From: Waiman Long <longman@xxxxxxxxxx> commit 61cc4534b6550997c97a03759ab46b29d44c0017 upstream. It was found that reading /proc/lockdep after a lockdep splat may potentially cause an access to freed memory if lockdep_unregister_key() is called after the splat but before access to /proc/lockdep [1]. This is due to the fact that graph_lock() call in lockdep_unregister_key() fails after the clearing of debug_locks by the splat process. After lockdep_unregister_key() is called, the lock_name may be freed but the corresponding lock_class structure still have a reference to it. That invalid memory pointer will then be accessed when /proc/lockdep is read by a user and a use-after-free (UAF) error will be reported if KASAN is enabled. To fix this problem, lockdep_unregister_key() is now modified to always search for a matching key irrespective of the debug_locks state and zap the corresponding lock class if a matching one is found. [1] https://lore.kernel.org/lkml/77f05c15-81b6-bddd-9650-80d5f23fe330@xxxxxxxxxxxxxxxxxxx/ Fixes: 8b39adbee805 ("locking/lockdep: Make lockdep_unregister_key() honor 'debug_locks' again") Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Waiman Long <longman@xxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Reviewed-by: Bart Van Assche <bvanassche@xxxxxxx> Cc: Cheng-Jui Wang <cheng-jui.wang@xxxxxxxxxxxx> Link: https://lkml.kernel.org/r/20220103023558.1377055-1-longman@xxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/locking/lockdep.c | 24 +++++++++++++++--------- 1 file changed, 15 insertions(+), 9 deletions(-) --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -6290,7 +6290,13 @@ void lockdep_reset_lock(struct lockdep_m lockdep_reset_lock_reg(lock); } -/* Unregister a dynamically allocated key. */ +/* + * Unregister a dynamically allocated key. + * + * Unlike lockdep_register_key(), a search is always done to find a matching + * key irrespective of debug_locks to avoid potential invalid access to freed + * memory in lock_class entry. + */ void lockdep_unregister_key(struct lock_class_key *key) { struct hlist_head *hash_head = keyhashentry(key); @@ -6305,10 +6311,8 @@ void lockdep_unregister_key(struct lock_ return; raw_local_irq_save(flags); - if (!graph_lock()) - goto out_irq; + lockdep_lock(); - pf = get_pending_free(); hlist_for_each_entry_rcu(k, hash_head, hash_entry) { if (k == key) { hlist_del_rcu(&k->hash_entry); @@ -6316,11 +6320,13 @@ void lockdep_unregister_key(struct lock_ break; } } - WARN_ON_ONCE(!found); - __lockdep_free_key_range(pf, key, 1); - call_rcu_zapped(pf); - graph_unlock(); -out_irq: + WARN_ON_ONCE(!found && debug_locks); + if (found) { + pf = get_pending_free(); + __lockdep_free_key_range(pf, key, 1); + call_rcu_zapped(pf); + } + lockdep_unlock(); raw_local_irq_restore(flags); /* Wait until is_dynamic_key() has finished accessing k->hash_entry. */
