Keep mbuf header field ph_mss during loopback TCP with LRO/TSO.

When M_TCP_TSO is preserved, also keep ph_mss.  In lo(4) this logic
was missing.  This may be relevant only for weird pf configs that
forward from loopback.

OK mvs@ jan@

diff --git a/sys/net/if.c b/sys/net/if.c
index fd54cc8..27570be 100644 (file)
--- a/sys/net/if.c
+++ b/sys/net/if.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: if.c,v 1.705 2023/07/07 08:05:02 bluhm Exp $  */
+/*     $OpenBSD: if.c,v 1.706 2023/07/07 19:45:26 bluhm Exp $  */
 /*     $NetBSD: if.c,v 1.35 1996/05/07 05:26:04 thorpej Exp $  */
 
 /*
@@ -782,6 +782,7 @@ int
 if_input_local(struct ifnet *ifp, struct mbuf *m, sa_family_t af)
 {
        int keepflags, keepcksum;
+       uint16_t keepmss;
 
 #if NBPFILTER > 0
        /*
@@ -807,9 +808,11 @@ if_input_local(struct ifnet *ifp, struct mbuf *m, sa_family_t af)
        keepcksum = m->m_pkthdr.csum_flags & (M_IPV4_CSUM_OUT |
            M_TCP_CSUM_OUT | M_UDP_CSUM_OUT | M_ICMP_CSUM_OUT |
            M_TCP_TSO);
+       keepmss = m->m_pkthdr.ph_mss;
        m_resethdr(m);
        m->m_flags |= M_LOOP | keepflags;
        m->m_pkthdr.csum_flags = keepcksum;
+       m->m_pkthdr.ph_mss = keepmss;
        m->m_pkthdr.ph_ifidx = ifp->if_index;
        m->m_pkthdr.ph_rtableid = ifp->if_rdomain;