pif: Correctly set scope_id for guest-side link local addressesHEAD2025_12_10.d04c480master

pif_sockaddr() is supposed to generate a suitable socket address, either
for the host, or for the guest, depending on the 'pif' parameter.  When
given a link-local address, this means it needs to generate a suitable
scope_id to specify which link.  It does this for the host, but not for the
guest.

I think this was done on the assumption that we won't ever generate guest
side link local addresses when forwarding connections.  That, however, is
not the case, at least with the recent extensions to "local mode".  Fix the
problem by properly populating the scope_id field for guest addresses.

Link: https://bugs.passt.top/show_bug.cgi?id=181
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 7 insertions, 3 deletions

diff --git a/pif.c b/pif.c
index 3d7a90e..6ae970a 100644
--- a/pif.c
+++ b/pif.c
@@ -50,10 +50,14 @@ void pif_sockaddr(const struct ctx *c, union sockaddr_inany *sa,
 		sa->sa_family = AF_INET6;
 		sa->sa6.sin6_addr = addr->a6;
 		sa->sa6.sin6_port = htons(port);
-		if (pif == PIF_HOST && IN6_IS_ADDR_LINKLOCAL(&addr->a6))
-			sa->sa6.sin6_scope_id = c->ifi6;
-		else
+		if (IN6_IS_ADDR_LINKLOCAL(&addr->a6)) {
+			if (pif == PIF_HOST)
+				sa->sa6.sin6_scope_id = c->ifi6;
+			else if (pif == PIF_SPLICE)
+				sa->sa6.sin6_scope_id = c->pasta_ifi;
+		} else {
 			sa->sa6.sin6_scope_id = 0;
+		}
 		sa->sa6.sin6_flowinfo = 0;
 	}
 }