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KRT: Fix IPv6 ECMP handling with Linux 4.11+

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Starting from Linux 4.11, IPv6 ECMP routes are now notified using
RTA_MULTIPATH, like IPv4 ones. The patch adds support for RTA_MULTIPATH
parsing for IPv6 routes. This also enables to parse ECMP alien routes
correctly.

Thanks to Vincent Bernat for the original patch.
This commit is contained in:
Ondrej Zajicek (work) 2017-09-05 00:02:20 +02:00
parent 9befc7cc4f
commit 98bb80a243
1 changed files with 42 additions and 13 deletions
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55
sysdep/linux/netlink.c
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@ -59,22 +59,26 @@
/*
* Structure nl_parse_state keeps state of received route processing. Ideally,
* we could just independently parse received Netlink messages and immediately
* propagate received routes to the rest of BIRD, but Linux kernel represents
* and announces IPv6 ECMP routes not as one route with multiple next hops (like
* RTA_MULTIPATH in IPv4 ECMP), but as a set of routes with the same prefix.
* propagate received routes to the rest of BIRD, but older Linux kernel (before
* version 4.11) represents and announces IPv6 ECMP routes not as one route with
* multiple next hops (like RTA_MULTIPATH in IPv4 ECMP), but as a sequence of
* routes with the same prefix. More recent kernels work as with IPv4.
*
* Therefore, BIRD keeps currently processed route in nl_parse_state structure
* and postpones its propagation until we expect it to be final; i.e., when
* non-matching route is received or when the scan ends. When another matching
* route is received, it is merged with the already processed route to form an
* ECMP route. Note that merging is done only for IPv6 (merge == 1), but the
* postponing is done in both cases (for simplicity). All IPv4 routes are just
* considered non-matching.
* postponing is done in both cases (for simplicity). All IPv4 routes or IPv6
* routes with RTA_MULTIPATH set are just considered non-matching.
*
* This is ignored for asynchronous notifications (every notification is handled
* as a separate route). It is not an issue for our routes, as we ignore such
* notifications anyways. But importing alien IPv6 ECMP routes does not work
* properly.
* properly with older kernels.
*
* Whatever the kernel version is, IPv6 ECMP routes are sent as multiple routes
* for the same prefix.
*/
struct nl_parse_state
@ -320,9 +324,15 @@ static struct nl_want_attrs ifa_attr_want6[BIRD_IFA_MAX] = {
#define BIRD_RTA_MAX (RTA_TABLE+1)
#ifndef IPV6
static struct nl_want_attrs mpnh_attr_want4[BIRD_RTA_MAX] = {
[RTA_GATEWAY] = { 1, 1, sizeof(ip4_addr) },
};
#else
static struct nl_want_attrs mpnh_attr_want6[BIRD_RTA_MAX] = {
[RTA_GATEWAY] = { 1, 1, sizeof(ip6_addr) },
};
#endif
#ifndef IPV6
static struct nl_want_attrs rtm_attr_want4[BIRD_RTA_MAX] = {
@ -345,6 +355,7 @@ static struct nl_want_attrs rtm_attr_want6[BIRD_RTA_MAX] = {
[RTA_PRIORITY] = { 1, 1, sizeof(u32) },
[RTA_PREFSRC] = { 1, 1, sizeof(ip6_addr) },
[RTA_METRICS] = { 1, 0, 0 },
[RTA_MULTIPATH] = { 1, 0, 0 },
[RTA_FLOW] = { 1, 1, sizeof(u32) },
[RTA_TABLE] = { 1, 1, sizeof(u32) },
};
@ -477,7 +488,7 @@ nl_add_multipath(struct nlmsghdr *h, unsigned bufsize, struct mpnh *nh)
}
static struct mpnh *
nl_parse_multipath(struct krt_proto *p, struct rtattr *ra)
nl_parse_multipath(struct krt_proto *p, struct rtattr *ra, int af)
{
/* Temporary buffer for multicast nexthops */
static struct mpnh *nh_buffer;
@ -515,10 +526,26 @@ nl_parse_multipath(struct krt_proto *p, struct rtattr *ra)
/* Nonexistent RTNH_PAYLOAD ?? */
nl_attr_len = nh->rtnh_len - RTNH_LENGTH(0);
nl_parse_attrs(RTNH_DATA(nh), mpnh_attr_want4, a, sizeof(a));
switch (af)
{
#ifndef IPV6
case AF_INET:
if (!nl_parse_attrs(RTNH_DATA(nh), mpnh_attr_want4, a, sizeof(a)))
return NULL;
break;
#else
case AF_INET6:
if (!nl_parse_attrs(RTNH_DATA(nh), mpnh_attr_want6, a, sizeof(a)))
return NULL;
break;
#endif
default:
return NULL;
}
if (a[RTA_GATEWAY])
{
memcpy(&rv->gw, RTA_DATA(a[RTA_GATEWAY]), sizeof(ip_addr));
memcpy(&rv->gw, RTA_DATA(a[RTA_GATEWAY]), sizeof(rv->gw));
ipa_ntoh(rv->gw);
neighbor *ng = neigh_find2(&p->p, &rv->gw, rv->iface,
@ -1240,10 +1267,10 @@ nl_parse_route(struct nl_parse_state *s, struct nlmsghdr *h)
{
case RTN_UNICAST:
if (a[RTA_MULTIPATH] && (i->rtm_family == AF_INET))
if (a[RTA_MULTIPATH])
{
ra->dest = RTD_MULTIPATH;
ra->nexthops = nl_parse_multipath(p, a[RTA_MULTIPATH]);
ra->nexthops = nl_parse_multipath(p, a[RTA_MULTIPATH], i->rtm_family);
if (!ra->nexthops)
{
log(L_ERR "KRT: Received strange multipath route %I/%d",
@ -1385,8 +1412,10 @@ nl_parse_route(struct nl_parse_state *s, struct nlmsghdr *h)
/*
* Ideally, now we would send the received route to the rest of kernel code.
* But IPv6 ECMP routes are sent as a sequence of routes, so we postpone it
* and merge next hops until the end of the sequence.
* But IPv6 ECMP routes before 4.11 are sent as a sequence of routes, so we
* postpone it and merge next hops until the end of the sequence. Note that
* proper multipath updates are rejected by nl_mergable_route(), so it is
* always the first case for them.
*/
if (!s->net)