Issue: padata: UAF in padata_serial_worker reproduce

[Wang Jinchao]

Hello, I have reproduced the issue mentioned by Nicolai Stange on an arm64 server.
After applying Nicolai Stange's patch, the issue did not reoccur even after running for two days.
The test tools used were ltp20220121 and stress-ng-0.15.06.tar.gz.

refurl: https://lore.kernel.org/all/20221028160401.cccypv4euxikusiq@parnassus.localdomain/T/#u

The testing steps were as follows:
1. Enabled the KASAN (Kernel Address Sanitizer) feature.
2. Applied CPU and memory stress to the physical machine, each at 80% load:
   ```
   stress=$(($(cat /proc/cpuinfo | grep "processor" | wc -l) * 80 / 100))
   stress-ng --vm 1 --vm-bytes 80% -c $stress -t 168h
   ```
3. Applied stress to the filesystem:
   ```
   stress-ng --sequential 1 --class filesystem --exclude "io,iomix" --timeout 168h --verbose --metrics-brief --times
   ```
4. Ran the LTP (Linux Test Project) test for approximately 4 hours, which resulted in the KASAN logs:
   ```
   ./runltp -s pcrypt_aead01
   ```



[  788.732881] ==================================================================
[  788.740821] BUG: KASAN: slab-use-after-free in padata_serial_worker+0x20c/0x320
[  788.748837] Write of size 4 at addr ffff002102d37018 by task kworker/1:2/664

[  788.758835] CPU: 1 PID: 664 Comm: kworker/1:2 Kdump: loaded Not tainted 6.6.0-rc1-dirty #5
[  788.767769] Hardware name: Huawei S920X00/BC82AMDYA, BIOS 1.99 01/06/2023
[  788.775247] Workqueue: pdecrypt_serial padata_serial_worker
[  788.781529] Call trace:
[  788.784687]  dump_backtrace+0xa0/0x128
[  788.789145]  show_stack+0x20/0x38
[  788.793171]  dump_stack_lvl+0x78/0xc8
[  788.797531]  print_address_description.constprop.0+0x84/0x2b0
[  788.803979]  kasan_report+0xe0/0x118
[  788.808282]  kasan_check_range+0xe8/0x190
[  788.812980]  __kasan_check_write+0x20/0x30
[  788.817783]  padata_serial_worker+0x20c/0x320
[  788.822868]  process_one_work+0x310/0x638
[  788.827594]  worker_thread+0x424/0x650
[  788.832054]  kthread+0x164/0x178
[  788.836000]  ret_from_fork+0x10/0x20

[  788.842484] Allocated by task 215792:
[  788.846863]  kasan_save_stack+0x2c/0x58
[  788.851426]  kasan_set_track+0x2c/0x40
[  788.855893]  kasan_save_alloc_info+0x24/0x38
[  788.860868]  __kasan_kmalloc+0xa0/0xb8
[  788.865319]  kmalloc_trace+0x64/0xf8
[  788.869613]  padata_alloc_pd+0x48/0x370
[  788.874140]  padata_alloc_shell+0x5c/0x120
[  788.878932]  pcrypt_create_aead.isra.0+0x98/0x280 [pcrypt]
[  788.885139]  pcrypt_create+0x6c/0x88 [pcrypt]
[  788.890189]  cryptomgr_probe+0x58/0xe0
[  788.894639]  kthread+0x164/0x178
[  788.898565]  ret_from_fork+0x10/0x20

[  788.905040] Freed by task 149081:
[  788.909041]  kasan_save_stack+0x2c/0x58
[  788.913577]  kasan_set_track+0x2c/0x40
[  788.918015]  kasan_save_free_info+0x38/0x60
[  788.922885]  __kasan_slab_free+0xe8/0x168
[  788.927584]  __kmem_cache_free+0x130/0x298
[  788.932373]  kfree+0x78/0x108
[  788.936037]  padata_free_shell+0xe0/0x120
[  788.940736]  pcrypt_free+0x38/0x68 [pcrypt]
[  788.945620]  crypto_aead_free_instance+0x34/0x50
[  788.950930]  crypto_destroy_instance_workfn+0x50/0x80
[  788.956666]  process_one_work+0x310/0x638
[  788.961378]  worker_thread+0x424/0x650
[  788.965841]  kthread+0x164/0x178
[  788.969763]  ret_from_fork+0x10/0x20