From f15be719b370ab694b933ab7ceb7fc3481687284 Mon Sep 17 00:00:00 2001 From: David Gibson Date: Wed, 28 Feb 2024 22:25:18 +1100 Subject: tap: Disallow loopback addresses on tap interface The "tap" interface, whether it's actually a tuntap device or a qemu socket, presents a virtual external link between different network hosts. Hence, loopback addresses make no sense there. However, nothing prevents the guest from putting bogus packets with loopback addresses onto the interface and it's not entirely clear what effect that will have on passt. Explicitly test for such packets and drop them. Signed-off-by: David Gibson Signed-off-by: Stefano Brivio --- tap.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/tap.c b/tap.c index 8a9a68b..3a66621 100644 --- a/tap.c +++ b/tap.c @@ -610,6 +610,16 @@ resume: l4_len = htons(iph->tot_len) - hlen; + if (IN4_IS_ADDR_LOOPBACK(&iph->saddr) || + IN4_IS_ADDR_LOOPBACK(&iph->daddr)) { + char sstr[INET_ADDRSTRLEN], dstr[INET_ADDRSTRLEN]; + + debug("Loopback address on tap interface: %s -> %s", + inet_ntop(AF_INET, &iph->saddr, sstr, sizeof(sstr)), + inet_ntop(AF_INET, &iph->daddr, dstr, sizeof(dstr))); + continue; + } + if (iph->saddr && c->ip4.addr_seen.s_addr != iph->saddr) c->ip4.addr_seen.s_addr = iph->saddr; @@ -766,6 +776,15 @@ resume: if (!(l4h = ipv6_l4hdr(in, i, sizeof(*eh), &proto, &l4_len))) continue; + if (IN6_IS_ADDR_LOOPBACK(saddr) || IN6_IS_ADDR_LOOPBACK(daddr)) { + char sstr[INET6_ADDRSTRLEN], dstr[INET6_ADDRSTRLEN]; + + debug("Loopback address on tap interface: %s -> %s", + inet_ntop(AF_INET6, saddr, sstr, sizeof(sstr)), + inet_ntop(AF_INET6, daddr, dstr, sizeof(dstr))); + continue; + } + if (IN6_IS_ADDR_LINKLOCAL(saddr)) { c->ip6.addr_ll_seen = *saddr; -- cgit v1.2.3