CVE-2022-48674

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

erofs: fix pcluster use-after-free on UP platforms

During stress testing with CONFIG_SMP disabled, KASAN reports as below:

==================================================================

BUG: KASAN: use-after-free in __mutex_lock+0xe5/0xc30

Read of size 8 at addr ffff8881094223f8 by task stress/7789

CPU: 0 PID: 7789 Comm: stress Not tainted 6.0.0-rc1-00002-g0d53d2e882f9 #3

Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011

Call Trace:

<TASK>

..

__mutex_lock+0xe5/0xc30

..

z_erofs_do_read_page+0x8ce/0x1560

..

z_erofs_readahead+0x31c/0x580

..

Freed by task 7787

kasan_save_stack+0x1e/0x40

kasan_set_track+0x20/0x30

kasan_set_free_info+0x20/0x40

__kasan_slab_free+0x10c/0x190

kmem_cache_free+0xed/0x380

rcu_core+0x3d5/0xc90

__do_softirq+0x12d/0x389

Last potentially related work creation:

kasan_save_stack+0x1e/0x40

__kasan_record_aux_stack+0x97/0xb0

call_rcu+0x3d/0x3f0

erofs_shrink_workstation+0x11f/0x210

erofs_shrink_scan+0xdc/0x170

shrink_slab.constprop.0+0x296/0x530

drop_slab+0x1c/0x70

drop_caches_sysctl_handler+0x70/0x80

proc_sys_call_handler+0x20a/0x2f0

vfs_write+0x555/0x6c0

ksys_write+0xbe/0x160

do_syscall_64+0x3b/0x90

The root cause is that erofs_workgroup_unfreeze() doesn't reset to

orig_val thus it causes a race that the pcluster reuses unexpectedly

before freeing.

Since UP platforms are quite rare now, such path becomes unnecessary.

Let's drop such specific-designed path directly instead.