From b75326c201242de9495ff98e5d5cff41d7fc0d9d Mon Sep 17 00:00:00 2001 From: Fernando Gont Date: Sun, 19 Apr 2020 09:24:57 -0300 Subject: ipv6: Honor all IPv6 PIO Valid Lifetime values RFC4862 5.5.3 e) prevents received Router Advertisements from reducing the Valid Lifetime of configured addresses to less than two hours, thus preventing hosts from reacting to the information provided by a router that has positive knowledge that a prefix has become invalid. This patch makes hosts honor all Valid Lifetime values, as per draft-gont-6man-slaac-renum-06, Section 4.2. This is meant to help mitigate the problem discussed in draft-ietf-v6ops-slaac-renum. Note: Attacks aiming at disabling an advertised prefix via a Valid Lifetime of 0 are not really more harmful than other attacks that can be performed via forged RA messages, such as those aiming at completely disabling a next-hop router via an RA that advertises a Router Lifetime of 0, or performing a Denial of Service (DoS) attack by advertising illegitimate prefixes via forged PIOs. In scenarios where RA-based attacks are of concern, proper mitigations such as RA-Guard [RFC6105] [RFC7113] should be implemented. Signed-off-by: Fernando Gont Signed-off-by: David S. Miller --- net/ipv6/addrconf.c | 27 +++++++-------------------- 1 file changed, 7 insertions(+), 20 deletions(-) (limited to 'net/ipv6') diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c index 24e319dfb510..27b4fb6e452b 100644 --- a/net/ipv6/addrconf.c +++ b/net/ipv6/addrconf.c @@ -2564,7 +2564,7 @@ int addrconf_prefix_rcv_add_addr(struct net *net, struct net_device *dev, __u32 valid_lft, u32 prefered_lft) { struct inet6_ifaddr *ifp = ipv6_get_ifaddr(net, addr, dev, 1); - int create = 0, update_lft = 0; + int create = 0; if (!ifp && valid_lft) { int max_addresses = in6_dev->cnf.max_addresses; @@ -2608,32 +2608,19 @@ int addrconf_prefix_rcv_add_addr(struct net *net, struct net_device *dev, unsigned long now; u32 stored_lft; - /* update lifetime (RFC2462 5.5.3 e) */ + /* Update lifetime (RFC4862 5.5.3 e) + * We deviate from RFC4862 by honoring all Valid Lifetimes to + * improve the reaction of SLAAC to renumbering events + * (draft-gont-6man-slaac-renum-06, Section 4.2) + */ spin_lock_bh(&ifp->lock); now = jiffies; if (ifp->valid_lft > (now - ifp->tstamp) / HZ) stored_lft = ifp->valid_lft - (now - ifp->tstamp) / HZ; else stored_lft = 0; - if (!create && stored_lft) { - const u32 minimum_lft = min_t(u32, - stored_lft, MIN_VALID_LIFETIME); - valid_lft = max(valid_lft, minimum_lft); - - /* RFC4862 Section 5.5.3e: - * "Note that the preferred lifetime of the - * corresponding address is always reset to - * the Preferred Lifetime in the received - * Prefix Information option, regardless of - * whether the valid lifetime is also reset or - * ignored." - * - * So we should always update prefered_lft here. - */ - update_lft = 1; - } - if (update_lft) { + if (!create && stored_lft) { ifp->valid_lft = valid_lft; ifp->prefered_lft = prefered_lft; ifp->tstamp = now; -- cgit v1.2.3