ieee802154: Fix generation of random EUI-64 addresses.

Currently, ieee802154_random_extended_addr() has a 50% chance of
generating a group (multicast) address, while this function is used
for generating station addresses (which can't be group addresses)
for interfaces that don't have a hardware-provided address.

Also, in case get_random_bytes() generates the EUI-64 address
00:00:00:00:00:00:00:00 (extremely unlikely), which is an invalid
address, ieee802154_random_extended_addr() reacts by changing it
to 01:00:00:00:00:00:00:00, which is an invalid station address as
well, as it is a group address.

This patch changes the address generation procedure to grab eight
random bytes, treat that as an EUI-64, and then clear the Group
address bit and set the Locally Administered bit, which is in
line with how eth_random_addr() generates random EUI-48s.

Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Acked-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

include/linux/ieee802154.h

@@ -244,9 +244,9 @@ static inline void ieee802154_random_extended_addr(__le64 *addr)
 {
 	get_random_bytes(addr, IEEE802154_EXTENDED_ADDR_LEN);
 
-	/* toggle some bit if we hit an invalid extended addr */
-	if (!ieee802154_is_valid_extended_addr(*addr))
-		((u8 *)addr)[IEEE802154_EXTENDED_ADDR_LEN - 1] ^= 0x01;
+	/* clear the group bit, and set the locally administered bit */
+	((u8 *)addr)[IEEE802154_EXTENDED_ADDR_LEN - 1] &= ~0x01;
+	((u8 *)addr)[IEEE802154_EXTENDED_ADDR_LEN - 1] |= 0x02;
 }
 
 #endif /* LINUX_IEEE802154_H */