datapath: Allow attaching helpers to ct action

Add support for using conntrack helpers to assist protocol detection.
The new OVS_CT_ATTR_HELPER attribute of the CT action specifies a helper
to be used for this connection. If no helper is specified, then helpers
will be automatically applied as per the sysctl configuration of
net.netfilter.nf_conntrack_helper.

The helper may be specified as part of the conntrack action, eg:
ct(helper=ftp). Initial packets for related connections should be
committed to allow later packets for the flow to be considered
established.

Example ovs-ofctl flows allowing FTP connections from ports 1->2:
in_port=1,tcp,action=ct(helper=ftp,commit),2
in_port=2,tcp,ct_state=-trk,action=ct(recirc)
in_port=2,tcp,ct_state=+trk-new+est,action=1
in_port=2,tcp,ct_state=+trk+rel,action=1

Upstream: cae3a26 "openvswitch: Allow attaching helpers to ct action"
Signed-off-by: Joe Stringer <joestringer@nicira.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>

diff --git a/datapath/conntrack.c b/datapath/conntrack.c
index 9ea3ed3..9d3ee47 100644 (file)
--- a/datapath/conntrack.c
+++ b/datapath/conntrack.c
@@ -21,6 +21,7 @@
 #include <linux/openvswitch.h>
 #include <net/ip.h>
 #include <net/netfilter/nf_conntrack_core.h>
+#include <net/netfilter/nf_conntrack_helper.h>
 #include <net/netfilter/nf_conntrack_labels.h>
 #include <net/netfilter/nf_conntrack_zones.h>
 #include <net/netfilter/ipv6/nf_defrag_ipv6.h>
@@ -49,6 +50,7 @@ struct md_label {
 
 /* Conntrack action context for execution. */
 struct ovs_conntrack_info {
+       struct nf_conntrack_helper *helper;
        struct nf_conntrack_zone zone;
        struct nf_conn *ct;
        u32 flags;
@@ -57,6 +59,8 @@ struct ovs_conntrack_info {
        struct md_label label;
 };
 
+static void __ovs_ct_free_action(struct ovs_conntrack_info *ct_info);
+
 static u16 key_to_nfproto(const struct sw_flow_key *key)
 {
        switch (ntohs(key->eth.type)) {
@@ -240,6 +244,51 @@ static int ovs_ct_set_label(struct sk_buff *skb, struct sw_flow_key *key,
        return 0;
 }
 
+/* 'skb' should already be pulled to nh_ofs. */
+static int ovs_ct_helper(struct sk_buff *skb, u16 proto)
+{
+       const struct nf_conntrack_helper *helper;
+       const struct nf_conn_help *help;
+       enum ip_conntrack_info ctinfo;
+       unsigned int protoff;
+       struct nf_conn *ct;
+
+       ct = nf_ct_get(skb, &ctinfo);
+       if (!ct || ctinfo == IP_CT_RELATED_REPLY)
+               return NF_ACCEPT;
+
+       help = nfct_help(ct);
+       if (!help)
+               return NF_ACCEPT;
+
+       helper = rcu_dereference(help->helper);
+       if (!helper)
+               return NF_ACCEPT;
+
+       switch (proto) {
+       case NFPROTO_IPV4:
+               protoff = ip_hdrlen(skb);
+               break;
+       case NFPROTO_IPV6: {
+               u8 nexthdr = ipv6_hdr(skb)->nexthdr;
+               __be16 frag_off;
+
+               protoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr),
+                                          &nexthdr, &frag_off);
+               if (protoff < 0 || (frag_off & htons(~0x7)) != 0) {
+                       pr_debug("proto header not found\n");
+                       return NF_ACCEPT;
+               }
+               break;
+       }
+       default:
+               WARN_ONCE(1, "helper invoked on non-IP family!");
+               return NF_DROP;
+       }
+
+       return helper->help(skb, protoff, ct, ctinfo);
+}
+
 static int handle_fragments(struct net *net, struct sw_flow_key *key,
                            u16 zone, struct sk_buff *skb)
 {
@@ -317,6 +366,13 @@ static bool skb_nfct_cached(const struct net *net, const struct sk_buff *skb,
                return false;
        if (!nf_ct_zone_equal_any(info->ct, nf_ct_zone(ct)))
                return false;
+       if (info->helper) {
+               struct nf_conn_help *help;
+
+               help = nf_ct_ext_find(ct, NF_CT_EXT_HELPER);
+               if (help && rcu_access_pointer(help->helper) != info->helper)
+                       return false;
+       }
 
        return true;
 }
@@ -345,6 +401,11 @@ static int __ovs_ct_lookup(struct net *net, const struct sw_flow_key *key,
                if (nf_conntrack_in(net, info->family, NF_INET_FORWARD,
                                    skb) != NF_ACCEPT)
                        return -ENOENT;
+
+               if (ovs_ct_helper(skb, info->family) != NF_ACCEPT) {
+                       WARN_ONCE(1, "helper rejected packet");
+                       return -EINVAL;
+               }
        }
 
        return 0;
@@ -453,6 +514,30 @@ err:
        return err;
 }
 
+static int ovs_ct_add_helper(struct ovs_conntrack_info *info, const char *name,
+                            const struct sw_flow_key *key, bool log)
+{
+       struct nf_conntrack_helper *helper;
+       struct nf_conn_help *help;
+
+       helper = nf_conntrack_helper_try_module_get(name, info->family,
+                                                   key->ip.proto);
+       if (!helper) {
+               OVS_NLERR(log, "Unknown helper \"%s\"", name);
+               return -EINVAL;
+       }
+
+       help = nf_ct_helper_ext_add(info->ct, helper, GFP_KERNEL);
+       if (!help) {
+               module_put(helper->me);
+               return -ENOMEM;
+       }
+
+       rcu_assign_pointer(help->helper, helper);
+       info->helper = helper;
+       return 0;
+}
+
 static const struct ovs_ct_len_tbl ovs_ct_attr_lens[OVS_CT_ATTR_MAX + 1] = {
        [OVS_CT_ATTR_FLAGS]     = { .minlen = sizeof(u32),
                                    .maxlen = sizeof(u32) },
@@ -462,10 +547,12 @@ static const struct ovs_ct_len_tbl ovs_ct_attr_lens[OVS_CT_ATTR_MAX + 1] = {
                                    .maxlen = sizeof(struct md_mark) },
        [OVS_CT_ATTR_LABEL]     = { .minlen = sizeof(struct md_label),
                                    .maxlen = sizeof(struct md_label) },
+       [OVS_CT_ATTR_HELPER]    = { .minlen = 1,
+                                   .maxlen = NF_CT_HELPER_NAME_LEN }
 };
 
 static int parse_ct(const struct nlattr *attr, struct ovs_conntrack_info *info,
-                   bool log)
+                   const char **helper, bool log)
 {
        struct nlattr *a;
        int rem;
@@ -513,6 +600,13 @@ static int parse_ct(const struct nlattr *attr, struct ovs_conntrack_info *info,
                        break;
                }
 #endif
+               case OVS_CT_ATTR_HELPER:
+                       *helper = nla_data(a);
+                       if (!memchr(*helper, '\0', nla_len(a))) {
+                               OVS_NLERR(log, "Invalid conntrack helper");
+                               return -EINVAL;
+                       }
+                       break;
                default:
                        OVS_NLERR(log, "Unknown conntrack attr (%d)",
                                  type);
@@ -553,6 +647,7 @@ int ovs_ct_copy_action(struct net *net, const struct nlattr *attr,
                       struct sw_flow_actions **sfa,  bool log)
 {
        struct ovs_conntrack_info ct_info;
+       const char *helper = NULL;
        u16 family;
        int err;
 
@@ -568,7 +663,7 @@ int ovs_ct_copy_action(struct net *net, const struct nlattr *attr,
        nf_ct_zone_init(&ct_info.zone, NF_CT_DEFAULT_ZONE_ID,
                        NF_CT_DEFAULT_ZONE_DIR, 0);
 
-       err = parse_ct(attr, &ct_info, log);
+       err = parse_ct(attr, &ct_info, &helper, log);
        if (err)
                return err;
 
@@ -578,6 +673,11 @@ int ovs_ct_copy_action(struct net *net, const struct nlattr *attr,
                OVS_NLERR(log, "Failed to allocate conntrack template");
                return -ENOMEM;
        }
+       if (helper) {
+               err = ovs_ct_add_helper(&ct_info, helper, key, log);
+               if (err)
+                       goto err_free_ct;
+       }
 
        err = ovs_nla_add_action(sfa, OVS_ACTION_ATTR_CT, &ct_info,
                                 sizeof(ct_info), log);
@@ -588,7 +688,7 @@ int ovs_ct_copy_action(struct net *net, const struct nlattr *attr,
        nf_conntrack_get(&ct_info.ct->ct_general);
        return 0;
 err_free_ct:
-       nf_conntrack_free(ct_info.ct);
+       __ovs_ct_free_action(&ct_info);
        return err;
 }
 
@@ -614,6 +714,11 @@ int ovs_ct_action_to_attr(const struct ovs_conntrack_info *ct_info,
            nla_put(skb, OVS_CT_ATTR_LABEL, sizeof(ct_info->label),
                    &ct_info->label))
                return -EMSGSIZE;
+       if (ct_info->helper) {
+               if (nla_put_string(skb, OVS_CT_ATTR_HELPER,
+                                  ct_info->helper->name))
+                       return -EMSGSIZE;
+       }
 
        nla_nest_end(skb, start);
 
@@ -624,6 +729,13 @@ void ovs_ct_free_action(const struct nlattr *a)
 {
        struct ovs_conntrack_info *ct_info = nla_data(a);
 
+       __ovs_ct_free_action(ct_info);
+}
+
+static void __ovs_ct_free_action(struct ovs_conntrack_info *ct_info)
+{
+       if (ct_info->helper)
+               module_put(ct_info->helper->me);
        if (ct_info->ct)
                nf_ct_tmpl_free(ct_info->ct);
 }