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, ixgbevf should always use real_dev instead of dev.
Of course, real_dev always not be null.

Test commands:
    ip link add bond0 type bond
    #eth0 is ixgbevf interface
    ip link set eth0 master bond0
    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:
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 6 PID: 688 Comm: ip Not tainted 5.13.0-rc3+ #1168
RIP: 0010:ixgbevf_ipsec_find_empty_idx+0x28/0x1b0 [ixgbevf]
Code: 00 00 0f 1f 44 00 00 55 53 48 89 fb 48 83 ec 08 40 84 f6 0f 84 9c
00 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> b6 04 02
84 c0 74 08 3c 01 0f 8e 4c 01 00 00 66 81 3b 00 04 0f
RSP: 0018:ffff8880089af390 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000001
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffff8880089af4f8 R08: 0000000000000003 R09: fffffbfff4287e11
R10: 0000000000000001 R11: ffff888005de8908 R12: 0000000000000000
R13: ffff88810936a000 R14: ffff88810936a000 R15: ffff888004d78040
FS:  00007fdf9883a680(0000) GS:ffff88811a400000(0000)
knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055bc14adbf40 CR3: 000000000b87c005 CR4: 00000000003706e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 ixgbevf_ipsec_add_sa+0x1bf/0x9c0 [ixgbevf]
 ? rcu_read_lock_sched_held+0x91/0xc0
 ? ixgbevf_ipsec_parse_proto_keys.isra.9+0x280/0x280 [ixgbevf]
 ? lock_acquire+0x191/0x720
 ? bond_ipsec_add_sa+0x48/0x350 [bonding]
 ? lockdep_hardirqs_on_prepare+0x3e0/0x3e0
 ? rcu_read_lock_held+0x91/0xa0
 ? rcu_read_lock_sched_held+0xc0/0xc0
 bond_ipsec_add_sa+0x193/0x350 [bonding]
 xfrm_dev_state_add+0x2a9/0x770
 ? memcpy+0x38/0x60
 xfrm_add_sa+0x2278/0x3b10 [xfrm_user]
 ? xfrm_get_policy+0xaa0/0xaa0 [xfrm_user]
 ? register_lock_class+0x1750/0x1750
 xfrm_user_rcv_msg+0x331/0x660 [xfrm_user]
 ? rcu_read_lock_sched_held+0x91/0xc0
 ? xfrm_user_state_lookup.constprop.39+0x320/0x320 [xfrm_user]
 ? find_held_lock+0x3a/0x1c0
 ? mutex_lock_io_nested+0x1210/0x1210
 ? sched_clock_cpu+0x18/0x170
 netlink_rcv_skb+0x121/0x350
[ ... ]

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>