[PATCH 5.16 0025/1017] locking/lockdep: Avoid potential access of invalid memory in lock_class

Greg Kroah-Hartman
2022-04-05T11:04:31Z

From: Waiman Long <longman@redhat.com>

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@i-love.sakura.ne.jp/

Fixes: 8b39adbee805 ("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>
Cc: Cheng-Jui Wang <cheng-jui.wang@mediatek.com>
Link: https://lkml.kernel.org/r/20220103023558.1377055-1-longman@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/locking/lockdep.c | 24 +++++++++++++++---------
1 file changed, 15 insertions(+), 9 deletions(-)

--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -6288,7 +6288,13 @@ 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);
@@ -6303,10 +6309,8 @@ 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);
@@ -6314,11 +6318,13 @@ 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. */