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locking/lockdep: Avoid potential access of invalid memory in lock_class 

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@i-love.sakura.ne.jp/

Fixes: 8b39adbee8 ("locking/lockdep: Make lockdep_unregister_key() honor 'debug_locks' again")
Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lkml.kernel.org/r/20220103023558.1377055-1-longman@redhat.com
This commit is contained in:
Waiman Long 2022-01-02 21:35:58 -05:00 committed by Peter Zijlstra
parent e204193b13
commit 61cc4534b6
1 changed files with 15 additions and 9 deletions
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20
kernel/locking/lockdep.c
View File

@ -6287,7 +6287,13 @@ void lockdep_reset_lock(struct lockdep_map *lock)
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);
@ -6302,10 +6308,8 @@ void lockdep_unregister_key(struct lock_class_key *key)
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);
@ -6313,11 +6317,13 @@ void lockdep_unregister_key(struct lock_class_key *key)
break;
}
}
WARN_ON_ONCE(!found);
WARN_ON_ONCE(!found && debug_locks);
if (found) {
pf = get_pending_free();
__lockdep_free_key_range(pf, key, 1);
call_rcu_zapped(pf);
graph_unlock();
out_irq:
}
lockdep_unlock();
raw_local_irq_restore(flags);
/* Wait until is_dynamic_key() has finished accessing k->hash_entry. */