random: replace custom notifier chain with standard one

We previously rolled our own randomness readiness notifier, which only
has two users in the whole kernel. Replace this with a more standard
atomic notifier block that serves the same purpose with less code. Also
unexport the symbols, because no modules use it, only unconditional
builtins. The only drawback is that it's possible for a notification
handler returning the "stop" code to prevent further processing, but
given that there are only two users, and that we're unexporting this
anyway, that doesn't seem like a significant drawback for the
simplification we receive here.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

1 files changed, 19 insertions, 48 deletions

diff --git a/drivers/char/random.c b/drivers/char/random.c
index bc2a4f7e3655..aa7bc9a3a864 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -83,8 +83,8 @@ static int crng_init = 0;
 /* Various types of waiters for crng_init->2 transition. */
 static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
 static struct fasync_struct *fasync;
-static DEFINE_SPINLOCK(random_ready_list_lock);
-static LIST_HEAD(random_ready_list);
+static DEFINE_SPINLOCK(random_ready_chain_lock);
+static RAW_NOTIFIER_HEAD(random_ready_chain);
 
 /* Control how we warn userspace. */
 static struct ratelimit_state unseeded_warning =
@@ -144,72 +144,43 @@ EXPORT_SYMBOL(wait_for_random_bytes);
  *
  * returns: 0 if callback is successfully added
  *	    -EALREADY if pool is already initialised (callback not called)
- *	    -ENOENT if module for callback is not alive
  */
-int add_random_ready_callback(struct random_ready_callback *rdy)
+int register_random_ready_notifier(struct notifier_block *nb)
 {
-	struct module *owner;
 	unsigned long flags;
-	int err = -EALREADY;
+	int ret = -EALREADY;
 
 	if (crng_ready())
-		return err;
-
-	owner = rdy->owner;
-	if (!try_module_get(owner))
-		return -ENOENT;
-
-	spin_lock_irqsave(&random_ready_list_lock, flags);
-	if (crng_ready())
-		goto out;
-
-	owner = NULL;
-
-	list_add(&rdy->list, &random_ready_list);
-	err = 0;
-
-out:
-	spin_unlock_irqrestore(&random_ready_list_lock, flags);
-
-	module_put(owner);
+		return ret;
 
-	return err;
+	spin_lock_irqsave(&random_ready_chain_lock, flags);
+	if (!crng_ready())
+		ret = raw_notifier_chain_register(&random_ready_chain, nb);
+	spin_unlock_irqrestore(&random_ready_chain_lock, flags);
+	return ret;
 }
-EXPORT_SYMBOL(add_random_ready_callback);
 
 /*
  * Delete a previously registered readiness callback function.
  */
-void del_random_ready_callback(struct random_ready_callback *rdy)
+int unregister_random_ready_notifier(struct notifier_block *nb)
 {
 	unsigned long flags;
-	struct module *owner = NULL;
-
-	spin_lock_irqsave(&random_ready_list_lock, flags);
-	if (!list_empty(&rdy->list)) {
-		list_del_init(&rdy->list);
-		owner = rdy->owner;
-	}
-	spin_unlock_irqrestore(&random_ready_list_lock, flags);
+	int ret;
 
-	module_put(owner);
+	spin_lock_irqsave(&random_ready_chain_lock, flags);
+	ret = raw_notifier_chain_unregister(&random_ready_chain, nb);
+	spin_unlock_irqrestore(&random_ready_chain_lock, flags);
+	return ret;
 }
-EXPORT_SYMBOL(del_random_ready_callback);
 
 static void process_random_ready_list(void)
 {
 	unsigned long flags;
-	struct random_ready_callback *rdy, *tmp;
 
-	spin_lock_irqsave(&random_ready_list_lock, flags);
-	list_for_each_entry_safe(rdy, tmp, &random_ready_list, list) {
-		struct module *owner = rdy->owner;
-
-		list_del_init(&rdy->list);
-		rdy->func(rdy);
-		module_put(owner);
-	}
-	spin_unlock_irqrestore(&random_ready_list_lock, flags);
+	spin_lock_irqsave(&random_ready_chain_lock, flags);
+	raw_notifier_call_chain(&random_ready_chain, 0, NULL);
+	spin_unlock_irqrestore(&random_ready_chain_lock, flags);
 }
 
 #define warn_unseeded_randomness(previous) \