Describe CVE-2021-47440.
What is CVE-2021-47440?
In the Linux kernel, the following vulnerability has been resolved:

net: encx24j600: check error in devm_regmap_init_encx24j600

devm_regmap_init may return error which caused by like out of memory,
this will results in null pointer dereference later when reading
or writing register:

general protection fault in encx24j600_spi_probe
KASAN: null-ptr-deref in range [0x0000000000000090-0x0000000000000097]
CPU: 0 PID: 286 Comm: spi-encx24j600- Not tainted 5.15.0-rc2-00142-g9978db750e31-dirty #11 9c53a778c1306b1b02359f3c2bbedc0222cba652
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
RIP: 0010:regcache_cache_bypass drivers/base/regmap/regcache.c:540
Code: 54 41 89 f4 55 53 48 89 fb 48 83 ec 08 e8 26 94 a8 fe 48 8d bb a0 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 4a 03 00 00 4c 8d ab b0 00 00 00 48 8b ab a0 00
RSP: 0018:ffffc900010476b8 EFLAGS: 00010207
RAX: dffffc0000000000 RBX: fffffffffffffff4 RCX: 0000000000000000
RDX: 0000000000000012 RSI: ffff888002de0000 RDI: 0000000000000094
RBP: ffff888013c9a000 R08: 0000000000000000 R09: fffffbfff3f9cc6a
R10: ffffc900010476e8 R11: fffffbfff3f9cc69 R12: 0000000000000001
R13: 000000000000000a R14: ffff888013c9af54 R15: ffff888013c9ad08
FS:  00007ffa984ab580(0000) GS:ffff88801fe00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055a6384136c8 CR3: 000000003bbe6003 CR4: 0000000000770ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
 encx24j600_spi_probe drivers/net/ethernet/microchip/encx24j600.c:459
 spi_probe drivers/spi/spi.c:397
 really_probe drivers/base/dd.c:517
 __driver_probe_device drivers/base/dd.c:751
 driver_probe_device drivers/base/dd.c:782
 __device_attach_driver drivers/base/dd.c:899
 bus_for_each_drv drivers/base/bus.c:427
 __device_attach drivers/base/dd.c:971
 bus_probe_device drivers/base/bus.c:487
 device_add drivers/base/core.c:3364
 __spi_add_device drivers/spi/spi.c:599
 spi_add_device drivers/spi/spi.c:641
 spi_new_device drivers/spi/spi.c:717
 new_device_store+0x18c/0x1f1 [spi_stub 4e02719357f1ff33f5a43d00630982840568e85e]
 dev_attr_store drivers/base/core.c:2074
 sysfs_kf_write fs/sysfs/file.c:139
 kernfs_fop_write_iter fs/kernfs/file.c:300
 new_sync_write fs/read_write.c:508 (discriminator 4)
 vfs_write fs/read_write.c:594
 ksys_write fs/read_write.c:648
 do_syscall_64 arch/x86/entry/common.c:50
 entry_SYSCALL_64_after_hwframe arch/x86/entry/entry_64.S:113

Add error check in devm_regmap_init_encx24j600 to avoid this situation..