ocfs2: rebase copied fsdlm LVB pointers in locking_state

Overview

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

ocfs2: rebase copied fsdlm LVB pointers in locking_state

The locking_state debugfs iterator snapshots struct ocfs2_lock_res by value under ocfs2_dlm_tracking_lock and later formats that copy in ocfs2_dlm_seq_show(). That is fine for the inline fields, but the userspace fsdlm stack stores the LVB through lksb_fsdlm.sb_lvbptr. Once the iterator drops the tracking lock, a copied non-NULL sb_lvbptr still points into the original lockres owner, so teardown can free that container before the debugfs dump walks the raw LVB bytes.

Rebase the copied sb_lvbptr to the copied l_lksb before dumping the raw LVB. The seq snapshot already carries the inline LVB storage reserved in struct ocfs2_dlm_lksb, so the debugfs reader can dump the copied bytes without borrowing the original lockres lifetime.

The buggy scenario involves two paths, with each column showing the order within that path:

locking_state reader: lockres teardown:

1. ocfs2_dlm_seq_start()/next() 1. file release or another owner copies struct ocfs2_lock_res teardown reaches
2. ocfs2_dlm_seq_show() formats ocfs2_lock_res_free() the copied row 2. the lockres is removed from the
3. ocfs2_dlm_lvb() follows the tracking list copied sb_lvbptr 3. the owner frees the original lockres container

Validation reproduced this kernel report: KASAN slab-use-after-free in ocfs2_dlm_seq_show+0x1bd/0x430 RIP: 0033:0x7f8ec4b1e29d The buggy address belongs to the object at ffff88810a1e0800 which belongs to the cache kmalloc-1k of size 1024 The buggy address is located 368 bytes inside of freed 1024-byte region [ffff88810a1e0800, ffff88810a1e0c00) Read of size 1 Call trace: dump_stack_lvl+0x66/0xa0 print_report+0xce/0x630 ocfs2_dlm_seq_show+0x1bd/0x430 (fs/ocfs2/dlmglue.c:3137) srso_alias_return_thunk+0x5/0xfbef5 __virt_addr_valid+0x19f/0x330 kasan_report+0xe0/0x110 seq_read_iter+0x29d/0x790 seq_read+0x20a/0x280 find_held_lock+0x2b/0x80 rcu_read_unlock+0x18/0x70 full_proxy_read+0x9e/0xd0 vfs_read+0x12c/0x590 ksys_read+0xd2/0x170 do_user_addr_fault+0x65a/0x890 do_syscall_64+0x115/0x6a0 (arch/x86/entry/syscall_64.c:87) entry_SYSCALL_64_after_hwframe+0x77/0x7f Allocated by task stack: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 __kasan_kmalloc+0xaa/0xb0 ocfs2_file_open+0x13e/0x300 do_dentry_open+0x233/0x7f0 vfs_open+0x5a/0x1b0 path_openat+0x66d/0x1540 do_file_open+0x186/0x2b0 do_sys_openat2+0xce/0x150 __x64_sys_openat+0xd0/0x140 do_syscall_64+0x115/0x6a0 (arch/x86/entry/syscall_64.c:87) entry_SYSCALL_64_after_hwframe+0x77/0x7f Freed by task stack: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 kasan_save_free_info+0x3b/0x60 __kasan_slab_free+0x5f/0x80 kfree+0x313/0x590 ocfs2_file_release+0x138/0x260 __fput+0x1df/0x4b0 fput_close_sync+0xd2/0x170 __x64_sys_close+0x55/0x90 do_syscall_64+0x115/0x6a0 (arch/x86/entry/syscall_64.c:87) entry_SYSCALL_64_after_hwframe+0x77/0x7f

Affected

• Linux >= cf4d8d75d8aba537a19b313a9364fd08ddbd5622 < 185427b5f7a209254c85c18aad5a4a8e009b2f30
• Linux >= cf4d8d75d8aba537a19b313a9364fd08ddbd5622 < 07aa4a8ebacde3d0ba50f60d2964f274ee7629bc
• Linux >= cf4d8d75d8aba537a19b313a9364fd08ddbd5622 < e037c1250cc90e7aacb002357d1b0399fc65ecfc
• Linux >= cf4d8d75d8aba537a19b313a9364fd08ddbd5622 < 6b38a5b8ee951e5b244e9a3c3d28d0f5e7c51411
• Linux >= cf4d8d75d8aba537a19b313a9364fd08ddbd5622 < 8614a8f7e81edd34c9f67e454e7024fd12a2a341
• Linux >= cf4d8d75d8aba537a19b313a9364fd08ddbd5622 < bb44a7690a4d553da705919cf666a80f5ca9011c
• Linux >= cf4d8d75d8aba537a19b313a9364fd08ddbd5622 < 610a0d2a35496738e1472fb0f318d5008a1c634f
• Linux >= cf4d8d75d8aba537a19b313a9364fd08ddbd5622 < 93612d48fa42b3d1a637eb9279e15281c611c000
• Linux 2.6.26

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.