vxlan: Allow configuration of DF behaviour

Allow users to set the IPv4 DF bit in outgoing packets, or to inherit its
value from the IPv4 inner header. If the encapsulated protocol is IPv6 and
DF is configured to be inherited, always set it.

For IPv4, inheriting DF from the inner header was probably intended from
the very beginning judging by the comment to vxlan_xmit(), but it wasn't
actually implemented -- also because it would have done more harm than
good, without handling for ICMP Fragmentation Needed messages.

According to RFC 7348, "Path MTU discovery MAY be used". An expired RFC
draft, draft-saum-nvo3-pmtud-over-vxlan-05, whose purpose was to describe
PMTUD implementation, says that "is a MUST that Vxlan gateways [...]
SHOULD set the DF-bit [...]", whatever that means.

Given this background, the only sane option is probably to let the user
decide, and keep the current behaviour as default.

This only applies to non-lwt tunnels: if an external control plane is
used, tunnel key will still control the DF flag.

v2:
- DF behaviour configuration only applies for non-lwt tunnels, move DF
  setting to if (!info) block in vxlan_xmit_one() (Stephen Hemminger)

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index 0851af6733f3697d9c41ab61092512a6eda1098a..c3e65e78f015636bb3a4f71062bd792c9164785d 100644 (file)
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -2278,13 +2278,24 @@ static void vxlan_xmit_one(struct sk_buff *skb, struct net_device *dev,
                        goto tx_error;
                }
 
-               /* Bypass encapsulation if the destination is local */
                if (!info) {
+                       /* Bypass encapsulation if the destination is local */
                        err = encap_bypass_if_local(skb, dev, vxlan, dst,
                                                    dst_port, ifindex, vni,
                                                    &rt->dst, rt->rt_flags);
                        if (err)
                                goto out_unlock;
+
+                       if (vxlan->cfg.df == VXLAN_DF_SET) {
+                               df = htons(IP_DF);
+                       } else if (vxlan->cfg.df == VXLAN_DF_INHERIT) {
+                               struct ethhdr *eth = eth_hdr(skb);
+
+                               if (ntohs(eth->h_proto) == ETH_P_IPV6 ||
+                                   (ntohs(eth->h_proto) == ETH_P_IP &&
+                                    old_iph->frag_off & htons(IP_DF)))
+                                       df = htons(IP_DF);
+                       }
                } else if (info->key.tun_flags & TUNNEL_DONT_FRAGMENT) {
                        df = htons(IP_DF);
                }
@@ -2837,6 +2848,7 @@ static const struct nla_policy vxlan_policy[IFLA_VXLAN_MAX + 1] = {
        [IFLA_VXLAN_GPE]        = { .type = NLA_FLAG, },
        [IFLA_VXLAN_REMCSUM_NOPARTIAL]  = { .type = NLA_FLAG },
        [IFLA_VXLAN_TTL_INHERIT]        = { .type = NLA_FLAG },
+       [IFLA_VXLAN_DF]         = { .type = NLA_U8 },
 };
 
 static int vxlan_validate(struct nlattr *tb[], struct nlattr *data[],
@@ -2893,6 +2905,16 @@ static int vxlan_validate(struct nlattr *tb[], struct nlattr *data[],
                }
        }
 
+       if (data[IFLA_VXLAN_DF]) {
+               enum ifla_vxlan_df df = nla_get_u8(data[IFLA_VXLAN_DF]);
+
+               if (df < 0 || df > VXLAN_DF_MAX) {
+                       NL_SET_ERR_MSG_ATTR(extack, tb[IFLA_VXLAN_DF],
+                                           "Invalid DF attribute");
+                       return -EINVAL;
+               }
+       }
+
        return 0;
 }
 
@@ -3538,6 +3560,9 @@ static int vxlan_nl2conf(struct nlattr *tb[], struct nlattr *data[],
                conf->mtu = nla_get_u32(tb[IFLA_MTU]);
        }
 
+       if (data[IFLA_VXLAN_DF])
+               conf->df = nla_get_u8(data[IFLA_VXLAN_DF]);
+
        return 0;
 }
 
@@ -3630,6 +3655,7 @@ static size_t vxlan_get_size(const struct net_device *dev)
                nla_total_size(sizeof(__u8)) +  /* IFLA_VXLAN_TTL */
                nla_total_size(sizeof(__u8)) +  /* IFLA_VXLAN_TTL_INHERIT */
                nla_total_size(sizeof(__u8)) +  /* IFLA_VXLAN_TOS */
+               nla_total_size(sizeof(__u8)) +  /* IFLA_VXLAN_DF */
                nla_total_size(sizeof(__be32)) + /* IFLA_VXLAN_LABEL */
                nla_total_size(sizeof(__u8)) +  /* IFLA_VXLAN_LEARNING */
                nla_total_size(sizeof(__u8)) +  /* IFLA_VXLAN_PROXY */
@@ -3696,6 +3722,7 @@ static int vxlan_fill_info(struct sk_buff *skb, const struct net_device *dev)
            nla_put_u8(skb, IFLA_VXLAN_TTL_INHERIT,
                       !!(vxlan->cfg.flags & VXLAN_F_TTL_INHERIT)) ||
            nla_put_u8(skb, IFLA_VXLAN_TOS, vxlan->cfg.tos) ||
+           nla_put_u8(skb, IFLA_VXLAN_DF, vxlan->cfg.df) ||
            nla_put_be32(skb, IFLA_VXLAN_LABEL, vxlan->cfg.label) ||
            nla_put_u8(skb, IFLA_VXLAN_LEARNING,
                        !!(vxlan->cfg.flags & VXLAN_F_LEARN)) ||

diff --git a/include/net/vxlan.h b/include/net/vxlan.h
index 03431c148e1677bd3cb140996e8d8a14af9d8a42..ec999c49df1f3e285dc45713c592838257e5123b 100644 (file)
--- a/include/net/vxlan.h
+++ b/include/net/vxlan.h
@@ -216,6 +216,7 @@ struct vxlan_config {
        unsigned long           age_interval;
        unsigned int            addrmax;
        bool                    no_share;
+       enum ifla_vxlan_df      df;
 };
 
 struct vxlan_dev_node {

diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index 1debfa42cba1a965fcca8532d8b63c0bf4cf7949..efc588949431e288e1e03f8827a686ebefbd13b7 100644 (file)
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -533,6 +533,7 @@ enum {
        IFLA_VXLAN_LABEL,
        IFLA_VXLAN_GPE,
        IFLA_VXLAN_TTL_INHERIT,
+       IFLA_VXLAN_DF,
        __IFLA_VXLAN_MAX
 };
 #define IFLA_VXLAN_MAX (__IFLA_VXLAN_MAX - 1)
@@ -542,6 +543,14 @@ struct ifla_vxlan_port_range {
        __be16  high;
 };
 
+enum ifla_vxlan_df {
+       VXLAN_DF_UNSET = 0,
+       VXLAN_DF_SET,
+       VXLAN_DF_INHERIT,
+       __VXLAN_DF_END,
+       VXLAN_DF_MAX = __VXLAN_DF_END - 1,
+};
+
 /* GENEVE section */
 enum {
        IFLA_GENEVE_UNSPEC,