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net: ipv4: Add ability to have GRE ignore DF bit in IPv4 payloads

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In the presence of firewalls which improperly block ICMP Unreachable
    (including Fragmentation Required) messages, Path MTU Discovery is
    prevented from working.

    A workaround is to handle IPv4 payloads opaquely, ignoring the DF bit--as
    is done for other payloads like AppleTalk--and doing transparent
    fragmentation and reassembly.

    Redux includes the enforcement of mutual exclusion between this feature
    and Path MTU Discovery as suggested by Alexander Duyck.

    Cc: Alexander Duyck <alexander.duyck@gmail.com>
    Reviewed-by: Stephen Hemminger <stephen@networkplumber.org>
    Signed-off-by: Philip Prindeville <philipp@redfish-solutions.com>

Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Philip Prindeville 2016-06-14 15:53:02 -06:00 committed by David S. Miller
parent 810e530bfa
commit 22a59be8b7
4 changed files with 36 additions and 10 deletions
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1
include/net/ip_tunnels.h
View File

@ -132,6 +132,7 @@ struct ip_tunnel {
int ip_tnl_net_id;
struct gro_cells gro_cells;
bool collect_md;
bool ignore_df;
};
#define TUNNEL_CSUM __cpu_to_be16(0x01)

1
include/uapi/linux/if_tunnel.h
View File

@ -113,6 +113,7 @@ enum {
IFLA_GRE_ENCAP_SPORT,
IFLA_GRE_ENCAP_DPORT,
IFLA_GRE_COLLECT_METADATA,
IFLA_GRE_IGNORE_DF,
__IFLA_GRE_MAX,
};

42
net/ipv4/ip_gre.c
View File

@ -841,17 +841,19 @@ out:
return ipgre_tunnel_validate(tb, data);
}
static void ipgre_netlink_parms(struct net_device *dev,
static int ipgre_netlink_parms(struct net_device *dev,
struct nlattr *data[],
struct nlattr *tb[],
struct ip_tunnel_parm *parms)
{
struct ip_tunnel *t = netdev_priv(dev);
memset(parms, 0, sizeof(*parms));
parms->iph.protocol = IPPROTO_GRE;
if (!data)
return;
return 0;
if (data[IFLA_GRE_LINK])
parms->link = nla_get_u32(data[IFLA_GRE_LINK]);
@ -880,16 +882,26 @@ static void ipgre_netlink_parms(struct net_device *dev,
if (data[IFLA_GRE_TOS])
parms->iph.tos = nla_get_u8(data[IFLA_GRE_TOS]);
if (!data[IFLA_GRE_PMTUDISC] || nla_get_u8(data[IFLA_GRE_PMTUDISC]))
if (!data[IFLA_GRE_PMTUDISC] || nla_get_u8(data[IFLA_GRE_PMTUDISC])) {
if (t->ignore_df)
return -EINVAL;
parms->iph.frag_off = htons(IP_DF);
}
if (data[IFLA_GRE_COLLECT_METADATA]) {
struct ip_tunnel *t = netdev_priv(dev);
t->collect_md = true;
if (dev->type == ARPHRD_IPGRE)
dev->type = ARPHRD_NONE;
}
if (data[IFLA_GRE_IGNORE_DF]) {
if (nla_get_u8(data[IFLA_GRE_IGNORE_DF])
&& (parms->iph.frag_off & htons(IP_DF)))
return -EINVAL;
t->ignore_df = !!nla_get_u8(data[IFLA_GRE_IGNORE_DF]);
}
return 0;
}
/* This function returns true when ENCAP attributes are present in the nl msg */
@ -960,16 +972,19 @@ static int ipgre_newlink(struct net *src_net, struct net_device *dev,
{
struct ip_tunnel_parm p;
struct ip_tunnel_encap ipencap;
int err;
if (ipgre_netlink_encap_parms(data, &ipencap)) {
struct ip_tunnel *t = netdev_priv(dev);
int err = ip_tunnel_encap_setup(t, &ipencap);
err = ip_tunnel_encap_setup(t, &ipencap);
if (err < 0)
return err;
}
ipgre_netlink_parms(dev, data, tb, &p);
err = ipgre_netlink_parms(dev, data, tb, &p);
if (err < 0)
return err;
return ip_tunnel_newlink(dev, tb, &p);
}
@ -978,16 +993,19 @@ static int ipgre_changelink(struct net_device *dev, struct nlattr *tb[],
{
struct ip_tunnel_parm p;
struct ip_tunnel_encap ipencap;
int err;
if (ipgre_netlink_encap_parms(data, &ipencap)) {
struct ip_tunnel *t = netdev_priv(dev);
int err = ip_tunnel_encap_setup(t, &ipencap);
err = ip_tunnel_encap_setup(t, &ipencap);
if (err < 0)
return err;
}
ipgre_netlink_parms(dev, data, tb, &p);
err = ipgre_netlink_parms(dev, data, tb, &p);
if (err < 0)
return err;
return ip_tunnel_changelink(dev, tb, &p);
}
@ -1024,6 +1042,8 @@ static size_t ipgre_get_size(const struct net_device *dev)
nla_total_size(2) +
/* IFLA_GRE_COLLECT_METADATA */
nla_total_size(0) +
/* IFLA_GRE_IGNORE_DF */
nla_total_size(1) +
0;
}
@ -1057,6 +1077,9 @@ static int ipgre_fill_info(struct sk_buff *skb, const struct net_device *dev)
t->encap.flags))
goto nla_put_failure;
if (nla_put_u8(skb, IFLA_GRE_IGNORE_DF, t->ignore_df))
goto nla_put_failure;
if (t->collect_md) {
if (nla_put_flag(skb, IFLA_GRE_COLLECT_METADATA))
goto nla_put_failure;
@ -1084,6 +1107,7 @@ static const struct nla_policy ipgre_policy[IFLA_GRE_MAX + 1] = {
[IFLA_GRE_ENCAP_SPORT] = { .type = NLA_U16 },
[IFLA_GRE_ENCAP_DPORT] = { .type = NLA_U16 },
[IFLA_GRE_COLLECT_METADATA] = { .type = NLA_FLAG },
[IFLA_GRE_IGNORE_DF] = { .type = NLA_U8 },
};
static struct rtnl_link_ops ipgre_link_ops __read_mostly = {

2
net/ipv4/ip_tunnel.c
View File

@ -682,7 +682,7 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev,
}
df = tnl_params->frag_off;
if (skb->protocol == htons(ETH_P_IP))
if (skb->protocol == htons(ETH_P_IP) && !tunnel->ignore_df)
df |= (inner_iph->frag_off&htons(IP_DF));
max_headroom = LL_RESERVED_SPACE(rt->dst.dev) + sizeof(struct iphdr)