;