Patch "ipv6: dad: don't remove dynamic addresses if link is down" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

ipv6: dad: don't remove dynamic addresses if link is down

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ipv6-dad-don-t-remove-dynamic-addresses-if-link-is-down.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Sabrina Dubroca <[email protected]>
Date: Thu, 29 Jun 2017 16:56:54 +0200
Subject: ipv6: dad: don't remove dynamic addresses if link is down

From: Sabrina Dubroca <[email protected]>

commit ec8add2a4c9df723c94a863b8fcd6d93c472deed upstream.

Currently, when the link for $DEV is down, this command succeeds but the address is removed immediately by DAD (1):

    ip addr add 1111::12/64 dev $DEV valid_lft 3600 preferred_lft 1800

In the same situation, this will succeed and not remove the address (2):

    ip addr add 1111::12/64 dev $DEV
    ip addr change 1111::12/64 dev $DEV valid_lft 3600 preferred_lft 1800

The comment in addrconf_dad_begin() when !IF_READY makes it look like this is the intended behavior, but doesn't explain why:

* If the device is not ready:
* - keep it tentative if it is a permanent address.
* - otherwise, kill it.

We clearly cannot prevent userspace from doing (2), but we can make (1) work consistently with (2).

addrconf_dad_stop() is only called in two cases: if DAD failed, or to skip DAD when the link is down. In that second case, the fix is to avoid deleting the address, like we already do for permanent addresses.

---
 net/ipv6/addrconf.c |   18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

@@ -1875,15 +1875,7 @@ static void addrconf_dad_stop(struct ine
 	if (dad_failed)
 		ifp->flags |= IFA_F_DADFAILED;
 
-	if (ifp->flags&IFA_F_PERMANENT) {
-		spin_lock_bh(&ifp->lock);
-		addrconf_del_dad_work(ifp);
-		ifp->flags |= IFA_F_TENTATIVE;
-		spin_unlock_bh(&ifp->lock);
-		if (dad_failed)
-			ipv6_ifa_notify(0, ifp);
-		in6_ifa_put(ifp);
-	} else if (ifp->flags&IFA_F_TEMPORARY) {
+	if (ifp->flags&IFA_F_TEMPORARY) {
 		struct inet6_ifaddr *ifpub;
 		spin_lock_bh(&ifp->lock);
 		ifpub = ifp->ifpub;

@@ -1896,6 +1888,14 @@ static void addrconf_dad_stop(struct ine
 			spin_unlock_bh(&ifp->lock);
 		}
 		ipv6_del_addr(ifp);
+	} else if (ifp->flags&IFA_F_PERMANENT || !dad_failed) {
+		spin_lock_bh(&ifp->lock);
+		addrconf_del_dad_work(ifp);
+		ifp->flags |= IFA_F_TENTATIVE;
+		spin_unlock_bh(&ifp->lock);
+		if (dad_failed)
+			ipv6_ifa_notify(0, ifp);
+		in6_ifa_put(ifp);
 	} else {
 		ipv6_del_addr(ifp);
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/ipv6-dad-don-t-remove-dynamic-addresses-if-link-is-down.patch