Bluetooth: Use correct tfm to generate OOB data

In case local OOB data was generated and other device initiated pairing
claiming that it has got OOB data, following crash occurred:

[  222.847853] general protection fault: 0000 [#1] SMP PTI
[  222.848025] CPU: 1 PID: 42 Comm: kworker/u5:0 Tainted: G         C        4.18.0-custom #4
[  222.848158] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
[  222.848307] Workqueue: hci0 hci_rx_work [bluetooth]
[  222.848416] RIP: 0010:compute_ecdh_secret+0x5a/0x270 [bluetooth]
[  222.848540] Code: 0c af f5 48 8b 3d 46 de f0 f6 ba 40 00 00 00 be c0 00 60 00 e8 b7 7b c5 f5 48 85 c0 0f 84 ea 01 00 00 48 89 c3 e8 16 0c af f5 <49> 8b 47 38 be c0 00 60 00 8b 78 f8 48 83 c7 48 e8 51 84 c5 f5 48
[  222.848914] RSP: 0018:ffffb1664087fbc0 EFLAGS: 00010293
[  222.849021] RAX: ffff8a5750d7dc00 RBX: ffff8a5671096780 RCX: ffffffffc08bc32a
[  222.849111] RDX: 0000000000000000 RSI: 00000000006000c0 RDI: ffff8a5752003800
[  222.849192] RBP: ffffb1664087fc60 R08: ffff8a57525280a0 R09: ffff8a5752003800
[  222.849269] R10: ffffb1664087fc70 R11: 0000000000000093 R12: ffff8a5674396e00
[  222.849350] R13: ffff8a574c2e79aa R14: ffff8a574c2e796a R15: 020e0e100d010101
[  222.849429] FS:  0000000000000000(0000) GS:ffff8a5752500000(0000) knlGS:0000000000000000
[  222.849518] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  222.849586] CR2: 000055856016a038 CR3: 0000000110d2c005 CR4: 00000000000606e0
[  222.849671] Call Trace:
[  222.849745]  ? sc_send_public_key+0x110/0x2a0 [bluetooth]
[  222.849825]  ? sc_send_public_key+0x115/0x2a0 [bluetooth]
[  222.849925]  smp_recv_cb+0x959/0x2490 [bluetooth]
[  222.850023]  ? _cond_resched+0x19/0x40
[  222.850105]  ? mutex_lock+0x12/0x40
[  222.850202]  l2cap_recv_frame+0x109d/0x3420 [bluetooth]
[  222.850315]  ? l2cap_recv_frame+0x109d/0x3420 [bluetooth]
[  222.850426]  ? __switch_to_asm+0x34/0x70
[  222.850515]  ? __switch_to_asm+0x40/0x70
[  222.850625]  ? __switch_to_asm+0x34/0x70
[  222.850724]  ? __switch_to_asm+0x40/0x70
[  222.850786]  ? __switch_to_asm+0x34/0x70
[  222.850846]  ? __switch_to_asm+0x40/0x70
[  222.852581]  ? __switch_to_asm+0x34/0x70
[  222.854976]  ? __switch_to_asm+0x40/0x70
[  222.857475]  ? __switch_to_asm+0x40/0x70
[  222.859775]  ? __switch_to_asm+0x34/0x70
[  222.861218]  ? __switch_to_asm+0x40/0x70
[  222.862327]  ? __switch_to_asm+0x34/0x70
[  222.863758]  l2cap_recv_acldata+0x266/0x3c0 [bluetooth]
[  222.865122]  hci_rx_work+0x1c9/0x430 [bluetooth]
[  222.867144]  process_one_work+0x210/0x4c0
[  222.868248]  worker_thread+0x41/0x4d0
[  222.869420]  kthread+0x141/0x160
[  222.870694]  ? process_one_work+0x4c0/0x4c0
[  222.871668]  ? kthread_create_worker_on_cpu+0x90/0x90
[  222.872896]  ret_from_fork+0x35/0x40
[  222.874132] Modules linked in: algif_hash algif_skcipher af_alg rfcomm bnep btusb btrtl btbcm btintel snd_intel8x0 cmac intel_rapl_perf vboxvideo(C) snd_ac97_codec bluetooth ac97_bus joydev ttm snd_pcm ecdh_generic drm_kms_helper snd_timer snd input_leds drm serio_raw fb_sys_fops soundcore syscopyarea sysfillrect sysimgblt mac_hid sch_fq_codel ib_iser rdma_cm iw_cm ib_cm ib_core iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi ip_tables x_tables autofs4 btrfs zstd_compress raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq libcrc32c raid1 raid0 multipath linear hid_generic usbhid hid crct10dif_pclmul crc32_pclmul ghash_clmulni_intel pcbc aesni_intel aes_x86_64 crypto_simd cryptd glue_helper ahci psmouse libahci i2c_piix4 video e1000 pata_acpi
[  222.883153] fbcon_switch: detected unhandled fb_set_par error, error code -16
[  222.886774] fbcon_switch: detected unhandled fb_set_par error, error code -16
[  222.890503] ---[ end trace 6504aa7a777b5316 ]---
[  222.890541] RIP: 0010:compute_ecdh_secret+0x5a/0x270 [bluetooth]
[  222.890551] Code: 0c af f5 48 8b 3d 46 de f0 f6 ba 40 00 00 00 be c0 00 60 00 e8 b7 7b c5 f5 48 85 c0 0f 84 ea 01 00 00 48 89 c3 e8 16 0c af f5 <49> 8b 47 38 be c0 00 60 00 8b 78 f8 48 83 c7 48 e8 51 84 c5 f5 48
[  222.890555] RSP: 0018:ffffb1664087fbc0 EFLAGS: 00010293
[  222.890561] RAX: ffff8a5750d7dc00 RBX: ffff8a5671096780 RCX: ffffffffc08bc32a
[  222.890565] RDX: 0000000000000000 RSI: 00000000006000c0 RDI: ffff8a5752003800
[  222.890571] RBP: ffffb1664087fc60 R08: ffff8a57525280a0 R09: ffff8a5752003800
[  222.890576] R10: ffffb1664087fc70 R11: 0000000000000093 R12: ffff8a5674396e00
[  222.890581] R13: ffff8a574c2e79aa R14: ffff8a574c2e796a R15: 020e0e100d010101
[  222.890586] FS:  0000000000000000(0000) GS:ffff8a5752500000(0000) knlGS:0000000000000000
[  222.890591] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  222.890594] CR2: 000055856016a038 CR3: 0000000110d2c005 CR4: 00000000000606e0

This commit fixes a bug where invalid pointer to crypto tfm was used for
SMP SC ECDH calculation when OOB was in use. Solution is to use same
crypto tfm than when generating OOB material on generate_oob() function.

This bug was introduced in commit c0153b0b901a ("Bluetooth: let the crypto
subsystem generate the ecc privkey"). Bug was found by fuzzing kernel SMP
implementation using Synopsys Defensics.

Signed-off-by: Matias Karhumaa <matias.karhumaa@gmail.com>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/smp.c

@@ -2700,7 +2700,13 @@ static int smp_cmd_public_key(struct l2cap_conn *conn, struct sk_buff *skb)
 	 * key was set/generated.
 	 */
 	if (test_bit(SMP_FLAG_LOCAL_OOB, &smp->flags)) {
-		struct smp_dev *smp_dev = chan->data;
+		struct l2cap_chan *hchan = hdev->smp_data;
+		struct smp_dev *smp_dev;
+
+		if (!hchan || !hchan->data)
+			return SMP_UNSPECIFIED;
+
+		smp_dev = hchan->data;
 
 		tfm_ecdh = smp_dev->tfm_ecdh;
 	} else {