nvme: fix NULL deref for fabrics options

git://git.infradead.org/nvme.git nvme-5.3 branch now causes the
following NULL deref oops.  Check the ctrl->opts first before the deref.

[   16.337581] BUG: kernel NULL pointer dereference, address: 0000000000000056
[   16.338551] #PF: supervisor read access in kernel mode
[   16.338551] #PF: error_code(0x0000) - not-present page
[   16.338551] PGD 0 P4D 0
[   16.338551] Oops: 0000 [#1] SMP PTI
[   16.338551] CPU: 2 PID: 1035 Comm: kworker/u16:5 Not tainted 5.2.0-rc6+ #1
[   16.338551] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.2-0-gf9626ccb91-prebuilt.qemu-project.org 04/01/2014
[   16.338551] Workqueue: nvme-wq nvme_scan_work [nvme_core]
[   16.338551] RIP: 0010:nvme_validate_ns+0xc9/0x7e0 [nvme_core]
[   16.338551] Code: c0 49 89 c5 0f 84 00 07 00 00 48 8b 7b 58 e8 be 48 39 c1 48 3d 00 f0 ff ff 49 89 45 18 0f 87 a4 06 00 00 48 8b 93 70 0a 00 00 <80> 7a 56 00 74 0c 48 8b 40 68 83 48 3c 08 49 8b 45 18 48 89 c6 bf
[   16.338551] RSP: 0018:ffffc900024c7d10 EFLAGS: 00010283
[   16.338551] RAX: ffff888135a30720 RBX: ffff88813a4fd1f8 RCX: 0000000000000007
[   16.338551] RDX: 0000000000000000 RSI: ffffffff8256dd38 RDI: ffff888135a30720
[   16.338551] RBP: 0000000000000001 R08: 0000000000000007 R09: ffff88813aa6a840
[   16.338551] R10: 0000000000000001 R11: 000000000002d060 R12: ffff88813a4fd1f8
[   16.338551] R13: ffff88813a77f800 R14: ffff88813aa35180 R15: 0000000000000001
[   16.338551] FS:  0000000000000000(0000) GS:ffff88813ba80000(0000) knlGS:0000000000000000
[   16.338551] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   16.338551] CR2: 0000000000000056 CR3: 000000000240a002 CR4: 0000000000360ee0
[   16.338551] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   16.338551] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   16.338551] Call Trace:
[   16.338551]  nvme_scan_work+0x2c0/0x340 [nvme_core]
[   16.338551]  ? __switch_to_asm+0x40/0x70
[   16.338551]  ? _raw_spin_unlock_irqrestore+0x18/0x30
[   16.338551]  ? try_to_wake_up+0x408/0x450
[   16.338551]  process_one_work+0x20b/0x3e0
[   16.338551]  worker_thread+0x1f9/0x3d0
[   16.338551]  ? cancel_delayed_work+0xa0/0xa0
[   16.338551]  kthread+0x117/0x120
[   16.338551]  ? kthread_stop+0xf0/0xf0
[   16.338551]  ret_from_fork+0x3a/0x50
[   16.338551] Modules linked in: nvme nvme_core
[   16.338551] CR2: 0000000000000056
[   16.338551] ---[ end trace b9bf761a93e62d84 ]---
[   16.338551] RIP: 0010:nvme_validate_ns+0xc9/0x7e0 [nvme_core]
[   16.338551] Code: c0 49 89 c5 0f 84 00 07 00 00 48 8b 7b 58 e8 be 48 39 c1 48 3d 00 f0 ff ff 49 89 45 18 0f 87 a4 06 00 00 48 8b 93 70 0a 00 00 <80> 7a 56 00 74 0c 48 8b 40 68 83 48 3c 08 49 8b 45 18 48 89 c6 bf
[   16.338551] RSP: 0018:ffffc900024c7d10 EFLAGS: 00010283
[   16.338551] RAX: ffff888135a30720 RBX: ffff88813a4fd1f8 RCX: 0000000000000007
[   16.338551] RDX: 0000000000000000 RSI: ffffffff8256dd38 RDI: ffff888135a30720
[   16.338551] RBP: 0000000000000001 R08: 0000000000000007 R09: ffff88813aa6a840
[   16.338551] R10: 0000000000000001 R11: 000000000002d060 R12: ffff88813a4fd1f8
[   16.338551] R13: ffff88813a77f800 R14: ffff88813aa35180 R15: 0000000000000001
[   16.338551] FS:  0000000000000000(0000) GS:ffff88813ba80000(0000) knlGS:0000000000000000
[   16.338551] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   16.338551] CR2: 0000000000000056 CR3: 000000000240a002 CR4: 0000000000360ee0
[   16.338551] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   16.338551] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Fixes: 958f2a0f ("nvme-tcp: set the STABLE_WRITES flag when data digests are enabled")
Cc: Christoph Hellwig <hch@lst.de>
Cc: Keith Busch <kbusch@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Minwoo Im <minwoo.im.dev@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/nvme/host/core.c

@@ -3305,7 +3305,7 @@ static int nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid)
 		goto out_free_ns;
 	}
 
-	if (ctrl->opts->data_digest)
+	if (ctrl->opts && ctrl->opts->data_digest)
 		ns->queue->backing_dev_info->capabilities
 			|= BDI_CAP_STABLE_WRITES;