fs: dlm: fix use after free in midcomms commit
CVE: CVE-2023-53629
Component: kernel
CWE: CWE-416
Severity: Moderate
CVSS v3: 4.9/AV:A/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
Release date: 2023-01-01T00:00:00+00:00

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

fs: dlm: fix use after free in midcomms commit

While working on processing dlm message in softirq context I experienced
the following KASAN use-after-free warning:

[  151.760477] ==================================================================
[  151.761803] BUG: KASAN: use-after-free in dlm_midcomms_commit_mhandle+0x19d/0x4b0
[  151.763414] Read of size 4 at addr ffff88811a980c60 by task lock_torture/1347

[  151.765284] CPU: 7 PID: 1347 Comm: lock_torture Not tainted 6.1.0-rc4+ #2828
[  151.766778] Hardware name: Red Hat KVM/RHEL-AV, BIOS 1.16.0-3.module+el8.7.0+16134+e5908aa2 04/01/2014
[  151.768726] Call Trace:
[  151.769277]  <TASK>
[  151.769748]  dump_stack_lvl+0x5b/0x86
[  151.770556]  print_report+0x180/0x4c8
[  151.771378]  ? kasan_complete_mode_report_info+0x7c/0x1e0
[  151.772241]  ? dlm_midcomms_commit_mhandle+0x19d/0x4b0
[  151.773069]  kasan_report+0x93/0x1a0
[  151.773668]  ? dlm_midcomms_commit_mhandle+0x19d/0x4b0
[  151.774514]  __asan_load4+0x7e/0xa0
[  151.775089]  dlm_midcomms_commit_mhandle+0x19d/0x4b0
[  151.775890]  ? create_message.isra.29.constprop.64+0x57/0xc0
[  151.776770]  send_common+0x19f/0x1b0
[  151.777342]  ? remove_from_waiters+0x60/0x60
[  151.778017]  ? lock_downgrade+0x410/0x410
[  151.778648]  ? __this_cpu_preempt_check+0x13/0x20
[  151.779421]  ? rcu_lockdep_current_cpu_online+0x88/0xc0
[  151.780292]  _convert_lock+0x46/0x150
[  151.780893]  convert_lock+0x7b/0xc0
[  151.781459]  dlm_lock+0x3ac/0x580
[  151.781993]  ? 0xffffffffc0540000
[  151.782522]  ? torture_stop+0x120/0x120 [dlm_locktorture]
[  151.783379]  ? dlm_scan_rsbs+0xa70/0xa70
[  151.784003]  ? preempt_count_sub+0xd6/0x130
[  151.784661]  ? is_module_address+0x47/0x70
[  151.785309]  ? torture_stop+0x120/0x120 [dlm_locktorture]
[  151.786166]  ? 0xffffffffc0540000
[  151.786693]  ? lockdep_init_map_type+0xc3/0x360
[  151.787414]  ? 0xffffffffc0540000
[  151.787947]  torture_dlm_lock_sync.isra.3+0xe9/0x150 [dlm_locktorture]
[  151.789004]  ? torture_stop+0x120/0x120 [dlm_locktorture]
[  151.789858]  ? 0xffffffffc0540000
[  151.790392]  ? lock_torture_cleanup+0x20/0x20 [dlm_locktorture]
[  151.791347]  ? delay_tsc+0x94/0xc0
[  151.791898]  torture_ex_iter+0xc3/0xea [dlm_locktorture]
[  151.792735]  ? torture_start+0x30/0x30 [dlm_locktorture]
[  151.793606]  lock_torture+0x177/0x270 [dlm_locktorture]
[  151.794448]  ? torture_dlm_lock_sync.isra.3+0x150/0x150 [dlm_locktorture]
[  151.795539]  ? lock_torture_stats+0x80/0x80 [dlm_locktorture]
[  151.796476]  ? do_raw_spin_lock+0x11e/0x1e0
[  151.797152]  ? mark_held_locks+0x34/0xb0
[  151.797784]  ? _raw_spin_unlock_irqrestore+0x30/0x70
[  151.798581]  ? __kthread_parkme+0x79/0x110
[  151.799246]  ? trace_preempt_on+0x2a/0xf0
[  151.799902]  ? __kthread_parkme+0x79/0x110
[  151.800579]  ? preempt_count_sub+0xd6/0x130
[  151.801271]  ? __kasan_check_read+0x11/0x20
[  151.801963]  ? __kthread_parkme+0xec/0x110
[  151.802630]  ? lock_torture_stats+0x80/0x80 [dlm_locktorture]
[  151.803569]  kthread+0x192/0x1d0
[  151.804104]  ? kthread_complete_and_exit+0x30/0x30
[  151.804881]  ret_from_fork+0x1f/0x30
[  151.805480]  </TASK>

[  151.806111] Allocated by task 1347:
[  151.806681]  kasan_save_stack+0x26/0x50
[  151.807308]  kasan_set_track+0x25/0x30
[  151.807920]  kasan_save_alloc_info+0x1e/0x30
[  151.808609]  __kasan_slab_alloc+0x63/0x80
[  151.809263]  kmem_cache_alloc+0x1ad/0x830
[  151.809916]  dlm_allocate_mhandle+0x17/0x20
[  151.810590]  dlm_midcomms_get_mhandle+0x96/0x260
[  151.811344]  _create_message+0x95/0x180
[  151.811994]  create_message.isra.29.constprop.64+0x57/0xc0
[  151.812880]  send_common+0x129/0x1b0
[  151.813467]  _convert_lock+0x46/0x150
[  151.814074]  convert_lock+0x7b/0xc0
[  151.814648]  dlm_lock+0x3ac/0x580
[  151.815199]  torture_dlm_lock_sync.isra.3+0xe9/0x150 [dlm_locktorture]
[  151.816258]  torture_ex_iter+0xc3/0xea [dlm_locktorture]
[  151.817129]  lock_t
---truncated---

Statement: A race in DLM midcomms (dlm_midcomms_commit_mhandle() for v3.2) could free a message handle upon an early ACK while it’s still being used, leading to a kernel UAF and crash. The fix surrounds the commit path with RCU read locking to prevent premature reclamation.

Remediation: