2 files changed, 73 insertions, 0 deletions

diff --git a/include/linux/net.h b/include/linux/net.h
index ca9ec8540905..a489705f6fa3 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -239,6 +239,31 @@ do {								\
 #define net_random()		prandom_u32()
 #define net_srandom(seed)	prandom_seed((__force u32)(seed))
 
+bool __net_get_random_once(void *buf, int nbytes, bool *done,
+			   struct static_key *done_key);
+
+#ifdef HAVE_JUMP_LABEL
+#define ___NET_RANDOM_STATIC_KEY_INIT ((struct static_key) \
+		{ .enabled = ATOMIC_INIT(0), .entries = (void *)1 })
+#else /* !HAVE_JUMP_LABEL */
+#define ___NET_RANDOM_STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
+#endif /* HAVE_JUMP_LABEL */
+
+/* BE CAREFUL: this function is not interrupt safe */
+#define net_get_random_once(buf, nbytes)				\
+	({								\
+		bool ___ret = false;					\
+		static bool ___done = false;				\
+		static struct static_key ___done_key =			\
+			___NET_RANDOM_STATIC_KEY_INIT;			\
+		if (!static_key_true(&___done_key))			\
+			___ret = __net_get_random_once(buf,		\
+						       nbytes,		\
+						       &___done,	\
+						       &___done_key);	\
+		___ret;							\
+	})
+
 int kernel_sendmsg(struct socket *sock, struct msghdr *msg, struct kvec *vec,
 		   size_t num, size_t len);
 int kernel_recvmsg(struct socket *sock, struct msghdr *msg, struct kvec *vec,
diff --git a/net/core/utils.c b/net/core/utils.c
index aa88e23fc87a..bf09371e19b1 100644
--- a/net/core/utils.c
+++ b/net/core/utils.c
@@ -338,3 +338,51 @@ void inet_proto_csum_replace16(__sum16 *sum, struct sk_buff *skb,
 				  csum_unfold(*sum)));
 }
 EXPORT_SYMBOL(inet_proto_csum_replace16);
+
+struct __net_random_once_work {
+	struct work_struct work;
+	struct static_key *key;
+};
+
+static void __net_random_once_deferred(struct work_struct *w)
+{
+	struct __net_random_once_work *work =
+		container_of(w, struct __net_random_once_work, work);
+	if (!static_key_enabled(work->key))
+		static_key_slow_inc(work->key);
+	kfree(work);
+}
+
+static void __net_random_once_disable_jump(struct static_key *key)
+{
+	struct __net_random_once_work *w;
+
+	w = kmalloc(sizeof(*w), GFP_ATOMIC);
+	if (!w)
+		return;
+
+	INIT_WORK(&w->work, __net_random_once_deferred);
+	w->key = key;
+	schedule_work(&w->work);
+}
+
+bool __net_get_random_once(void *buf, int nbytes, bool *done,
+			   struct static_key *done_key)
+{
+	static DEFINE_SPINLOCK(lock);
+
+	spin_lock_bh(&lock);
+	if (*done) {
+		spin_unlock_bh(&lock);
+		return false;
+	}
+
+	get_random_bytes(buf, nbytes);
+	*done = true;
+	spin_unlock_bh(&lock);
+
+	__net_random_once_disable_jump(done_key);
+
+	return true;
+}
+EXPORT_SYMBOL(__net_get_random_once);