Describe CVE-2021-47284.
What is CVE-2021-47284?
In the Linux kernel, the following vulnerability has been resolved:

isdn: mISDN: netjet: Fix crash in nj_probe:

'nj_setup' in netjet.c might fail with -EIO and in this case
'card->irq' is initialized and is bigger than zero. A subsequent call to
'nj_release' will free the irq that has not been requested.

Fix this bug by deleting the previous assignment to 'card->irq' and just
keep the assignment before 'request_irq'.

The KASAN's log reveals it:

[    3.354615 ] WARNING: CPU: 0 PID: 1 at kernel/irq/manage.c:1826
free_irq+0x100/0x480
[    3.355112 ] Modules linked in:
[    3.355310 ] CPU: 0 PID: 1 Comm: swapper/0 Not tainted
5.13.0-rc1-00144-g25a1298726e #13
[    3.355816 ] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
[    3.356552 ] RIP: 0010:free_irq+0x100/0x480
[    3.356820 ] Code: 6e 08 74 6f 4d 89 f4 e8 5e ac 09 00 4d 8b 74 24 18
4d 85 f6 75 e3 e8 4f ac 09 00 8b 75 c8 48 c7 c7 78 c1 2e 85 e8 e0 cf f5
ff <0f> 0b 48 8b 75 c0 4c 89 ff e8 72 33 0b 03 48 8b 43 40 4c 8b a0 80
[    3.358012 ] RSP: 0000:ffffc90000017b48 EFLAGS: 00010082
[    3.358357 ] RAX: 0000000000000000 RBX: ffff888104dc8000 RCX:
0000000000000000
[    3.358814 ] RDX: ffff8881003c8000 RSI: ffffffff8124a9e6 RDI:
00000000ffffffff
[    3.359272 ] RBP: ffffc90000017b88 R08: 0000000000000000 R09:
0000000000000000
[    3.359732 ] R10: ffffc900000179f0 R11: 0000000000001d04 R12:
0000000000000000
[    3.360195 ] R13: ffff888107dc6000 R14: ffff888107dc6928 R15:
ffff888104dc80a8
[    3.360652 ] FS:  0000000000000000(0000) GS:ffff88817bc00000(0000)
knlGS:0000000000000000
[    3.361170 ] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    3.361538 ] CR2: 0000000000000000 CR3: 000000000582e000 CR4:
00000000000006f0
[    3.362003 ] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
0000000000000000
[    3.362175 ] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
0000000000000400
[    3.362175 ] Call Trace:
[    3.362175 ]  nj_release+0x51/0x1e0
[    3.362175 ]  nj_probe+0x450/0x950
[    3.362175 ]  ? pci_device_remove+0x110/0x110
[    3.362175 ]  local_pci_probe+0x45/0xa0
[    3.362175 ]  pci_device_probe+0x12b/0x1d0
[    3.362175 ]  really_probe+0x2a9/0x610
[    3.362175 ]  driver_probe_device+0x90/0x1d0
[    3.362175 ]  ? mutex_lock_nested+0x1b/0x20
[    3.362175 ]  device_driver_attach+0x68/0x70
[    3.362175 ]  __driver_attach+0x124/0x1b0
[    3.362175 ]  ? device_driver_attach+0x70/0x70
[    3.362175 ]  bus_for_each_dev+0xbb/0x110
[    3.362175 ]  ? rdinit_setup+0x45/0x45
[    3.362175 ]  driver_attach+0x27/0x30
[    3.362175 ]  bus_add_driver+0x1eb/0x2a0
[    3.362175 ]  driver_register+0xa9/0x180
[    3.362175 ]  __pci_register_driver+0x82/0x90
[    3.362175 ]  ? w6692_init+0x38/0x38
[    3.362175 ]  nj_init+0x36/0x38
[    3.362175 ]  do_one_initcall+0x7f/0x3d0
[    3.362175 ]  ? rdinit_setup+0x45/0x45
[    3.362175 ]  ? rcu_read_lock_sched_held+0x4f/0x80
[    3.362175 ]  kernel_init_freeable+0x2aa/0x301
[    3.362175 ]  ? rest_init+0x2c0/0x2c0
[    3.362175 ]  kernel_init+0x18/0x190
[    3.362175 ]  ? rest_init+0x2c0/0x2c0
[    3.362175 ]  ? rest_init+0x2c0/0x2c0
[    3.362175 ]  ret_from_fork+0x1f/0x30
[    3.362175 ] Kernel panic - not syncing: panic_on_warn set ...
[    3.362175 ] CPU: 0 PID: 1 Comm: swapper/0 Not tainted
5.13.0-rc1-00144-g25a1298726e #13
[    3.362175 ] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
[    3.362175 ] Call Trace:
[    3.362175 ]  dump_stack+0xba/0xf5
[    3.362175 ]  ? free_irq+0x100/0x480
[    3.362175 ]  panic+0x15a/0x3f2
[    3.362175 ]  ? __warn+0xf2/0x150
[    3.362175 ]  ? free_irq+0x100/0x480
[    3.362175 ]  __warn+0x108/0x150
[    3.362175 ]  ? free_irq+0x100/0x480
[    3.362175 ]  report_bug+0x119/0x1c0
[    3.362175 ]  handle_bug+0x3b/0x80
[    3.362175 ]  exc_invalid_op+0x18/0x70
[    3.362175 ]  asm_exc_invalid_op+0x12/0x20
[    3.362175 ] RIP: 0010:free_irq+0x100
---truncated---.