There are two pointers in struct xfrm_state_offload, *dev, *real_dev.
These are used in callback functions of struct xfrmdev_ops.
The *dev points whether bonding interface or real interface.
If bonding ipsec offload is used, it points bonding interface If not,
it points real interface.
And real_dev always points real interface.
So, netdevsim should always use real_dev instead of dev.
Of course, real_dev always not be null.

Test commands:
    ip netns add A
    ip netns exec A bash
    modprobe netdevsim
    echo "1 1" > /sys/bus/netdevsim/new_device
    ip link add bond0 type bond mode active-backup
    ip link set eth0 master bond0
    ip link set eth0 up
    ip link set bond0 up
    ip x s add proto esp dst 14.1.1.1 src 15.1.1.1 spi 0x07 mode \
transport reqid 0x07 replay-window 32 aead 'rfc4106(gcm(aes))' \
0x44434241343332312423222114131211f4f3f2f1 128 sel src 14.0.0.52/24 \
dst 14.0.0.70/24 proto tcp offload dev bond0 dir in

Splat looks like:
BUG: spinlock bad magic on CPU#5, kworker/5:1/53
 lock: 0xffff8881068c2cc8, .magic: 11121314, .owner: <none>/-1,
.owner_cpu: -235736076
CPU: 5 PID: 53 Comm: kworker/5:1 Not tainted 5.13.0-rc3+ #1168
Workqueue: events linkwatch_event
Call Trace:
 dump_stack+0xa4/0xe5
 do_raw_spin_lock+0x20b/0x270
 ? rwlock_bug.part.1+0x90/0x90
 _raw_spin_lock_nested+0x5f/0x70
 bond_get_stats+0xe4/0x4c0 [bonding]
 ? rcu_read_lock_sched_held+0xc0/0xc0
 ? bond_neigh_init+0x2c0/0x2c0 [bonding]
 ? dev_get_alias+0xe2/0x190
 ? dev_get_port_parent_id+0x14a/0x360
 ? rtnl_unregister+0x190/0x190
 ? dev_get_phys_port_name+0xa0/0xa0
 ? memset+0x1f/0x40
 ? memcpy+0x38/0x60
 ? rtnl_phys_switch_id_fill+0x91/0x100
 dev_get_stats+0x8c/0x270
 rtnl_fill_stats+0x44/0xbe0
 ? nla_put+0xbe/0x140
 rtnl_fill_ifinfo+0x1054/0x3ad0
[ ... ]

Fixes: 272c2330 ("xfrm: bail early on slave pass over skb")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>