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FAILED: patch "[PATCH] locking/lockdep: Avoid potential access of invalid memory in" failed to apply to 5.4-stable tree

PATCH [email protected] 1 participant 1 message Mar 29, 2022

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The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 61cc4534b6550997c97a03759ab46b29d44c0017 Mon Sep 17 00:00:00 2001
From: Waiman Long <[email protected]>
Date: Sun, 2 Jan 2022 21:35:58 -0500
Subject: [PATCH] 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/[email protected]/

Fixes 8b39adbee805 ("locking/lockdep: Make lockdep_unregister_key() honor 'debug_locks' again")
Reported-by Tetsuo Handa <[email protected]>
Signed-off-by Waiman Long <[email protected]>
Signed-off-by Peter Zijlstra (Intel) <[email protected]>
Reviewed-by Bart Van Assche <[email protected]>
Link https://lkml.kernel.org/r/[email protected] open here
kernel/locking/lockdep.c +15 -9
index 89b3df51fd98..2e6892ec3756 100644
@@ -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);
-	__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. */