[PATCH v4 01/11] KEYS: Add key_gc_flush() for draining RCU callbacks

[Jarkko Sakkinen <jarkko@kernel.org>]

keyring_clear() and key_invalidate() release keyring links via call_rcu(),
and key_put() defers final key destruction to key_gc_work.

Once keys pin their type, callers that clear an internal cache before
module unload need a synchronous barrier so module references can be
dropped before delete_module() checks the refcount.

Add key_gc_flush() for flushing the remaining key_gc_work passes.

Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
 include/linux/key.h      |  2 ++
 security/keys/gc.c       | 21 +++++++++++++++++----
 security/keys/internal.h |  1 +
 security/keys/key.c      |  6 +++++-
 4 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/include/linux/key.h b/include/linux/key.h
index 420412aab926..0f408255f740 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -439,6 +439,7 @@ extern int restrict_link_reject(struct key *keyring,
 				struct key *restriction_key);
 
 extern int keyring_clear(struct key *keyring);
+void key_gc_flush(void);
 
 extern key_ref_t keyring_search(key_ref_t keyring,
 				struct key_type *type,
@@ -526,6 +527,7 @@ extern void key_init(void);
 #define key_free_user_ns(ns)		do { } while(0)
 #define key_remove_domain(d)		do { } while(0)
 #define key_lookup(k)			NULL
+#define key_gc_flush()			do { } while (0)
 
 #endif /* CONFIG_KEYS */
 #endif /* __KERNEL__ */
diff --git a/security/keys/gc.c b/security/keys/gc.c
index eda445f815d4..9b625436d3b5 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -19,8 +19,21 @@ unsigned key_gc_delay = 5 * 60;
  * Reaper for unused keys.
  */
 static void key_garbage_collector(struct work_struct *work);
+
+struct workqueue_struct *key_gc_wq __ro_after_init;
 DECLARE_WORK(key_gc_work, key_garbage_collector);
 
+/**
+ * key_gc_flush - Drain the garbage collector RCU callbacks
+ */
+void key_gc_flush(void)
+{
+	do {
+		rcu_barrier();
+	} while (flush_work(&key_gc_work));
+}
+EXPORT_SYMBOL_GPL(key_gc_flush);
+
 /*
  * Reaper for links from keyrings to dead keys.
  */
@@ -57,7 +70,7 @@ void key_schedule_gc(time64_t gc_at)
 
 	if (gc_at <= now || test_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags)) {
 		kdebug("IMMEDIATE");
-		schedule_work(&key_gc_work);
+		queue_work(key_gc_wq, &key_gc_work);
 	} else if (gc_at < key_gc_next_run) {
 		kdebug("DEFERRED");
 		key_gc_next_run = gc_at;
@@ -85,7 +98,7 @@ void key_set_expiry(struct key *key, time64_t expiry)
 void key_schedule_gc_links(void)
 {
 	set_bit(KEY_GC_KEY_EXPIRED, &key_gc_flags);
-	schedule_work(&key_gc_work);
+	queue_work(key_gc_wq, &key_gc_work);
 }
 
 /*
@@ -119,7 +132,7 @@ void key_gc_keytype(struct key_type *ktype)
 	set_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags);
 
 	kdebug("schedule");
-	schedule_work(&key_gc_work);
+	queue_work(key_gc_wq, &key_gc_work);
 
 	kdebug("sleep");
 	wait_on_bit(&key_gc_flags, KEY_GC_REAPING_KEYTYPE,
@@ -322,7 +335,7 @@ static void key_garbage_collector(struct work_struct *work)
 	}
 
 	if (gc_state & KEY_GC_REAP_AGAIN)
-		schedule_work(&key_gc_work);
+		queue_work(key_gc_wq, &key_gc_work);
 	kleave(" [end %x]", gc_state);
 	return;
 
diff --git a/security/keys/internal.h b/security/keys/internal.h
index b7b622bc36a1..84f14307552b 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -164,6 +164,7 @@ extern void key_change_session_keyring(struct callback_head *twork);
 
 extern struct work_struct key_gc_work;
 extern unsigned key_gc_delay;
+extern struct workqueue_struct *key_gc_wq;
 extern void keyring_gc(struct key *keyring, time64_t limit);
 extern void keyring_restriction_gc(struct key *keyring,
 				   struct key_type *dead_type);
diff --git a/security/keys/key.c b/security/keys/key.c
index 3f1f0fc13710..3e604d25d35e 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -670,7 +670,7 @@ void key_put(struct key *key)
 			}
 			/* Mark key as safe for GC after key->user done. */
 			clear_bit_unlock(KEY_FLAG_USER_ALIVE, &key->flags);
-			schedule_work(&key_gc_work);
+			queue_work(key_gc_wq, &key_gc_work);
 		}
 	}
 }
@@ -1294,6 +1294,10 @@ void __init key_init(void)
 	key_jar = kmem_cache_create("key_jar", sizeof(struct key),
 			0, SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_NO_MERGE, NULL);
 
+	key_gc_wq = alloc_workqueue("key_gc", WQ_MEM_RECLAIM | WQ_PERCPU, 0);
+	if (!key_gc_wq)
+		panic("Cannot create key_gc workqueue\n");
+
 	/* add the special key types */
 	list_add_tail(&key_type_keyring.link, &key_types_list);
 	list_add_tail(&key_type_dead.link, &key_types_list);
-- 
2.47.3