hashtables: use rdrand() instead of counter

3 files changed, 7 insertions, 5 deletions

diff --git a/src/hashtables.c b/src/hashtables.c
index 965605b..2fb4322 100644
--- a/src/hashtables.c
+++ b/src/hashtables.c
@@ -61,7 +61,6 @@ static inline struct hlist_head *index_bucket(struct index_hashtable *table, con
 void index_hashtable_init(struct index_hashtable *table)
 {
 	get_random_bytes(table->key, SIPHASH24_KEY_LEN);
-	atomic64_set(&table->counter, 0);
 	hash_init(table->hashtable);
 	spin_lock_init(&table->lock);
 }
@@ -69,7 +68,7 @@ void index_hashtable_init(struct index_hashtable *table)
 __le32 index_hashtable_insert(struct index_hashtable *table, struct index_hashtable_entry *entry)
 {
 	struct index_hashtable_entry *existing_entry;
-	uint64_t counter;
+	uint64_t rand;
 
 	spin_lock(&table->lock);
 	hlist_del_init_rcu(&entry->index_hash);
@@ -79,8 +78,8 @@ __le32 index_hashtable_insert(struct index_hashtable *table, struct index_hashta
 
 search_unused_slot:
 	/* First we try to find an unused slot, randomly, while unlocked. */
-	counter = atomic64_inc_return(&table->counter);
-	entry->index = (__force __le32)siphash24((uint8_t *)&counter, sizeof(counter), table->key);
+	rand = get_random_long();
+	entry->index = (__force __le32)siphash24((uint8_t *)&rand, sizeof(rand), table->key);
 	hlist_for_each_entry_rcu(existing_entry, index_bucket(table, entry->index), index_hash) {
 		if (existing_entry->index == entry->index)
 			goto search_unused_slot; /* If it's already in use, we continue searching. */
diff --git a/src/hashtables.h b/src/hashtables.h
index d51c0d8..89845f6 100644
--- a/src/hashtables.h
+++ b/src/hashtables.h
@@ -21,7 +21,6 @@ struct wireguard_peer *pubkey_hashtable_lookup(struct pubkey_hashtable *table, c
 struct index_hashtable {
 	DECLARE_HASHTABLE(hashtable, 10);
 	uint8_t key[SIPHASH24_KEY_LEN];
-	atomic64_t counter;
 	spinlock_t lock;
 };
 struct index_hashtable_entry;
diff --git a/src/wireguard.h b/src/wireguard.h
index 5c83ab6..2985323 100644
--- a/src/wireguard.h
+++ b/src/wireguard.h
@@ -36,6 +36,10 @@
 #define net_dbg_ratelimited(fmt, ...) do { if (0) no_printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__); } while (0)
 #endif
 
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 5, 0)
+#define get_random_long() (((u64)get_random_int() << 32) | get_random_int())
+#endif
+
 struct wireguard_device {
 	struct sock __rcu *sock4, *sock6;
 	u16 incoming_port;