[PATCH v2 4/9] 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 addrs[] array.

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
---
 fwd.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/fwd.c b/fwd.c
index 8d8151b..f1db34c 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)
 {
+	int i;
+
 	if (IN4_IS_ADDR_LOOPBACK(addr))
 		return false;
 
@@ -513,11 +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 (i = 0; i < c->ip4.addr_count; i++)
+		if (IN4_ARE_ADDR_EQUAL(addr, inany_v4(&c->ip4.addrs[i].addr)))
+			return false;
+
+	/* Also check addr_seen: it tracks the address the guest is actually
+	 * using, which may differ from configured addresses.
 	 */
-	if (IN4_ARE_ADDR_EQUAL(addr, inany_v4(&c->ip4.addrs[0].addr)) ||
-	    IN4_ARE_ADDR_EQUAL(addr, &c->ip4.addr_seen))
+	if (IN4_ARE_ADDR_EQUAL(addr, &c->ip4.addr_seen))
 		return false;
 
 	return true;
@@ -534,11 +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)
 {
+	int i;
+
 	if (IN6_IS_ADDR_LOOPBACK(addr))
 		return false;
 
-	if (IN6_ARE_ADDR_EQUAL(addr, &c->ip6.addrs[0].addr.a6))
-		return false;
+	/* Check against all configured guest addresses */
+	for (i = 0; i < c->ip6.addr_count; i++)
+		if (IN6_ARE_ADDR_EQUAL(addr, &c->ip6.addrs[i].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
-- 
2.52.0