Index: tcp_input.c
===================================================================
RCS file: /cvsroot/src/sys/netinet/tcp_input.c,v
retrieving revision 1.357.4.3
diff -u -p -u -r1.357.4.3 tcp_input.c
--- tcp_input.c	30 Mar 2018 11:17:19 -0000	1.357.4.3
+++ tcp_input.c	7 Jul 2020 11:28:09 -0000
@@ -1273,16 +1273,32 @@ tcp_input(struct mbuf *m, ...)
 #endif
 
 	/*
+	 * Enforce alignment requirements that are violated in
+	 * some cases, see kern/50766 for details.
+	 */
+	if (TCP_HDR_ALIGNED_P(th) == 0) {
+		m = m_copyup(m, toff + sizeof(struct tcphdr), 0);
+		if (m == NULL) {
+			TCP_STATINC(TCP_STAT_RCVSHORT);
+			return;
+		}
+		th = (struct tcphdr *)(mtod(m, char *) + toff);
+	}
+	KASSERT(TCP_HDR_ALIGNED_P(th));
+
+	/*
 	 * Get IP and TCP header.
 	 * Note: IP leaves IP header in first mbuf.
 	 */
+#ifdef INET6
+	ip6 = mtod(m, struct ip6_hdr *);
+#endif
+#ifdef INET
 	ip = mtod(m, struct ip *);
+#endif
 	switch (ip->ip_v) {
 #ifdef INET
 	case 4:
-#ifdef INET6
-		ip6 = NULL;
-#endif
 		af = AF_INET;
 		iphlen = sizeof(struct ip);
 		IP6_EXTHDR_GET(th, struct tcphdr *, m, toff,
@@ -1299,10 +1315,8 @@ tcp_input(struct mbuf *m, ...)
 #endif
 #ifdef INET6
 	case 6:
-		ip = NULL;
 		iphlen = sizeof(struct ip6_hdr);
 		af = AF_INET6;
-		ip6 = mtod(m, struct ip6_hdr *);
 		IP6_EXTHDR_GET(th, struct tcphdr *, m, toff,
 			sizeof(struct tcphdr));
 		if (th == NULL) {
@@ -1349,23 +1363,6 @@ tcp_input(struct mbuf *m, ...)
 		m_freem(m);
 		return;
 	}
-	/*
-         * Enforce alignment requirements that are violated in
-	 * some cases, see kern/50766 for details.
-	 */
-	if (TCP_HDR_ALIGNED_P(th) == 0) {
-		m = m_copyup(m, toff + sizeof(struct tcphdr), 0);
-		if (m == NULL) {
-			TCP_STATINC(TCP_STAT_RCVSHORT);
-			return;
-		}
-		ip = mtod(m, struct ip *);
-#ifdef INET6
-		ip6 = mtod(m, struct ip6_hdr *);
-#endif
-		th = (struct tcphdr *)(mtod(m, char *) + toff);
-	}
-	KASSERT(TCP_HDR_ALIGNED_P(th));
 
 	/*
 	 * Check that TCP offset makes sense,
@@ -1601,7 +1598,6 @@ findpcb:
 			m_freem(in6p->in6p_options);
 			in6p->in6p_options = 0;
 		}
-		KASSERT(ip6 != NULL);
 		ip6_savecontrol(in6p, &in6p->in6p_options, ip6, m);
 	}
 #endif