[PATCH net v4 3/4] ipv6: initialize temporary ifaddr before publication

[Daehyeon Ko <4ncienth@gmail.com>]

ipv6_create_tempaddr() holds a reference to the public ifaddr, publishes
the new temporary address through ipv6_add_addr(), and only then stores
the reference and final timestamps.

addrconf_ifdown() can remove the temporary address before ifpub is
stored, leaking the public ifaddr reference. Publishing ifpub alone is
insufficient: manage_tempaddrs() can then find the object before cstamp
and tstamp are final, update its lifetimes, and have the constructor
overwrite its timestamp with an older value.

This follow-on was found by source review and was not separately
triggered at runtime.

Pass the public ifaddr and both timestamps in ifa6_config. Initialize all
three fields before adding the temporary address to either the hash or
per-device lists. On success the existing public-ifaddr reference
transfers to the temporary object. On error it remains owned and released
by ipv6_create_tempaddr().

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Reported-by: Sashiko <netdev-bot+sashiko@kernel.org>
Closes: https://lore.kernel.org/r/179122559913.434549.12720841717630168470@kernel.org
Link: https://lore.kernel.org/r/179161099665.434549.5858601179492551889@kernel.org
Link: https://lore.kernel.org/r/20261007164548.GA1153540@shredder
Link: https://lore.kernel.org/r/20261012145240.GA779501@shredder
Suggested-by: Ido Schimmel <idosch@nvidia.com>
Assisted-by: LLM
Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
---
 include/net/addrconf.h |  3 +++
 net/ipv6/addrconf.c    | 20 +++++++++++++-------
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/include/net/addrconf.h b/include/net/addrconf.h
index e6764245995f25..6818057cf72750 100644
--- a/include/net/addrconf.h
+++ b/include/net/addrconf.h
@@ -81,6 +81,9 @@ struct ifa6_config {
 	u8			ifa_proto;
 
 	const struct in6_addr	*peer_pfx;
+	struct inet6_ifaddr	*ifpub;
+	unsigned long		cstamp;
+	unsigned long		tstamp;
 
 	u32			rt_priority;
 	u32			ifa_flags;
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 3bede30d4e989b..df566681226195 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -1155,10 +1155,19 @@ ipv6_add_addr(struct inet6_dev *idev, struct ifa6_config *cfg,
 		ifa->flags |= IFA_F_TENTATIVE;
 	ifa->valid_lft = cfg->valid_lft;
 	ifa->prefered_lft = cfg->preferred_lft;
-	ifa->cstamp = ifa->tstamp = jiffies;
 	ifa->tokenized = false;
 
 	ifa->rt = f6i;
+	ifa->ifpub = cfg->ifpub;
+	if (cfg->ifpub) {
+		ifa->cstamp = cfg->cstamp;
+		ifa->tstamp = cfg->tstamp;
+	} else {
+		unsigned long now = jiffies;
+
+		ifa->cstamp = now;
+		ifa->tstamp = now;
+	}
 
 	ifa->idev = idev;
 	in6_dev_hold(idev);
@@ -1491,6 +1500,9 @@ static int ipv6_create_tempaddr(struct inet6_ifaddr *ifp, bool block)
 
 	cfg.pfx = &addr;
 	cfg.scope = ipv6_addr_scope(cfg.pfx);
+	cfg.ifpub = ifp;
+	cfg.cstamp = now;
+	cfg.tstamp = tmp_tstamp;
 
 	ift = ipv6_add_addr(idev, &cfg, block, NULL);
 	if (IS_ERR(ift)) {
@@ -1501,12 +1513,6 @@ static int ipv6_create_tempaddr(struct inet6_ifaddr *ifp, bool block)
 		goto retry;
 	}
 
-	spin_lock_bh(&ift->lock);
-	ift->ifpub = ifp;
-	ift->cstamp = now;
-	ift->tstamp = tmp_tstamp;
-	spin_unlock_bh(&ift->lock);
-
 	addrconf_dad_start(ift);
 	in6_ifa_put(ift);
 	in6_dev_put(idev);
-- 
2.55.0