KRT: Fix IPv6 ECMP handling with Linux 4.11+ (98bb80a2) · Commits · 戴 / Bird

sysdep/linux/netlink.c

+42 −13

Original line number	Diff line number	Diff line
		@@ -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)

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