[PATCH v6 09/13] ip: Track observed guest IPv6 addresses in unified address array

[Jon Maloy <jmaloy@redhat.com>]

We remove the addr_seen and addr_ll_seen fields in struct ip6_ctx
and replace them by setting CONF_ADDR_OBSERVED and CONF_ADDR_LINKLOCAL
flags in the corresponding entry in the unified address array.

The observed IPv6 address is always added/moved to position 0
in the array, improving chances for fast lookup.

This completes the unification of address storage for both IPv4 and
IPv6, enabling future support for multiple guest addresses per family.

Signed-off-by: Jon Maloy <jmaloy@redhat.com>

---
v5: - Made to use same algorithm and function as IPv4 for inserting
      observed into the array.

v6: - Re-introduced code that by accident had been moved to the
      previous commit.
    - Some fixes based on feedback from David G.
---
 conf.c    |  6 ------
 dhcpv6.c  | 20 +++++++++++--------
 dhcpv6.h  |  2 +-
 fwd.c     | 38 ++++++++++++++++++++++--------------
 inany.h   |  3 +++
 migrate.c | 33 +++++++++++++++++++++++--------
 passt.h   |  4 ----
 pasta.c   |  7 +++++--
 tap.c     | 58 ++++++++++++++++++++++++++++++++++++-------------------
 9 files changed, 107 insertions(+), 64 deletions(-)

diff --git a/conf.c b/conf.c
index 1c9f07c..320a9e4 100644
--- a/conf.c
+++ b/conf.c
@@ -767,8 +767,6 @@ static unsigned int conf_ip4(struct ctx *c, unsigned int ifi)
 		}
 		if (!rc || !fwd_get_addr(c, AF_INET, 0, 0))
 			return 0;
-
-		a = fwd_get_addr(c, AF_INET, CONF_ADDR_HOST, 0);
 	}
 
 	ip4->our_tap_addr = ip4->guest_gw;
@@ -829,7 +827,6 @@ static unsigned int conf_ip6(struct ctx *c, unsigned int ifi)
 			      strerror_(-rc));
 			return 0;
 		}
-		a = fwd_get_addr(c, AF_INET6, CONF_ADDR_HOST, 0);
 	} else {
 		rc = nl_addr_get_ll(nl_sock, ifi, &ip6->our_tap_ll);
 		if (rc < 0) {
@@ -838,9 +835,6 @@ static unsigned int conf_ip6(struct ctx *c, unsigned int ifi)
 		}
 	}
 
-	if (a)
-		ip6->addr_seen = a->addr.a6;
-
 	if (IN6_IS_ADDR_LINKLOCAL(&ip6->guest_gw))
 		ip6->our_tap_ll = ip6->guest_gw;
 
diff --git a/dhcpv6.c b/dhcpv6.c
index 3a007bf..313c243 100644
--- a/dhcpv6.c
+++ b/dhcpv6.c
@@ -382,8 +382,12 @@ static void dhcpv6_send_ia_notonlink(struct ctx *c,
 {
 	const struct in6_addr *src = &c->ip6.our_tap_ll;
 	struct opt_hdr *ia = (struct opt_hdr *)resp_not_on_link.var;
+	const struct in6_addr *dst = tap_ip6_daddr(c, src);
 	size_t n;
 
+	if (!dst)
+		return;
+
 	info("DHCPv6: received CONFIRM with inappropriate IA,"
 	     " sending NotOnLink status in REPLY");
 
@@ -405,7 +409,7 @@ static void dhcpv6_send_ia_notonlink(struct ctx *c,
 
 	resp_not_on_link.hdr.xid = xid;
 
-	tap_udp6_send(c, src, 547, tap_ip6_daddr(c, src), 546,
+	tap_udp6_send(c, src, 547, dst, 546,
 		      xid, &resp_not_on_link, n);
 }
 
@@ -549,7 +553,7 @@ static size_t dhcpv6_client_fqdn_fill(const struct iov_tail *data,
  * Return: 0 if it's not a DHCPv6 message, 1 if handled, -1 on failure
  */
 int dhcpv6(struct ctx *c, struct iov_tail *data,
-	   const struct in6_addr *saddr, const struct in6_addr *daddr)
+	   const struct in6_addr *daddr)
 {
 	const struct opt_server_id *server_id = NULL;
 	const struct opt_hdr *client_id = NULL;
@@ -565,9 +569,9 @@ int dhcpv6(struct ctx *c, struct iov_tail *data,
 	/* cppcheck-suppress [variableScope,unmatchedSuppression] */
 	struct opt_hdr client_id_storage;
 	/* cppcheck-suppress [variableScope,unmatchedSuppression] */
+	const struct in6_addr *src, *dst;
 	struct opt_ia_na ia_storage;
 	const struct guest_addr *a;
-	const struct in6_addr *src;
 	struct msg_hdr mh_storage;
 	const struct msg_hdr *mh;
 	struct udphdr uh_storage;
@@ -593,9 +597,12 @@ int dhcpv6(struct ctx *c, struct iov_tail *data,
 	if (mlen + sizeof(*uh) != ntohs(uh->len) || mlen < sizeof(*mh))
 		return -1;
 
-	c->ip6.addr_ll_seen = *saddr;
+	/* Guest LL address already recorded by tap_check_src_addr6() */
 
 	src = &c->ip6.our_tap_ll;
+	dst = tap_ip6_daddr(c, src);
+	if (!dst)
+		return -1;
 
 	mh = IOV_REMOVE_HEADER(data, mh_storage);
 	if (!mh)
@@ -683,10 +690,7 @@ int dhcpv6(struct ctx *c, struct iov_tail *data,
 
 	resp.hdr.xid = mh->xid;
 
-	tap_udp6_send(c, src, 547, tap_ip6_daddr(c, src), 546,
-		      mh->xid, &resp, n);
-	if (a)
-		c->ip6.addr_seen = a->addr.a6;
+	tap_udp6_send(c, src, 547, dst, 546, mh->xid, &resp, n);
 
 	return 1;
 }
diff --git a/dhcpv6.h b/dhcpv6.h
index c706dfd..eda133f 100644
--- a/dhcpv6.h
+++ b/dhcpv6.h
@@ -7,7 +7,7 @@
 #define DHCPV6_H
 
 int dhcpv6(struct ctx *c, struct iov_tail *data,
-	   struct in6_addr *saddr, struct in6_addr *daddr);
+	   const struct in6_addr *daddr);
 void dhcpv6_init(const struct ctx *c);
 
 #endif /* DHCPV6_H */
diff --git a/fwd.c b/fwd.c
index 28a721e..b3f5dc0 100644
--- a/fwd.c
+++ b/fwd.c
@@ -1095,14 +1095,6 @@ static bool fwd_guest_accessible(const struct ctx *c,
 		if (inany_equals(addr, &a->addr))
 			return false;
 
-	/* For IPv6, addr_seen starts unspecified, because we don't know what LL
-	 * address the guest will take until we see it.  Only check against it
-	 * if it has been set to a real address.
-	 */
-	if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr_seen) &&
-	    inany_equals6(addr, &c->ip6.addr_seen))
-		return false;
-
 	return true;
 }
 
@@ -1305,10 +1297,20 @@ uint8_t fwd_nat_from_host(const struct ctx *c,
 			}
 			tgt->oaddr = inany_any4;
 		} else {
-			if (c->host_lo_to_ns_lo)
+			if (c->host_lo_to_ns_lo) {
 				tgt->eaddr = inany_loopback6;
-			else
-				tgt->eaddr.a6 = c->ip6.addr_seen;
+			} else {
+				const struct guest_addr *a;
+
+				a = fwd_select_addr(c, AF_INET6,
+						    CONF_ADDR_OBSERVED,
+						    CONF_ADDR_USER |
+						    CONF_ADDR_HOST,
+						    CONF_ADDR_LINKLOCAL);
+				if (!a)
+					return PIF_NONE;
+				tgt->eaddr = a->addr;
+			}
 			tgt->oaddr = inany_any6;
 		}
 
@@ -1346,10 +1348,16 @@ uint8_t fwd_nat_from_host(const struct ctx *c,
 
 		tgt->eaddr = a->addr;
 	} else {
-		if (inany_is_linklocal6(&tgt->oaddr))
-			tgt->eaddr.a6 = c->ip6.addr_ll_seen;
-		else
-			tgt->eaddr.a6 = c->ip6.addr_seen;
+		bool linklocal = inany_is_linklocal6(&tgt->oaddr);
+		int excl = linklocal ? 0 : CONF_ADDR_LINKLOCAL;
+		const struct guest_addr *a;
+
+		a = fwd_select_addr(c, AF_INET6, CONF_ADDR_OBSERVED,
+				    CONF_ADDR_USER | CONF_ADDR_HOST, excl);
+		if (!a)
+			return PIF_NONE;
+
+		tgt->eaddr = a->addr;
 	}
 
 	return PIF_TAP;
diff --git a/inany.h b/inany.h
index 7b23cb0..82dd102 100644
--- a/inany.h
+++ b/inany.h
@@ -60,6 +60,9 @@ extern const union inany_addr inany_any4;
 #define inany_from_v4(a4)	\
 	((union inany_addr)INANY_INIT4((a4)))
 
+#define inany_from_v6(v6)	\
+	((union inany_addr){ .a6 = (v6) })
+
 /** union sockaddr_inany - Either a sockaddr_in or a sockaddr_in6
  * @sa_family:	Address family, AF_INET or AF_INET6
  * @sa:		Plain struct sockaddr (useful to avoid casts)
diff --git a/migrate.c b/migrate.c
index 1e02720..a92301b 100644
--- a/migrate.c
+++ b/migrate.c
@@ -56,21 +56,30 @@ struct migrate_seen_addrs_v2 {
 static int seen_addrs_source_v2(struct ctx *c,
 				const struct migrate_stage *stage, int fd)
 {
-	struct migrate_seen_addrs_v2 addrs = {
-		.addr6 = c->ip6.addr_seen,
-		.addr6_ll = c->ip6.addr_ll_seen,
-	};
+	struct migrate_seen_addrs_v2 addrs = { 0 };
 	const struct guest_addr *a;
 
 	(void)stage;
 
-	/* IPv4 observed address, with fallback to configured address */
+	/* IPv4 observed address, with fallback to any other non-LL address */
 	a = fwd_select_addr(c, AF_INET, CONF_ADDR_OBSERVED,
 			    CONF_ADDR_USER | CONF_ADDR_HOST,
 			    CONF_ADDR_LINKLOCAL);
 	if (a)
 		addrs.addr4 = *inany_v4(&a->addr);
 
+	/* IPv6 observed address, with fallback to any other non-LL address */
+	a = fwd_select_addr(c, AF_INET6, CONF_ADDR_OBSERVED,
+			    CONF_ADDR_USER | CONF_ADDR_HOST,
+			    CONF_ADDR_LINKLOCAL);
+	if (a)
+		addrs.addr6 = a->addr.a6;
+
+	/* IPv6 link-local address */
+	a = fwd_get_addr(c, AF_INET6, CONF_ADDR_LINKLOCAL, 0);
+	if (a)
+		addrs.addr6_ll = a->addr.a6;
+
 	memcpy(addrs.mac, c->guest_mac, sizeof(addrs.mac));
 
 	if (write_all_buf(fd, &addrs, sizeof(addrs)))
@@ -91,19 +100,27 @@ static int seen_addrs_target_v2(struct ctx *c,
 				const struct migrate_stage *stage, int fd)
 {
 	struct migrate_seen_addrs_v2 addrs;
+	struct in6_addr addr6, addr6_ll;
 
 	(void)stage;
 
 	if (read_all_buf(fd, &addrs, sizeof(addrs)))
 		return errno;
 
-	c->ip6.addr_seen = addrs.addr6;
-	c->ip6.addr_ll_seen = addrs.addr6_ll;
-
 	if (addrs.addr4.s_addr)
 		fwd_set_addr(c, &inany_from_v4(addrs.addr4),
 			     CONF_ADDR_OBSERVED, 0);
 
+	addr6 = addrs.addr6;
+	if (!IN6_IS_ADDR_UNSPECIFIED(&addr6))
+		fwd_set_addr(c, &inany_from_v6(addr6),
+			     CONF_ADDR_OBSERVED, 0);
+
+	addr6_ll = addrs.addr6_ll;
+	if (!IN6_IS_ADDR_UNSPECIFIED(&addr6_ll))
+		fwd_set_addr(c, &inany_from_v6(addr6_ll),
+			     CONF_ADDR_OBSERVED | CONF_ADDR_LINKLOCAL, 0);
+
 	memcpy(c->guest_mac, addrs.mac, sizeof(c->guest_mac));
 
 	return 0;
diff --git a/passt.h b/passt.h
index 5452225..db2f10d 100644
--- a/passt.h
+++ b/passt.h
@@ -124,8 +124,6 @@ struct ip4_ctx {
 
 /**
  * struct ip6_ctx - IPv6 execution context
- * @addr_seen:		Latest IPv6 global/site address seen as source from tap
- * @addr_ll_seen:	Latest IPv6 link-local address seen as source from tap
  * @guest_gw:		IPv6 gateway as seen by the guest
  * @map_host_loopback:	Outbound connections to this address are NATted to the
  *                      host's [::1]
@@ -141,8 +139,6 @@ struct ip4_ctx {
  * @no_copy_addrs:	Don't copy all addresses when configuring namespace
  */
 struct ip6_ctx {
-	struct in6_addr addr_seen;
-	struct in6_addr addr_ll_seen;
 	struct in6_addr guest_gw;
 	struct in6_addr map_host_loopback;
 	struct in6_addr map_guest_addr;
diff --git a/pasta.c b/pasta.c
index b8d7cf4..fcb169a 100644
--- a/pasta.c
+++ b/pasta.c
@@ -370,6 +370,7 @@ static int pasta_conf_routes(struct ctx *c, sa_family_t af, int ifi,
 void pasta_ns_conf(struct ctx *c)
 {
 	unsigned int flags = IFF_UP;
+	struct in6_addr addr_ll;
 	int rc;
 
 	rc = nl_link_set_flags(nl_sock_ns, 1 /* lo */, IFF_UP, IFF_UP);
@@ -417,11 +418,13 @@ void pasta_ns_conf(struct ctx *c)
 	if (!c->ifi6)
 		goto done;
 
-	rc = nl_addr_get_ll(nl_sock_ns, c->pasta_ifi,
-			    &c->ip6.addr_ll_seen);
+	rc = nl_addr_get_ll(nl_sock_ns, c->pasta_ifi, &addr_ll);
 	if (rc < 0)
 		warn("Can't get LL address from namespace: %s",
 		     strerror_(-rc));
+	else
+		fwd_set_addr(c, &inany_from_v6(addr_ll),
+			     CONF_ADDR_LINKLOCAL | CONF_ADDR_HOST, 0);
 
 	rc = nl_addr_set_ll_nodad(nl_sock_ns, c->pasta_ifi);
 	if (rc < 0)
diff --git a/tap.c b/tap.c
index c75a4df..07f92bb 100644
--- a/tap.c
+++ b/tap.c
@@ -173,19 +173,51 @@ static void tap_check_src_addr4(struct ctx *c, const struct in_addr *addr)
 		fwd_set_addr(c, &inany_from_v4(*addr), CONF_ADDR_OBSERVED, 0);
 }
 
+/**
+ * tap_check_src_addr6() - Note an IPv6 address seen in guest traffic
+ * @c:		Execution context
+ * @addr:	IPv6 address seen as source from guest
+ */
+static void tap_check_src_addr6(struct ctx *c, const struct in6_addr *addr)
+{
+	uint8_t flags = CONF_ADDR_OBSERVED;
+
+	if (IN6_IS_ADDR_UNSPECIFIED(addr))
+		return;
+
+	if (IN6_IS_ADDR_LINKLOCAL(addr))
+		flags |= CONF_ADDR_LINKLOCAL;
+
+	fwd_set_addr(c, &inany_from_v6(*addr), flags, 0);
+}
+
 /**
  * tap_ip6_daddr() - Normal IPv6 destination address for inbound packets
  * @c:		Execution context
  * @src:	Source address
  *
- * Return: pointer to IPv6 address
+ * Return: pointer to IPv6 address, NULL if no suitable address found
  */
 const struct in6_addr *tap_ip6_daddr(const struct ctx *c,
 				     const struct in6_addr *src)
 {
-	if (IN6_IS_ADDR_LINKLOCAL(src))
-		return &c->ip6.addr_ll_seen;
-	return &c->ip6.addr_seen;
+	const struct guest_addr *a;
+
+	if (IN6_IS_ADDR_LINKLOCAL(src)) {
+		/* Link-local: first LL address in array */
+		a = fwd_get_addr(c, AF_INET6, CONF_ADDR_LINKLOCAL, 0);
+	} else {
+		/* Global: observed non-LL first, then any non-LL */
+		a = fwd_select_addr(c, AF_INET6, CONF_ADDR_OBSERVED,
+				    CONF_ADDR_USER | CONF_ADDR_HOST,
+				    CONF_ADDR_LINKLOCAL);
+	}
+
+	if (a)
+		return &a->addr.a6;
+
+	debug("No suitable IPv6 guest address found");
+	return NULL;
 }
 
 /**
@@ -958,21 +990,7 @@ resume:
 			continue;
 		}
 
-		if (IN6_IS_ADDR_LINKLOCAL(saddr)) {
-			c->ip6.addr_ll_seen = *saddr;
-
-			if (IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr_seen)) {
-				c->ip6.addr_seen = *saddr;
-			}
-
-			if (!fwd_get_addr(c, AF_INET6, 0, 0)) {
-				union inany_addr addr = { .a6 = *saddr };
-
-				fwd_set_addr(c, &addr, CONF_ADDR_LINKLOCAL, 64);
-			}
-		} else if (!IN6_IS_ADDR_UNSPECIFIED(saddr)){
-			c->ip6.addr_seen = *saddr;
-		}
+		tap_check_src_addr6(c, saddr);
 
 		if (proto == IPPROTO_ICMPV6) {
 			struct iov_tail ndp_data;
@@ -1003,7 +1021,7 @@ resume:
 		if (proto == IPPROTO_UDP) {
 			struct iov_tail uh_data = data;
 
-			if (dhcpv6(c, &uh_data, saddr, daddr))
+			if (dhcpv6(c, &uh_data, daddr))
 				continue;
 		}
 
-- 
2.52.0