ip6_gre: Fix MTU setting

In ip6gre_tnl_link_config set t->tun_len and t->hlen correctly for the
configuration. For hard_header_len and mtu calculation include
IPv6 header and encapsulation overhead.

In ip6gre_tunnel_init_common set t->tun_len and t->hlen correctly for
the configuration. Revert to setting hard_header_len instead of
needed_headroom.

Tested:

./ip link add name tun8 type ip6gretap remote \
2401:db00:20:911a:face:0:27:0 local \
2401:db00:20:911a:face:0:25:0 ttl 225

Gives MTU of 1434. That is equal to 1500 - 40 - 14 - 4 - 8.

./ip link add name tun8 type ip6gretap remote \
2401:db00:20:911a:face:0:27:0 local \
2401:db00:20:911a:face:0:25:0 ttl 225 okey 123

Gives MTU of 1430. That is equal to 1500 - 40 - 14 - 4 - 8 - 4.

Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 47b671a..6d0aa94 100644 (file)
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -700,7 +700,7 @@ static void ip6gre_tnl_link_config(struct ip6_tnl *t, int set_mtu)
        struct net_device *dev = t->dev;
        struct __ip6_tnl_parm *p = &t->parms;
        struct flowi6 *fl6 = &t->fl.u.ip6;
-       int addend = sizeof(struct ipv6hdr) + 4;
+       int t_hlen;
 
        if (dev->type != ARPHRD_ETHER) {
                memcpy(dev->dev_addr, &p->laddr, sizeof(struct in6_addr));
@@ -727,16 +727,11 @@ static void ip6gre_tnl_link_config(struct ip6_tnl *t, int set_mtu)
        else
                dev->flags &= ~IFF_POINTOPOINT;
 
-       /* Precalculate GRE options length */
-       if (t->parms.o_flags&(GRE_CSUM|GRE_KEY|GRE_SEQ)) {
-               if (t->parms.o_flags&GRE_CSUM)
-                       addend += 4;
-               if (t->parms.o_flags&GRE_KEY)
-                       addend += 4;
-               if (t->parms.o_flags&GRE_SEQ)
-                       addend += 4;
-       }
-       t->hlen = addend;
+       t->tun_hlen = gre_calc_hlen(t->parms.o_flags);
+
+       t->hlen = t->tun_hlen;
+
+       t_hlen = t->hlen + sizeof(struct ipv6hdr);
 
        if (p->flags & IP6_TNL_F_CAP_XMIT) {
                int strict = (ipv6_addr_type(&p->raddr) &
@@ -750,10 +745,11 @@ static void ip6gre_tnl_link_config(struct ip6_tnl *t, int set_mtu)
                        return;
 
                if (rt->dst.dev) {
-                       dev->hard_header_len = rt->dst.dev->hard_header_len + addend;
+                       dev->hard_header_len = rt->dst.dev->hard_header_len +
+                                              t_hlen;
 
                        if (set_mtu) {
-                               dev->mtu = rt->dst.dev->mtu - addend;
+                               dev->mtu = rt->dst.dev->mtu - t_hlen;
                                if (!(t->parms.flags & IP6_TNL_F_IGN_ENCAP_LIMIT))
                                        dev->mtu -= 8;
                                if (dev->type == ARPHRD_ETHER)
@@ -1027,11 +1023,12 @@ static int ip6gre_tunnel_init_common(struct net_device *dev)
 
        tunnel->tun_hlen = gre_calc_hlen(tunnel->parms.o_flags);
 
-       t_hlen = tunnel->hlen + sizeof(struct ipv6hdr);
+       tunnel->hlen = tunnel->tun_hlen;
 
-       dev->needed_headroom    = LL_MAX_HEADER + t_hlen + 4;
-       dev->mtu                = ETH_DATA_LEN - t_hlen - 4;
+       t_hlen = tunnel->hlen + sizeof(struct ipv6hdr);
 
+       dev->hard_header_len = LL_MAX_HEADER + t_hlen;
+       dev->mtu = ETH_DATA_LEN - t_hlen;
        if (!(tunnel->parms.flags & IP6_TNL_F_IGN_ENCAP_LIMIT))
                dev->mtu -= 8;