2 files changed, 26 insertions, 4 deletions

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index feae495a0a30..aedaa2cd4237 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -496,6 +496,7 @@ out:
 static inline int l2tp_verify_udp_checksum(struct sock *sk,
                                            struct sk_buff *skb)
 {
+        struct l2tp_tunnel *tunnel = (struct l2tp_tunnel *)sk->sk_user_data;
         struct udphdr *uh = udp_hdr(skb);
         u16 ulen = ntohs(uh->len);
         __wsum psum;
@@ -504,7 +505,7 @@ static inline int l2tp_verify_udp_checksum(struct sock *sk,
                 return 0;
 
 #if IS_ENABLED(CONFIG_IPV6)
-        if (sk->sk_family == PF_INET6) {
+        if (sk->sk_family == PF_INET6 && !tunnel->v4mapped) {
                 if (!uh->check) {
                         LIMIT_NETDEBUG(KERN_INFO "L2TP: IPv6: checksum is 0\n");
                         return 1;
@@ -1128,7 +1129,7 @@ static int l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb,
         /* Queue the packet to IP for output */
         skb->local_df = 1;
 #if IS_ENABLED(CONFIG_IPV6)
-        if (skb->sk->sk_family == PF_INET6)
+        if (skb->sk->sk_family == PF_INET6 && !tunnel->v4mapped)
                 error = inet6_csk_xmit(skb, NULL);
         else
 #endif
@@ -1255,7 +1256,7 @@ int l2tp_xmit_skb(struct l2tp_session *session, struct sk_buff *skb, int hdr_len
 
                 /* Calculate UDP checksum if configured to do so */
 #if IS_ENABLED(CONFIG_IPV6)
-                if (sk->sk_family == PF_INET6)
+                if (sk->sk_family == PF_INET6 && !tunnel->v4mapped)
                         l2tp_xmit_ipv6_csum(sk, skb, udp_len);
                 else
 #endif
@@ -1704,6 +1705,24 @@ int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id, u32
         if (cfg != NULL)
                 tunnel->debug = cfg->debug;
 
+#if IS_ENABLED(CONFIG_IPV6)
+        if (sk->sk_family == PF_INET6) {
+                struct ipv6_pinfo *np = inet6_sk(sk);
+
+                if (ipv6_addr_v4mapped(&np->saddr) &&
+                    ipv6_addr_v4mapped(&np->daddr)) {
+                        struct inet_sock *inet = inet_sk(sk);
+
+                        tunnel->v4mapped = true;
+                        inet->inet_saddr = np->saddr.s6_addr32[3];
+                        inet->inet_rcv_saddr = np->rcv_saddr.s6_addr32[3];
+                        inet->inet_daddr = np->daddr.s6_addr32[3];
+                } else {
+                        tunnel->v4mapped = false;
+                }
+        }
+#endif
+
         /* Mark socket as an encapsulation socket. See net/ipv4/udp.c */
         tunnel->encap = encap;
         if (encap == L2TP_ENCAPTYPE_UDP) {
@@ -1712,7 +1731,7 @@ int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id, u32
                 udp_sk(sk)->encap_rcv = l2tp_udp_encap_recv;
                 udp_sk(sk)->encap_destroy = l2tp_udp_encap_destroy;
 #if IS_ENABLED(CONFIG_IPV6)
-                if (sk->sk_family == PF_INET6)
+                if (sk->sk_family == PF_INET6 && !tunnel->v4mapped)
                         udpv6_encap_enable();
                 else
 #endif
diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index 66a559b104b6..6f251cbc2ed7 100644
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -194,6 +194,9 @@ struct l2tp_tunnel {
         struct sock             *sock;          /* Parent socket */
         int                     fd;             /* Parent fd, if tunnel socket
                                                  * was created by userspace */
+#if IS_ENABLED(CONFIG_IPV6)
+        bool                    v4mapped;
+#endif
 
         struct work_struct      del_work;