4 files changed, 21 insertions, 4 deletions

diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
index 46c9e2ccdf02..7d83f90f203f 100644
--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h
@@ -45,6 +45,7 @@ struct inet_connection_sock_af_ops {
                                       struct dst_entry *dst);
         struct inet_peer *(*get_peer)(struct sock *sk, bool *release_it);
         u16         net_header_len;
+        u16         net_frag_header_len;
         u16         sockaddr_len;
         int         (*setsockopt)(struct sock *sk, int level, int optname, 
                                   char __user *optval, unsigned int optlen);
diff --git a/include/net/tcp.h b/include/net/tcp.h
index fc880e92164a..0fb84de6da36 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -544,8 +544,8 @@ extern int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
 
 extern void tcp_initialize_rcv_mss(struct sock *sk);
 
-extern int tcp_mtu_to_mss(const struct sock *sk, int pmtu);
-extern int tcp_mss_to_mtu(const struct sock *sk, int mss);
+extern int tcp_mtu_to_mss(struct sock *sk, int pmtu);
+extern int tcp_mss_to_mtu(struct sock *sk, int mss);
 extern void tcp_mtup_init(struct sock *sk);
 extern void tcp_valid_rtt_meas(struct sock *sk, u32 seq_rtt);
 
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 7b7cf3811348..834e89fc541b 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1150,7 +1150,7 @@ int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
 }
 
 /* Calculate MSS. Not accounting for SACKs here.  */
-int tcp_mtu_to_mss(const struct sock *sk, int pmtu)
+int tcp_mtu_to_mss(struct sock *sk, int pmtu)
 {
         const struct tcp_sock *tp = tcp_sk(sk);
         const struct inet_connection_sock *icsk = inet_csk(sk);
@@ -1161,6 +1161,14 @@ int tcp_mtu_to_mss(const struct sock *sk, int pmtu)
          */
         mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
 
+        /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
+        if (icsk->icsk_af_ops->net_frag_header_len) {
+                const struct dst_entry *dst = __sk_dst_get(sk);
+
+                if (dst && dst_allfrag(dst))
+                        mss_now -= icsk->icsk_af_ops->net_frag_header_len;
+        }
+
         /* Clamp it (mss_clamp does not include tcp options) */
         if (mss_now > tp->rx_opt.mss_clamp)
                 mss_now = tp->rx_opt.mss_clamp;
@@ -1179,7 +1187,7 @@ int tcp_mtu_to_mss(const struct sock *sk, int pmtu)
 }
 
 /* Inverse of above */
-int tcp_mss_to_mtu(const struct sock *sk, int mss)
+int tcp_mss_to_mtu(struct sock *sk, int mss)
 {
         const struct tcp_sock *tp = tcp_sk(sk);
         const struct inet_connection_sock *icsk = inet_csk(sk);
@@ -1190,6 +1198,13 @@ int tcp_mss_to_mtu(const struct sock *sk, int mss)
               icsk->icsk_ext_hdr_len +
               icsk->icsk_af_ops->net_header_len;
 
+        /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
+        if (icsk->icsk_af_ops->net_frag_header_len) {
+                const struct dst_entry *dst = __sk_dst_get(sk);
+
+                if (dst && dst_allfrag(dst))
+                        mtu += icsk->icsk_af_ops->net_frag_header_len;
+        }
         return mtu;
 }
 
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index cdbf292ad208..57b210969834 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1778,6 +1778,7 @@ static const struct inet_connection_sock_af_ops ipv6_specific = {
         .syn_recv_sock     = tcp_v6_syn_recv_sock,
         .get_peer          = tcp_v6_get_peer,
         .net_header_len    = sizeof(struct ipv6hdr),
+        .net_frag_header_len = sizeof(struct frag_hdr),
         .setsockopt        = ipv6_setsockopt,
         .getsockopt        = ipv6_getsockopt,
         .addr2sockaddr     = inet6_csk_addr2sockaddr,