lwtunnel: Fix oops on state free after encap module unload

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: 1104d9ba443a ("lwtunnel: Add destroy state operation")
Signed-off-by: Robert Shearman <rshearma@brocade.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/lwtunnel.c b/net/core/lwtunnel.c
index 47b1dd65947bd2547cf22a0bb84592fef8f28be0..c23465005f2f4ced93d7bcb2754fb267c2cf00d0 100644 (file)
--- a/net/core/lwtunnel.c
+++ b/net/core/lwtunnel.c
@@ -115,8 +115,11 @@ 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;
@@ -194,6 +197,7 @@ void lwtstate_free(struct lwtunnel_state *lws)
        } else {
                kfree(lws);
        }
+       module_put(ops->owner);
 }
 EXPORT_SYMBOL(lwtstate_free);