Linux kernel OCFS2 DLM: debugfs read can use freed recovery memory

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

ocfs2/dlm: Protect the recovery list during debugfs reads

Recovery participant records must remain alive while debug_state_print() walks reco.node_data and formats their fields. The formatter holds dlm->spinlock, but the recovery participant list is protected by dlm_reco_state_lock. In particular, dlm_destroy_recovery_area() detaches the list under dlm_reco_state_lock and frees the detached records after releasing it. A concurrent debugfs open can therefore read freed memory.

Protect the participant traversal and field reads in debug_state_print() with dlm_reco_state_lock, matching the existing list writers. This also serializes the traversal against list_add_tail() during recovery-area initialization. Make the existing lock available to the debug code through dlmcommon.h; the lock remains internal to the OCFS2 DLM module.

Release dlm->spinlock after formatting the other domain state and before acquiring dlm_reco_state_lock, so the debug reader does not nest the two locks. Leave recovery list insertion, detachment and freeing unchanged.

KASAN report as below:

BUG: KASAN: slab-use-after-free in debug_state_open+0x1169/0x12d0
Read of size 4 at addr ffff88810662ef80 by task dlm-state-stres/896

CPU: 1 UID: 0 PID: 896 Comm: dlm-state-stres Not tainted 7.3.0-rc4-next-20260921-pmb-ocfs2-functional-v1+ #1 PREEMPT(lazy)
Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x93/0xd0
 print_report+0xce/0x630
 ? debug_state_open+0x1169/0x12d0
 ? srso_alias_return_thunk+0x5/0xfbef5
 ? __virt_addr_valid+0x20e/0x420
 ? debug_state_open+0x1169/0x12d0
 kasan_report+0xe0/0x110
 ? debug_state_open+0x1169/0x12d0
 debug_state_open+0x1169/0x12d0
 ? __pfx_debug_state_open+0x10/0x10
 full_proxy_open_regular+0x193/0x310
 do_dentry_open+0x595/0x12d0
 ? __pfx_full_proxy_open_regular+0x10/0x10
 vfs_open_consume+0xd1/0x400
 ? srso_alias_return_thunk+0x5/0xfbef5
 path_openat+0x18d0/0x2020
 ? __pfx_path_openat+0x10/0x10
 do_file_open+0x21e/0x470
 ? __pfx_do_file_open+0x10/0x10
 ? _raw_spin_unlock+0x23/0x40
 ? srso_alias_return_thunk+0x5/0xfbef5
 ? alloc_fd+0x3a6/0x6b0
 do_sys_openat2+0xf4/0x1b0
 ? __pfx_do_sys_openat2+0x10/0x10
 ? srso_alias_return_thunk+0x5/0xfbef5
 ? __fput+0x5b5/0xa60
 __x64_sys_openat+0x136/0x1e0
 ? __pfx___x64_sys_openat+0x10/0x10
 do_syscall_64+0x114/0x620
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
[Register dump omitted.]
 </TASK>

Allocated by task 880:
 kasan_save_stack+0x33/0x60
 kasan_save_track+0x14/0x30
 __kasan_kmalloc+0xaa/0xb0
 __kmalloc_cache_noprof+0x28d/0x610
 dlm_remaster_locks+0x147/0x1d90
 dlm_do_recovery+0xde1/0x1580
 dlm_recovery_thread+0x109/0x300
 kthread+0x351/0x460
 ret_from_fork+0x659/0x940
 ret_from_fork_asm+0x1a/0x30

Freed by task 880:
 kasan_save_stack+0x33/0x60
 kasan_save_track+0x14/0x30
 kasan_save_free_info+0x3b/0x60
 __kasan_slab_free+0x5f/0x80
 kfree+0x308/0x580
 dlm_destroy_recovery_area+0x285/0x460
 dlm_remaster_locks+0x17c4/0x1d90
 dlm_do_recovery+0xde1/0x1580
 dlm_recovery_thread+0x109/0x300
 kthread+0x351/0x460
 ret_from_fork+0x659/0x940
 ret_from_fork_asm+0x1a/0x30

The buggy address belongs to the object at ffff88810662ef80
 which belongs to the cache kmalloc-32 of size 32
The buggy address is located 0 bytes inside of
 freed 32-byte region [ffff88810662ef80, ffff88810662efa0)

[Page and memory-state dumps omitted.]