random: add get_random_{bytes,u32,u64,int,long,once}_wait family

These functions are simple convenience wrappers that call
wait_for_random_bytes before calling the respective get_random_*
function.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

include/linux/net.h

@@ -274,6 +274,8 @@ do {									\
 
 #define net_get_random_once(buf, nbytes)			\
 	get_random_once((buf), (nbytes))
+#define net_get_random_once_wait(buf, nbytes)			\
+	get_random_once_wait((buf), (nbytes))
 
 int kernel_sendmsg(struct socket *sock, struct msghdr *msg, struct kvec *vec,
 		   size_t num, size_t len);

include/linux/once.h

@@ -53,5 +53,7 @@ void __do_once_done(bool *done, struct static_key *once_key,
 
 #define get_random_once(buf, nbytes)					     \
 	DO_ONCE(get_random_bytes, (buf), (nbytes))
+#define get_random_once_wait(buf, nbytes)                                    \
+	DO_ONCE(get_random_bytes_wait, (buf), (nbytes))                      \
 
 #endif /* _LINUX_ONCE_H */

include/linux/random.h

@@ -58,6 +58,31 @@ static inline unsigned long get_random_long(void)
 #endif
 }
 
+/* Calls wait_for_random_bytes() and then calls get_random_bytes(buf, nbytes).
+ * Returns the result of the call to wait_for_random_bytes. */
+static inline int get_random_bytes_wait(void *buf, int nbytes)
+{
+	int ret = wait_for_random_bytes();
+	if (unlikely(ret))
+		return ret;
+	get_random_bytes(buf, nbytes);
+	return 0;
+}
+
+#define declare_get_random_var_wait(var) \
+	static inline int get_random_ ## var ## _wait(var *out) { \
+		int ret = wait_for_random_bytes(); \
+		if (unlikely(ret)) \
+			return ret; \
+		*out = get_random_ ## var(); \
+		return 0; \
+	}
+declare_get_random_var_wait(u32)
+declare_get_random_var_wait(u64)
+declare_get_random_var_wait(int)
+declare_get_random_var_wait(long)
+#undef declare_get_random_var
+
 unsigned long randomize_page(unsigned long start, unsigned long range);
 
 u32 prandom_u32(void);