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ipv6: Honor all IPv6 PIO Valid Lifetime values

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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 <fgont@si6networks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Fernando Gont 2020-04-19 09:24:57 -03:00 committed by David S. Miller
parent 30685b2a43
commit b75326c201
2 changed files with 7 additions and 22 deletions
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2
include/net/addrconf.h
View File

@ -6,8 +6,6 @@
#define RTR_SOLICITATION_INTERVAL (4*HZ)
#define RTR_SOLICITATION_MAX_INTERVAL (3600*HZ) /* 1 hour */
#define MIN_VALID_LIFETIME (2*3600) /* 2 hours */
#define TEMP_VALID_LIFETIME (7*86400)
#define TEMP_PREFERRED_LIFETIME (86400)
#define REGEN_MAX_RETRY (3)

27
net/ipv6/addrconf.c
View File

@ -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) {
ifp->valid_lft = valid_lft;
ifp->prefered_lft = prefered_lft;
ifp->tstamp = now;