In case unpair_device() was called through mgmt interface at the same time
when pairing was in progress, Bluetooth kernel module crash was seen.

[  600.351225] general protection fault: 0000 [#1] SMP PTI
[  600.351235] CPU: 1 PID: 11096 Comm: btmgmt Tainted: G           OE     4.19.0-rc1+ #1
[  600.351238] Hardware name: Dell Inc. Latitude E5440/08RCYC, BIOS A18 05/14/2017
[  600.351272] RIP: 0010:smp_chan_destroy.isra.10+0xce/0x2c0 [bluetooth]
[  600.351276] Code: c0 0f 84 b4 01 00 00 80 78 28 04 0f 84 53 01 00 00 4d 85 ed 0f 85 ab 00 00 00 48 8b 08 48 8b 50 08 be 10 00 00 00 48 89 51 08 <48> 89 0a 48 b9 00 02 00 00 00 00 ad de 48 89 48 08 48 8b 83 00 01
[  600.351279] RSP: 0018:ffffa9be839b3b50 EFLAGS: 00010246
[  600.351282] RAX: ffff9c999ac565a0 RBX: ffff9c9996e98c00 RCX: ffff9c999aa28b60
[  600.351285] RDX: dead000000000200 RSI: 0000000000000010 RDI: ffff9c999e403500
[  600.351287] RBP: ffffa9be839b3b70 R08: 0000000000000000 R09: ffffffff92a25c00
[  600.351290] R10: ffffa9be839b3ae8 R11: 0000000000000001 R12: ffff9c995375b800
[  600.351292] R13: 0000000000000000 R14: ffff9c99619a5000 R15: ffff9c9962a01c00
[  600.351295] FS:  00007fb2be27c700(0000) GS:ffff9c999e880000(0000) knlGS:0000000000000000
[  600.351298] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  600.351300] CR2: 00007fb2bdadbad0 CR3: 000000041c328001 CR4: 00000000001606e0
[  600.351302] Call Trace:
[  600.351325]  smp_failure+0x4f/0x70 [bluetooth]
[  600.351345]  smp_cancel_pairing+0x74/0x80 [bluetooth]
[  600.351370]  unpair_device+0x1c1/0x330 [bluetooth]
[  600.351399]  hci_sock_sendmsg+0x960/0x9f0 [bluetooth]
[  600.351409]  ? apparmor_socket_sendmsg+0x1e/0x20
[  600.351417]  sock_sendmsg+0x3e/0x50
[  600.351422]  sock_write_iter+0x85/0xf0
[  600.351429]  do_iter_readv_writev+0x12b/0x1b0
[  600.351434]  do_iter_write+0x87/0x1a0
[  600.351439]  vfs_writev+0x98/0x110
[  600.351443]  ? ep_poll+0x16d/0x3d0
[  600.351447]  ? ep_modify+0x73/0x170
[  600.351451]  do_writev+0x61/0xf0
[  600.351455]  ? do_writev+0x61/0xf0
[  600.351460]  __x64_sys_writev+0x1c/0x20
[  600.351465]  do_syscall_64+0x5a/0x110
[  600.351471]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[  600.351474] RIP: 0033:0x7fb2bdb62fe0
[  600.351477] Code: 73 01 c3 48 8b 0d b8 6e 2c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 83 3d 69 c7 2c 00 00 75 10 b8 14 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 de 80 01 00 48 89 04 24
[  600.351479] RSP: 002b:00007ffe062cb8f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
[  600.351484] RAX: ffffffffffffffda RBX: 000000000255b3d0 RCX: 00007fb2bdb62fe0
[  600.351487] RDX: 0000000000000001 RSI: 00007ffe062cb920 RDI: 0000000000000004
[  600.351490] RBP: 00007ffe062cb920 R08: 000000000255bd80 R09: 0000000000000000
[  600.351494] R10: 0000000000000353 R11: 0000000000000246 R12: 0000000000000001
[  600.351497] R13: 00007ffe062cbbe0 R14: 0000000000000000 R15: 0000000000000000
[  600.351501] Modules linked in: algif_hash algif_skcipher af_alg cmac ipt_MASQUERADE nf_conntrack_netlink nfnetlink xfrm_user xfrm_algo iptable_nat nf_nat_ipv4 xt_addrtype iptable_filter ip_tables xt_conntrack x_tables nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 libcrc32c br_netfilter bridge stp llc overlay arc4 nls_iso8859_1 dm_crypt intel_rapl x86_pkg_temp_thermal intel_powerclamp coretemp dell_laptop kvm_intel crct10dif_pclmul dell_smm_hwmon crc32_pclmul ghash_clmulni_intel pcbc aesni_intel aes_x86_64 crypto_simd cryptd glue_helper intel_cstate intel_rapl_perf uvcvideo videobuf2_vmalloc videobuf2_memops videobuf2_v4l2 videobuf2_common videodev media hid_multitouch input_leds joydev serio_raw dell_wmi snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic dell_smbios dcdbas sparse_keymap
[  600.351569]  snd_hda_intel btusb snd_hda_codec btrtl btbcm btintel snd_hda_core bluetooth(OE) snd_hwdep snd_pcm iwlmvm ecdh_generic wmi_bmof dell_wmi_descriptor snd_seq_midi mac80211 snd_seq_midi_event lpc_ich iwlwifi snd_rawmidi snd_seq snd_seq_device snd_timer cfg80211 snd soundcore mei_me mei dell_rbtn dell_smo8800 mac_hid parport_pc ppdev lp parport autofs4 hid_generic usbhid hid i915 nouveau kvmgt vfio_mdev mdev vfio_iommu_type1 vfio kvm irqbypass i2c_algo_bit ttm drm_kms_helper syscopyarea sysfillrect sysimgblt mxm_wmi psmouse ahci sdhci_pci cqhci libahci fb_sys_fops sdhci drm e1000e video wmi
[  600.351637] ---[ end trace e49e9f1df09c94fb ]---
[  600.351664] RIP: 0010:smp_chan_destroy.isra.10+0xce/0x2c0 [bluetooth]
[  600.351666] Code: c0 0f 84 b4 01 00 00 80 78 28 04 0f 84 53 01 00 00 4d 85 ed 0f 85 ab 00 00 00 48 8b 08 48 8b 50 08 be 10 00 00 00 48 89 51 08 <48> 89 0a 48 b9 00 02 00 00 00 00 ad de 48 89 48 08 48 8b 83 00 01
[  600.351669] RSP: 0018:ffffa9be839b3b50 EFLAGS: 00010246
[  600.351672] RAX: ffff9c999ac565a0 RBX: ffff9c9996e98c00 RCX: ffff9c999aa28b60
[  600.351674] RDX: dead000000000200 RSI: 0000000000000010 RDI: ffff9c999e403500
[  600.351676] RBP: ffffa9be839b3b70 R08: 0000000000000000 R09: ffffffff92a25c00
[  600.351679] R10: ffffa9be839b3ae8 R11: 0000000000000001 R12: ffff9c995375b800
[  600.351681] R13: 0000000000000000 R14: ffff9c99619a5000 R15: ffff9c9962a01c00
[  600.351684] FS:  00007fb2be27c700(0000) GS:ffff9c999e880000(0000) knlGS:0000000000000000
[  600.351686] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  600.351689] CR2: 00007fb2bdadbad0 CR3: 000000041c328001 CR4: 00000000001606e0

Crash happened because list_del_rcu() was called twice for smp->ltk. This
was possible if unpair_device was called right after ltk was generated
but before keys were distributed.

In this commit smp_cancel_pairing was refactored to cancel pairing if it
is in progress and otherwise just removes keys. Once keys are removed from
rcu list, pointers to smp context's keys are set to NULL to make sure
removed list items are not accessed later.

This commit also adjusts the functionality of mgmt unpair_device() little
bit. Previously pairing was canceled only if pairing was in state that
keys were already generated. With this commit unpair_device() cancels
pairing already in earlier states.

Bug was found by fuzzing kernel SMP implementation using Synopsys
Defensics.
Reported-by: Pekka Oikarainen <pekka.oikarainen@synopsys.com>
Signed-off-by: Matias Karhumaa <matias.karhumaa@gmail.com>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>