In the Linux kernel, the following vulnerability has been resolved:

scsi: hisi_sas: Create all dump files during debugfs initialization

For the current debugfs of hisi_sas, after user triggers dump, the
driver allocate memory space to save the register information and create
debugfs files to display the saved information. In this process, the
debugfs files created after each dump.

Therefore, when the dump is triggered while the driver is unbind, the
following hang occurs:

[67840.853907] Unable to handle kernel NULL pointer dereference at virtual address 00000000000000a0
[67840.862947] Mem abort info:
[67840.865855]   ESR = 0x0000000096000004
[67840.869713]   EC = 0x25: DABT (current EL), IL = 32 bits
[67840.875125]   SET = 0, FnV = 0
[67840.878291]   EA = 0, S1PTW = 0
[67840.881545]   FSC = 0x04: level 0 translation fault
[67840.886528] Data abort info:
[67840.889524]   ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
[67840.895117]   CM = 0, WnR = 0, TnD = 0, TagAccess = 0
[67840.900284]   GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[67840.905709] user pgtable: 4k pages, 48-bit VAs, pgdp=0000002803a1f000
[67840.912263] [00000000000000a0] pgd=0000000000000000, p4d=0000000000000000
[67840.919177] Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
[67840.996435] pstate: 80400009 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[67841.003628] pc : down_write+0x30/0x98
[67841.007546] lr : start_creating.part.0+0x60/0x198
[67841.012495] sp : ffff8000b979ba20
[67841.016046] x29: ffff8000b979ba20 x28: 0000000000000010 x27: 0000000000024b40
[67841.023412] x26: 0000000000000012 x25: ffff20202b355ae8 x24: ffff20202b35a8c8
[67841.030779] x23: ffffa36877928208 x22: ffffa368b4972240 x21: ffff8000b979bb18
[67841.038147] x20: ffff00281dc1e3c0 x19: fffffffffffffffe x18: 0000000000000020
[67841.045515] x17: 0000000000000000 x16: ffffa368b128a530 x15: ffffffffffffffff
[67841.052888] x14: ffff8000b979bc18 x13: ffffffffffffffff x12: ffff8000b979bb18
[67841.060263] x11: 0000000000000000 x10: 0000000000000000 x9 : ffffa368b1289b18
[67841.067640] x8 : 0000000000000012 x7 : 0000000000000000 x6 : 00000000000003a9
[67841.075014] x5 : 0000000000000000 x4 : ffff002818c5cb00 x3 : 0000000000000001
[67841.082388] x2 : 0000000000000000 x1 : ffff002818c5cb00 x0 : 00000000000000a0
[67841.089759] Call trace:
[67841.092456]  down_write+0x30/0x98
[67841.096017]  start_creating.part.0+0x60/0x198
[67841.100613]  debugfs_create_dir+0x48/0x1f8
[67841.104950]  debugfs_create_files_v3_hw+0x88/0x348 [hisi_sas_v3_hw]
[67841.111447]  debugfs_snapshot_regs_v3_hw+0x708/0x798 [hisi_sas_v3_hw]
[67841.118111]  debugfs_trigger_dump_v3_hw_write+0x9c/0x120 [hisi_sas_v3_hw]
[67841.125115]  full_proxy_write+0x68/0xc8
[67841.129175]  vfs_write+0xd8/0x3f0
[67841.132708]  ksys_write+0x70/0x108
[67841.136317]  __arm64_sys_write+0x24/0x38
[67841.140440]  invoke_syscall+0x50/0x128
[67841.144385]  el0_svc_common.constprop.0+0xc8/0xf0
[67841.149273]  do_el0_svc+0x24/0x38
[67841.152773]  el0_svc+0x38/0xd8
[67841.156009]  el0t_64_sync_handler+0xc0/0xc8
[67841.160361]  el0t_64_sync+0x1a4/0x1a8
[67841.164189] Code: b9000882 d2800002 d2800023 f9800011 (c85ffc05)
[67841.170443] ---[ end trace 0000000000000000 ]---

To fix this issue, create all directories and files during debugfs
initialization. In this way, the driver only needs to allocate memory
space to save information each time the user triggers dumping.

https://git.kernel.org/stable/c/6c55f99123075e5429850b41b06f7dfffcb708eb

https://git.kernel.org/stable/c/9f564f15f88490b484e02442dc4c4b11640ea172