[PATCH 1/2 net v4] ipv6: addrconf: fix temp address generation after prefix deprecation

[Fernando Fernandez Mancera <fmancera@suse.de>]

When a router temporarily deprecates an IPv6 prefix (either by sending a
Router Advertisement with Preferred Lifetime = 0 or by letting the
lifetime expire) and later restores it, the kernel permanently loses its
ability to generate temporary privacy addresses (RFC 8981) for that
prefix.

This happens because the address worker attempts to generate a
replacement temporary address when the current one nears expiration. As
the base prefix is deprecated already, the generation fails after
marking the temporary address as already having spawned a replacement
(ifp->regen_count++).

When the router eventually restores the prefix, the temporary address
becomes active again. However, once it naturally expires, the address
worker sees this temporary address already tried to generate one and
skips the regeneration.

Fix this by checking if all temporary addresses for a given prefix have
already tried to spawn a replacement when processing a new RA. If so,
spawn a new temporary address.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: Łukasz Stelmach <steelman@post.pl>
Closes: https://lore.kernel.org/netdev/87340td30q.fsf%25steelman@post.pl/
Suggested-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
---
v2: adjusted commit message, adjusted the implementation to cover all
race conditions
v3: regen now if ipv6_create_tempaddr failed due to timer to avoid an
infinite loop as we restart the loop and we need to check now against
prefered_lft again.
v4: change the proposed fix completely, now we address the problem when
doing manage_tempaddrs().
---
 net/ipv6/addrconf.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 5476b6536eb7..18a6f2de30ce 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -2595,8 +2595,9 @@ static void manage_tempaddrs(struct inet6_dev *idev,
 			     __u32 valid_lft, __u32 prefered_lft,
 			     bool create, unsigned long now)
 {
-	u32 flags;
 	struct inet6_ifaddr *ift;
+	bool all_regen = true;
+	u32 flags;
 
 	read_lock_bh(&idev->lock);
 	/* update all temporary addresses in the list */
@@ -2637,6 +2638,8 @@ static void manage_tempaddrs(struct inet6_dev *idev,
 		ift->tstamp = now;
 		if (prefered_lft > 0)
 			ift->flags &= ~IFA_F_DEPRECATED;
+		if (!ift->regen_count)
+			all_regen = false;
 
 		spin_unlock(&ift->lock);
 		if (!(flags&IFA_F_TENTATIVE))
@@ -2644,12 +2647,14 @@ static void manage_tempaddrs(struct inet6_dev *idev,
 	}
 
 	/* Also create a temporary address if it's enabled but no temporary
-	 * address currently exists.
+	 * address currently exists or if all temporary addresses already
+	 * generated an address.
 	 * However, we get called with valid_lft == 0, prefered_lft == 0, create == false
 	 * as part of cleanup (ie. deleting the mngtmpaddr).
 	 * We don't want that to result in creating a new temporary ip address.
 	 */
-	if (list_empty(&idev->tempaddr_list) && (valid_lft || prefered_lft))
+	if ((list_empty(&idev->tempaddr_list) || all_regen) &&
+	    (valid_lft || prefered_lft))
 		create = true;
 
 	if (create && READ_ONCE(idev->cnf.use_tempaddr) > 0) {
-- 
2.53.0