This patch fixes kernel NULL pointer dereference when creating nexthop
which is bound with SRv6 decapsulation. In the creation of nexthop,
__seg6_end_dt_vrf_build is called. __seg6_end_dt_vrf_build expects
fc_lninfo in fib6_config is set correctly, but it isn't set in
nh_create_ipv6, which causes kernel crash.

Here is steps to reproduce kernel crash:

1. modprobe vrf
2. ip -6 nexthop add encap seg6local action End.DT4 vrftable 1 dev eth0

We got the following message:

[  901.370336] BUG: kernel NULL pointer dereference, address: 0000000000000ba0
[  901.371658] #PF: supervisor read access in kernel mode
[  901.372672] #PF: error_code(0x0000) - not-present page
[  901.373672] PGD 0 P4D 0
[  901.374248] Oops: 0000 [#1] SMP PTI
[  901.374944] CPU: 0 PID: 8593 Comm: ip Not tainted 5.14-051400-generic #202108310811-Ubuntu
[  901.376404] Hardware name: Red Hat KVM, BIOS 1.11.1-4.module_el8.2.0+320+13f867d7 04/01/2014
[  901.377907] RIP: 0010:vrf_ifindex_lookup_by_table_id+0x19/0x90 [vrf]
[  901.379182] Code: c1 e9 72 ff ff ff e8 96 49 01 c2 66 0f 1f 44 00 00 0f 1f 44 00 00 55 48 89 e5 41 56 41 55 41 89 f5 41 54 53 8b 05 47 4c 00 00 <48> 8b 97 a0 0b 00 00 48 8b 1c c2 e8 57 27 53 c1 4c 8d a3 88 00 00
[  901.382652] RSP: 0018:ffffbf2d02043590 EFLAGS: 00010282
[  901.383746] RAX: 000000000000000b RBX: ffff990808255e70 RCX: ffffbf2d02043aa8
[  901.385436] RDX: 0000000000000001 RSI: 0000000000000001 RDI: 0000000000000000
[  901.386924] RBP: ffffbf2d020435b0 R08: 00000000000000c0 R09: ffff990808255e40
[  901.388537] R10: ffffffff83b08c90 R11: 0000000000000009 R12: 0000000000000000
[  901.389937] R13: 0000000000000001 R14: 0000000000000000 R15: 000000000000000b
[  901.391226] FS:  00007fe49381f740(0000) GS:ffff99087dc00000(0000) knlGS:0000000000000000
[  901.392737] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  901.393803] CR2: 0000000000000ba0 CR3: 000000000e3e8003 CR4: 0000000000770ef0
[  901.395122] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  901.396496] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  901.397833] PKRU: 55555554
[  901.398578] Call Trace:
[  901.399144]  l3mdev_ifindex_lookup_by_table_id+0x3b/0x70
[  901.400179]  __seg6_end_dt_vrf_build+0x34/0xd0
[  901.401067]  seg6_end_dt4_build+0x16/0x20
[  901.401904]  seg6_local_build_state+0x271/0x430
[  901.402797]  lwtunnel_build_state+0x81/0x130
[  901.403645]  fib_nh_common_init+0x82/0x100
[  901.404465]  ? sock_def_readable+0x4b/0x80
[  901.405285]  fib6_nh_init+0x115/0x7c0
[  901.406033]  nh_create_ipv6.isra.0+0xe1/0x140
[  901.406932]  rtm_new_nexthop+0x3b7/0xeb0
[  901.407828]  rtnetlink_rcv_msg+0x152/0x3a0
[  901.408663]  ? rtnl_calcit.isra.0+0x130/0x130
[  901.409535]  netlink_rcv_skb+0x55/0x100
[  901.410319]  rtnetlink_rcv+0x15/0x20
[  901.411026]  netlink_unicast+0x1a8/0x250
[  901.411813]  netlink_sendmsg+0x238/0x470
[  901.412602]  ? _copy_from_user+0x2b/0x60
[  901.413394]  sock_sendmsg+0x65/0x70
[  901.414112]  ____sys_sendmsg+0x218/0x290
[  901.414929]  ? copy_msghdr_from_user+0x5c/0x90
[  901.415814]  ___sys_sendmsg+0x81/0xc0
[  901.416559]  ? fsnotify_destroy_marks+0x27/0xf0
[  901.417447]  ? call_rcu+0xa4/0x230
[  901.418153]  ? kmem_cache_free+0x23f/0x410
[  901.418972]  ? dentry_free+0x37/0x70
[  901.419705]  ? mntput_no_expire+0x4c/0x260
[  901.420574]  __sys_sendmsg+0x62/0xb0
[  901.421297]  __x64_sys_sendmsg+0x1f/0x30
[  901.422057]  do_syscall_64+0x5c/0xc0
[  901.422756]  ? syscall_exit_to_user_mode+0x27/0x50
[  901.423675]  ? __x64_sys_close+0x12/0x40
[  901.424462]  ? do_syscall_64+0x69/0xc0
[  901.425219]  ? irqentry_exit_to_user_mode+0x9/0x20
[  901.426149]  ? irqentry_exit+0x19/0x30
[  901.426901]  ? exc_page_fault+0x89/0x160
[  901.427709]  ? asm_exc_page_fault+0x8/0x30
[  901.428536]  entry_SYSCALL_64_after_hwframe+0x44/0xae
[  901.429514] RIP: 0033:0x7fe493945747
[  901.430248] Code: 64 89 02 48 c7 c0 ff ff ff ff eb bb 0f 1f 80 00 00 00 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 89 54 24 1c 48 89 74 24 10
[  901.433549] RSP: 002b:00007ffe9932cf68 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
[  901.434981] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fe493945747
[  901.436303] RDX: 0000000000000000 RSI: 00007ffe9932cfe0 RDI: 0000000000000003
[  901.437607] RBP: 00000000613053f7 R08: 0000000000000001 R09: 00007ffe9932d07c
[  901.438990] R10: 000055f4a903a010 R11: 0000000000000246 R12: 0000000000000001
[  901.440340] R13: 0000000000000001 R14: 000055f4a802b163 R15: 000055f4a8042020
[  901.441630] Modules linked in: vrf nls_utf8 isofs nls_iso8859_1 dm_multipath scsi_dh_rdac scsi_dh_emc scsi_dh_alua intel_rapl_msr intel_rapl_common isst_if_mbox_msr isst_if_common nfit rapl input_leds joydev serio_raw qemu_fw_cfg mac_hid sch_fq_codel drm virtio_rng ip_tables x_tables autofs4 btrfs blake2b_generic zstd_compress raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq libcrc32c raid1 raid0 multipath linear crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel crypto_simd virtio_net net_failover cryptd psmouse virtio_blk failover i2c_piix4 pata_acpi floppy
[  901.450808] CR2: 0000000000000ba0
[  901.451514] ---[ end trace c27b934b99ade304 ]---
[  901.452403] RIP: 0010:vrf_ifindex_lookup_by_table_id+0x19/0x90 [vrf]
[  901.453626] Code: c1 e9 72 ff ff ff e8 96 49 01 c2 66 0f 1f 44 00 00 0f 1f 44 00 00 55 48 89 e5 41 56 41 55 41 89 f5 41 54 53 8b 05 47 4c 00 00 <48> 8b 97 a0 0b 00 00 48 8b 1c c2 e8 57 27 53 c1 4c 8d a3 88 00 00
[  901.456910] RSP: 0018:ffffbf2d02043590 EFLAGS: 00010282
[  901.457912] RAX: 000000000000000b RBX: ffff990808255e70 RCX: ffffbf2d02043aa8
[  901.459238] RDX: 0000000000000001 RSI: 0000000000000001 RDI: 0000000000000000
[  901.460552] RBP: ffffbf2d020435b0 R08: 00000000000000c0 R09: ffff990808255e40
[  901.461882] R10: ffffffff83b08c90 R11: 0000000000000009 R12: 0000000000000000
[  901.463208] R13: 0000000000000001 R14: 0000000000000000 R15: 000000000000000b
[  901.464529] FS:  00007fe49381f740(0000) GS:ffff99087dc00000(0000) knlGS:0000000000000000
[  901.466058] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  901.467189] CR2: 0000000000000ba0 CR3: 000000000e3e8003 CR4: 0000000000770ef0
[  901.468515] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  901.469858] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  901.471139] PKRU: 55555554
Signed-off-by: Ryoga Saito <contact@proelbtn.com>
Signed-off-by: David S. Miller <davem@davemloft.net>