[PATCH v3 04/11] fwd: Check all configured addresses in guest accessibility functions

[Jon Maloy <jmaloy@redhat.com>]

As a preparation for handling multiple addresses, we update
fwd_guest_accessible4() and fwd_guest_accessible6() to check
against all addresses in the unified addrs[] array using the
for_each_addr() macro.

This ensures that when multiple addresses are configured via -a options,
inbound traffic for any of them is correctly detected as having no valid
forwarding path, and subsequently dropped. This occurs when a peer
address collides with an address the guest is using, and we have no
translation for it.

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

---
v2: Updated commit log to make it clearer
v3: Adapted to changes earlier in the series
---
 fwd.c | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/fwd.c b/fwd.c
index 54248a3..20d581d 100644
--- a/fwd.c
+++ b/fwd.c
@@ -502,6 +502,8 @@ static bool is_dns_flow(uint8_t proto, const struct flowside *ini)
 static bool fwd_guest_accessible4(const struct ctx *c,
 				    const struct in_addr *addr)
 {
+	const struct inany_addr_entry *e;
+
 	if (IN4_IS_ADDR_LOOPBACK(addr))
 		return false;
 
@@ -513,12 +515,15 @@ static bool fwd_guest_accessible4(const struct ctx *c,
 	if (IN4_IS_ADDR_UNSPECIFIED(addr))
 		return false;
 
-	/* For IPv4, addr_seen is initialised to addr, so is always a valid
-	 * address
+	/* Check against all configured guest addresses */
+	for_each_addr(c, e, AF_INET)
+		if (IN4_ARE_ADDR_EQUAL(addr, inany_v4(&e->addr)))
+			return false;
+
+	/* Also check addr_seen: it tracks the address the guest is actually
+	 * using, which may differ from configured addresses.
 	 */
-	if ((first_v4(c) &&
-	     IN4_ARE_ADDR_EQUAL(addr, inany_v4(&first_v4(c)->addr))) ||
-	    IN4_ARE_ADDR_EQUAL(addr, &c->ip4.addr_seen))
+	if (IN4_ARE_ADDR_EQUAL(addr, &c->ip4.addr_seen))
 		return false;
 
 	return true;
@@ -535,11 +540,15 @@ static bool fwd_guest_accessible4(const struct ctx *c,
 static bool fwd_guest_accessible6(const struct ctx *c,
 				  const struct in6_addr *addr)
 {
+	const struct inany_addr_entry *e;
+
 	if (IN6_IS_ADDR_LOOPBACK(addr))
 		return false;
 
-	if (first_v6(c) && IN6_ARE_ADDR_EQUAL(addr, &first_v6(c)->addr.a6))
-		return false;
+	/* Check against all configured guest addresses */
+	for_each_addr(c, e, AF_INET6)
+		if (IN6_ARE_ADDR_EQUAL(addr, &e->addr.a6))
+			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
@@ -714,7 +723,7 @@ bool nat_inbound(const struct ctx *c, const union inany_addr *addr,
 		   first_v4(c) && inany_equals(addr, &first_v4(c)->addr)) {
 		*translated = inany_from_v4(c->ip4.map_guest_addr);
 	} else if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.map_guest_addr) &&
-		   first_v6(c) && inany_equals6(addr, &first_v6(c)->addr.a6)) {
+		   first_v6(c) && inany_equals(addr, &first_v6(c)->addr)) {
 		translated->a6 = c->ip6.map_guest_addr;
 	} else if (fwd_guest_accessible(c, addr)) {
 		*translated = *addr;
-- 
2.52.0