On Thu, 28 May 2015 15:38:32 +0300
Lennert Buytenhek <buytenh@xxxxxxxxxxxxxx> wrote:
> 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.
Looks good to me. Even if this ends up being uneccessarily strict, we'll
always have a huge pool of addresses we may generate.
Note: the standard only says that the address shall be a 64 bit
universal address (not excluding multicast), but not generating
multicast EUIs seems like a good idea anyway.
> Signed-off-by: Lennert Buytenhek <buytenh@xxxxxxxxxxxxxx>
> ---
> include/linux/ieee802154.h | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/ieee802154.h b/include/linux/ieee802154.h
> index 8872ca1..552210d 100644
> --- a/include/linux/ieee802154.h
> +++ b/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 */
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