netdev - [PATCH net-next] ipv6: allow userspace to add IFA_F

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Message-Id: <a08e25eade895479e77c9a632a16ed17f7416597.1519144861.git.sd@queasysnail.net>
Date:   Tue, 20 Feb 2018 17:43:47 +0100
From:   Sabrina Dubroca <sd@...asysnail.net>
To:     netdev@...r.kernel.org
Cc:     Sabrina Dubroca <sd@...asysnail.net>
Subject: [PATCH net-next] ipv6: allow userspace to add IFA_F_OPTIMISTIC addresses

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.

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 <sd@...asysnail.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;
 
 	ifa = ipv6_get_ifaddr(net, pfx, dev, 1);
 	if (!ifa) {
-- 
2.16.1