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: .. __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() doesnt 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. Lets drop such specific-designed path directly instead.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/2f44013e39984c127c6efedf70e6b5f4e9dcf315
• https://git.kernel.org/stable/c/8ddd001cef5e82d19192e6861068463ecca5f556
• https://git.kernel.org/stable/c/94c34faaafe7b55adc2d8d881db195b646959b9e
• https://git.kernel.org/stable/c/2f44013e39984c127c6efedf70e6b5f4e9dcf315
• https://git.kernel.org/stable/c/8ddd001cef5e82d19192e6861068463ecca5f556
• https://git.kernel.org/stable/c/94c34faaafe7b55adc2d8d881db195b646959b9e