On 2/20/18 9:43 AM, Sabrina Dubroca wrote:
> According to RFC 4429 (section 3.1), adding new IPv6 addresses as
> optimistic addresses is acceptable, as long as the implementation
> follows some rules:
>
> * Optimistic DAD SHOULD only be used when the implementation is aware
> that the address is based on a most likely unique interface
> identifier (such as in [RFC2464]), generated randomly [RFC3041],
> or by a well-distributed hash function [RFC3972] or assigned by
> Dynamic Host Configuration Protocol for IPv6 (DHCPv6) [RFC3315].
> Optimistic DAD SHOULD NOT be used for manually entered
> addresses.
That last line suggests this patch should not be allowed.
But if it is ...
>
> Thus, it seems reasonable to allow userspace to set the optimistic flag
> when adding new addresses.
>
> We must not let userspace set NODAD + OPTIMISTIC, since if the kernel is
> not performing DAD we would never clear the optimistic flag. We must
> also ignore userspace's request to add OPTIMISTIC flag to addresses that
> have already completed DAD.
>
> Then we also need to clear the OPTIMISTIC flag on permanent addresses
> when DAD fails. Otherwise, IFA_F_OPTIMISTIC addresses added by userspace
> can still be used after DAD has failed, because in
> ipv6_chk_addr_and_flags(), IFA_F_OPTIMISTIC overrides IFA_F_TENTATIVE.
>
> Signed-off-by: Sabrina Dubroca <s...@queasysnail.net>
> ---
> net/ipv6/addrconf.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 4facfe0b1888..652285bae801 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -1968,6 +1968,7 @@ static void addrconf_dad_stop(struct inet6_ifaddr *ifp,
> int dad_failed)
> spin_lock_bh(&ifp->lock);
> addrconf_del_dad_work(ifp);
> ifp->flags |= IFA_F_TENTATIVE;
> + ifp->flags &= ~IFA_F_OPTIMISTIC;
> spin_unlock_bh(&ifp->lock);
> if (dad_failed)
> ipv6_ifa_notify(0, ifp);
> @@ -4501,6 +4502,9 @@ static int inet6_addr_modify(struct inet6_ifaddr *ifp,
> u32 ifa_flags,
> (ifp->flags & IFA_F_TEMPORARY || ifp->prefix_len != 64))
> return -EINVAL;
>
> + if (!(ifp->flags & (IFA_F_TENTATIVE | IFA_F_DADFAILED)))
> + ifa_flags &= ~IFA_F_OPTIMISTIC;
> +
> timeout = addrconf_timeout_fixup(valid_lft, HZ);
> if (addrconf_finite_timeout(timeout)) {
> expires = jiffies_to_clock_t(timeout * HZ);
> @@ -4607,7 +4611,10 @@ inet6_rtm_newaddr(struct sk_buff *skb, struct nlmsghdr
> *nlh,
>
> /* We ignore other flags so far. */
> ifa_flags &= IFA_F_NODAD | IFA_F_HOMEADDRESS | IFA_F_MANAGETEMPADDR |
> - IFA_F_NOPREFIXROUTE | IFA_F_MCAUTOJOIN;
> + IFA_F_NOPREFIXROUTE | IFA_F_MCAUTOJOIN | IFA_F_OPTIMISTIC;
> +
> + if (ifa_flags & IFA_F_NODAD && ifa_flags & IFA_F_OPTIMISTIC)
> + return -EINVAL;
... add an extack message telling users nodad and optimistic are
mutually exclusive.
Also, it seems like this feature needs to be wrapped in
CONFIG_IPV6_OPTIMISTIC_DAD and optimistic checks for linklocal and
autoconf are wrapped in sysctl checks. Why shouldn't manual addresses
follow suit?
>
> ifa = ipv6_get_ifaddr(net, pfx, dev, 1);
> if (!ifa) {
>
