netfilter: nft_fwd_netdev: allow to forward packets via neighbour layer

This allows us to forward packets from the netdev family via neighbour
layer, so you don't need an explicit link-layer destination when using
this expression from rules. The ttl/hop_limit field is decremented.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/include/uapi/linux/netfilter/nf_tables.h b/include/uapi/linux/netfilter/nf_tables.h
index 5c7eb9b..a089af0 100644 (file)
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -1260,10 +1260,14 @@ enum nft_dup_attributes {
  * enum nft_fwd_attributes - nf_tables fwd expression netlink attributes
  *
  * @NFTA_FWD_SREG_DEV: source register of output interface (NLA_U32: nft_register)
+ * @NFTA_FWD_SREG_ADDR: source register of destination address (NLA_U32: nft_register)
+ * @NFTA_FWD_NFPROTO: layer 3 family of source register address (NLA_U32: enum nfproto)
  */
 enum nft_fwd_attributes {
        NFTA_FWD_UNSPEC,
        NFTA_FWD_SREG_DEV,
+       NFTA_FWD_SREG_ADDR,
+       NFTA_FWD_NFPROTO,
        __NFTA_FWD_MAX
 };
 #define NFTA_FWD_MAX   (__NFTA_FWD_MAX - 1)

diff --git a/net/netfilter/nft_fwd_netdev.c b/net/netfilter/nft_fwd_netdev.c
index ce13a50..8abb989 100644 (file)
--- a/net/netfilter/nft_fwd_netdev.c
+++ b/net/netfilter/nft_fwd_netdev.c
@@ -12,8 +12,12 @@
 #include <linux/netlink.h>
 #include <linux/netfilter.h>
 #include <linux/netfilter/nf_tables.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
 #include <net/netfilter/nf_tables.h>
 #include <net/netfilter/nf_dup_netdev.h>
+#include <net/neighbour.h>
+#include <net/ip.h>
 
 struct nft_fwd_netdev {
        enum nft_registers      sreg_dev:8;
@@ -32,6 +36,8 @@ static void nft_fwd_netdev_eval(const struct nft_expr *expr,
 
 static const struct nla_policy nft_fwd_netdev_policy[NFTA_FWD_MAX + 1] = {
        [NFTA_FWD_SREG_DEV]     = { .type = NLA_U32 },
+       [NFTA_FWD_SREG_ADDR]    = { .type = NLA_U32 },
+       [NFTA_FWD_NFPROTO]      = { .type = NLA_U32 },
 };
 
 static int nft_fwd_netdev_init(const struct nft_ctx *ctx,
@@ -62,7 +68,133 @@ nla_put_failure:
        return -1;
 }
 
+struct nft_fwd_neigh {
+       enum nft_registers      sreg_dev:8;
+       enum nft_registers      sreg_addr:8;
+       u8                      nfproto;
+};
+
+static void nft_fwd_neigh_eval(const struct nft_expr *expr,
+                             struct nft_regs *regs,
+                             const struct nft_pktinfo *pkt)
+{
+       struct nft_fwd_neigh *priv = nft_expr_priv(expr);
+       void *addr = &regs->data[priv->sreg_addr];
+       int oif = regs->data[priv->sreg_dev];
+       unsigned int verdict = NF_STOLEN;
+       struct sk_buff *skb = pkt->skb;
+       struct net_device *dev;
+       int neigh_table;
+
+       switch (priv->nfproto) {
+       case NFPROTO_IPV4: {
+               struct iphdr *iph;
+
+               if (skb->protocol != htons(ETH_P_IP)) {
+                       verdict = NFT_BREAK;
+                       goto out;
+               }
+               if (skb_try_make_writable(skb, sizeof(*iph))) {
+                       verdict = NF_DROP;
+                       goto out;
+               }
+               iph = ip_hdr(skb);
+               ip_decrease_ttl(iph);
+               neigh_table = NEIGH_ARP_TABLE;
+               break;
+               }
+       case NFPROTO_IPV6: {
+               struct ipv6hdr *ip6h;
+
+               if (skb->protocol != htons(ETH_P_IPV6)) {
+                       verdict = NFT_BREAK;
+                       goto out;
+               }
+               if (skb_try_make_writable(skb, sizeof(*ip6h))) {
+                       verdict = NF_DROP;
+                       goto out;
+               }
+               ip6h = ipv6_hdr(skb);
+               ip6h->hop_limit--;
+               neigh_table = NEIGH_ND_TABLE;
+               break;
+               }
+       default:
+               verdict = NFT_BREAK;
+               goto out;
+       }
+
+       dev = dev_get_by_index_rcu(nft_net(pkt), oif);
+       if (dev == NULL)
+               return;
+
+       skb->dev = dev;
+       neigh_xmit(neigh_table, dev, addr, skb);
+out:
+       regs->verdict.code = verdict;
+}
+
+static int nft_fwd_neigh_init(const struct nft_ctx *ctx,
+                             const struct nft_expr *expr,
+                             const struct nlattr * const tb[])
+{
+       struct nft_fwd_neigh *priv = nft_expr_priv(expr);
+       unsigned int addr_len;
+       int err;
+
+       if (!tb[NFTA_FWD_SREG_DEV] ||
+           !tb[NFTA_FWD_SREG_ADDR] ||
+           !tb[NFTA_FWD_NFPROTO])
+               return -EINVAL;
+
+       priv->sreg_dev = nft_parse_register(tb[NFTA_FWD_SREG_DEV]);
+       priv->sreg_addr = nft_parse_register(tb[NFTA_FWD_SREG_ADDR]);
+       priv->nfproto = ntohl(nla_get_be32(tb[NFTA_FWD_NFPROTO]));
+
+       switch (priv->nfproto) {
+       case NFPROTO_IPV4:
+               addr_len = sizeof(struct in_addr);
+               break;
+       case NFPROTO_IPV6:
+               addr_len = sizeof(struct in6_addr);
+               break;
+       default:
+               return -EOPNOTSUPP;
+       }
+
+       err = nft_validate_register_load(priv->sreg_dev, sizeof(int));
+       if (err < 0)
+               return err;
+
+       return nft_validate_register_load(priv->sreg_addr, addr_len);
+}
+
+static const struct nft_expr_ops nft_fwd_netdev_ingress_ops;
+
+static int nft_fwd_neigh_dump(struct sk_buff *skb, const struct nft_expr *expr)
+{
+       struct nft_fwd_neigh *priv = nft_expr_priv(expr);
+
+       if (nft_dump_register(skb, NFTA_FWD_SREG_DEV, priv->sreg_dev) ||
+           nft_dump_register(skb, NFTA_FWD_SREG_ADDR, priv->sreg_addr) ||
+           nla_put_be32(skb, NFTA_FWD_NFPROTO, htonl(priv->nfproto)))
+               goto nla_put_failure;
+
+       return 0;
+
+nla_put_failure:
+       return -1;
+}
+
 static struct nft_expr_type nft_fwd_netdev_type;
+static const struct nft_expr_ops nft_fwd_neigh_netdev_ops = {
+       .type           = &nft_fwd_netdev_type,
+       .size           = NFT_EXPR_SIZE(sizeof(struct nft_fwd_neigh)),
+       .eval           = nft_fwd_neigh_eval,
+       .init           = nft_fwd_neigh_init,
+       .dump           = nft_fwd_neigh_dump,
+};
+
 static const struct nft_expr_ops nft_fwd_netdev_ops = {
        .type           = &nft_fwd_netdev_type,
        .size           = NFT_EXPR_SIZE(sizeof(struct nft_fwd_netdev)),
@@ -71,10 +203,22 @@ static const struct nft_expr_ops nft_fwd_netdev_ops = {
        .dump           = nft_fwd_netdev_dump,
 };
 
+static const struct nft_expr_ops *
+nft_fwd_select_ops(const struct nft_ctx *ctx,
+                  const struct nlattr * const tb[])
+{
+       if (tb[NFTA_FWD_SREG_ADDR])
+               return &nft_fwd_neigh_netdev_ops;
+       if (tb[NFTA_FWD_SREG_DEV])
+               return &nft_fwd_netdev_ops;
+
+        return ERR_PTR(-EOPNOTSUPP);
+}
+
 static struct nft_expr_type nft_fwd_netdev_type __read_mostly = {
        .family         = NFPROTO_NETDEV,
        .name           = "fwd",
-       .ops            = &nft_fwd_netdev_ops,
+       .select_ops     = nft_fwd_select_ops,
        .policy         = nft_fwd_netdev_policy,
        .maxattr        = NFTA_FWD_MAX,
        .owner          = THIS_MODULE,