null_blk: return error for invalid zone size

In null_init_zone_dev() check if the zone size is larger than device
capacity, return error if needed.

This also fixes the following oops :-

null_blk: changed the number of conventional zones to 4294967295
BUG: kernel NULL pointer dereference, address: 0000000000000010
PGD 7d76c5067 P4D 7d76c5067 PUD 7d240c067 PMD 0
Oops: 0002 [#1] SMP NOPTI
CPU: 4 PID: 5508 Comm: nullbtests.sh Tainted: G OE 5.7.0-rc4lblk-fnext0
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba5276e4
RIP: 0010:null_init_zoned_dev+0x17a/0x27f [null_blk]
RSP: 0018:ffffc90007007e00 EFLAGS: 00010246
RAX: 0000000000000020 RBX: ffff8887fb3f3c00 RCX: 0000000000000007
RDX: 0000000000000000 RSI: ffff8887ca09d688 RDI: ffff888810fea510
RBP: 0000000000000010 R08: ffff8887ca09d688 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8887c26e8000
R13: ffffffffa05e9390 R14: 0000000000000000 R15: 0000000000000001
FS:  00007fcb5256f740(0000) GS:ffff888810e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000010 CR3: 000000081e8fe000 CR4: 00000000003406e0
Call Trace:
 null_add_dev+0x534/0x71b [null_blk]
 nullb_device_power_store.cold.41+0x8/0x2e [null_blk]
 configfs_write_file+0xe6/0x150
 vfs_write+0xba/0x1e0
 ksys_write+0x5f/0xe0
 do_syscall_64+0x60/0x250
 entry_SYSCALL_64_after_hwframe+0x49/0xb3
RIP: 0033:0x7fcb51c71840

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/null_blk_zoned.c

@@ -23,6 +23,10 @@ int null_init_zoned_dev(struct nullb_device *dev, struct request_queue *q)
 		pr_err("zone_size must be power-of-two\n");
 		return -EINVAL;
 	}
+	if (dev->zone_size > dev->size) {
+		pr_err("Zone size larger than device capacity\n");
+		return -EINVAL;
+	}
 
 	dev->zone_size_sects = dev->zone_size << ZONE_SIZE_SHIFT;
 	dev->nr_zones = dev_size >>