Add SYNPROXY module support in nf_tables. It preserves the behaviour of the
SYNPROXY target of iptables but structured in a different way to propose
improvements in the future.
Signed-off-by: Fernando Fernandez Mancera <ffmancera@xxxxxxxxxx>
---
v1: initial patch
v2: add IPV6 module checks
v3: move common eval parts into a function, reorder init function, remove the unnecessary headers and adapt the header to the rename patch
---
include/net/netfilter/nf_conntrack_synproxy.h | 1 +
include/uapi/linux/netfilter/nf_SYNPROXY.h | 4 +
include/uapi/linux/netfilter/nf_tables.h | 17 +
net/netfilter/Kconfig | 11 +
net/netfilter/Makefile | 1 +
net/netfilter/nft_synproxy.c | 298 ++++++++++++++++++
6 files changed, 332 insertions(+)
create mode 100644 net/netfilter/nft_synproxy.c
diff --git a/include/net/netfilter/nf_conntrack_synproxy.h b/include/net/netfilter/nf_conntrack_synproxy.h
index c5659dcf5b1a..8f00125b06f4 100644
--- a/include/net/netfilter/nf_conntrack_synproxy.h
+++ b/include/net/netfilter/nf_conntrack_synproxy.h
@@ -2,6 +2,7 @@
#ifndef _NF_CONNTRACK_SYNPROXY_H
#define _NF_CONNTRACK_SYNPROXY_H
+#include <net/netfilter/nf_conntrack_seqadj.h>
#include <net/netns/generic.h>
struct nf_conn_synproxy {
diff --git a/include/uapi/linux/netfilter/nf_SYNPROXY.h b/include/uapi/linux/netfilter/nf_SYNPROXY.h
index 068d1b3a6f06..6f3791c8946f 100644
--- a/include/uapi/linux/netfilter/nf_SYNPROXY.h
+++ b/include/uapi/linux/netfilter/nf_SYNPROXY.h
@@ -9,6 +9,10 @@
#define NF_SYNPROXY_OPT_SACK_PERM 0x04
#define NF_SYNPROXY_OPT_TIMESTAMP 0x08
#define NF_SYNPROXY_OPT_ECN 0x10
+#define NF_SYNPROXY_OPT_MASK (NF_SYNPROXY_OPT_MSS | \
+ NF_SYNPROXY_OPT_WSCALE | \
+ NF_SYNPROXY_OPT_SACK_PERM | \
+ NF_SYNPROXY_OPT_TIMESTAMP)
struct nf_synproxy_info {
__u8 options;
diff --git a/include/uapi/linux/netfilter/nf_tables.h b/include/uapi/linux/netfilter/nf_tables.h
index c6c8ec5c7c00..302c25af17d7 100644
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -1551,6 +1551,23 @@ enum nft_osf_flags {
NFT_OSF_F_VERSION = (1 << 0),
};
+/**
+ * enum nft_synproxy_attributes - nf_tables synproxy expression
+ * netlink attributes
+ *
+ * @NFTA_SYNPROXY_MSS: mss value sent to the backend (NLA_U16)
+ * @NFTA_SYNPROXY_WSCALE: wscale value sent to the backend (NLA_U8)
+ * @NFTA_SYNPROXY_FLAGS: flags (NLA_U32)
+ */
+enum nft_synproxy_attributes {
+ NFTA_SYNPROXY_UNSPEC,
+ NFTA_SYNPROXY_MSS,
+ NFTA_SYNPROXY_WSCALE,
+ NFTA_SYNPROXY_FLAGS,
+ __NFTA_SYNPROXY_MAX,
+};
+#define NFTA_SYNPROXY_MAX (__NFTA_SYNPROXY_MAX - 1)
+
/**
* enum nft_device_attributes - nf_tables device netlink attributes
*
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index 21025c2c605b..d59742408d9b 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -651,6 +651,17 @@ config NFT_TPROXY
help
This makes transparent proxy support available in nftables.
+config NFT_SYNPROXY
+ tristate "Netfilter nf_tables SYNPROXY expression support"
+ depends on NF_CONNTRACK && NETFILTER_ADVANCED
+ select NETFILTER_SYNPROXY
+ select SYN_COOKIES
+ help
+ The SYNPROXY expression allows you to intercept TCP connections and
+ establish them using syncookies before they are passed on to the
+ server. This allows to avoid conntrack and server resource usage
+ during SYN-flood attacks.
+
if NF_TABLES_NETDEV
config NF_DUP_NETDEV
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index 72cca6b48960..deada20975ff 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -110,6 +110,7 @@ obj-$(CONFIG_NFT_SOCKET) += nft_socket.o
obj-$(CONFIG_NFT_OSF) += nft_osf.o
obj-$(CONFIG_NFT_TPROXY) += nft_tproxy.o
obj-$(CONFIG_NFT_XFRM) += nft_xfrm.o
+obj-$(CONFIG_NFT_SYNPROXY) += nft_synproxy.o
obj-$(CONFIG_NFT_NAT) += nft_chain_nat.o
diff --git a/net/netfilter/nft_synproxy.c b/net/netfilter/nft_synproxy.c
new file mode 100644
index 000000000000..33c1318a7c6a
--- /dev/null
+++ b/net/netfilter/nft_synproxy.c
@@ -0,0 +1,298 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/types.h>
+#include <net/ip.h>
+#include <net/tcp.h>
+#include <net/netlink.h>
+#include <net/netfilter/nf_tables.h>
+#include <net/netfilter/nf_conntrack.h>
+#include <net/netfilter/nf_conntrack_synproxy.h>
+#include <net/netfilter/nf_synproxy.h>
+#include <linux/netfilter/nf_tables.h>
+#include <linux/netfilter/nf_synproxy.h>
+
+struct nft_synproxy {
+ struct nf_synproxy_info info;
+};
+
+static const struct nla_policy nft_synproxy_policy[NFTA_SYNPROXY_MAX + 1] = {
+ [NFTA_SYNPROXY_MSS] = { .type = NLA_U16 },
+ [NFTA_SYNPROXY_WSCALE] = { .type = NLA_U8 },
+ [NFTA_SYNPROXY_FLAGS] = { .type = NLA_U32 },
+};
+
+static void nft_synproxy_tcp_options(struct synproxy_options *opts,
+ const struct tcphdr *tcp,
+ struct synproxy_net *snet,
+ struct nf_synproxy_info *info,
+ struct nft_synproxy *priv)
+{
+ this_cpu_inc(snet->stats->syn_received);
+ if (tcp->ece && tcp->cwr)
+ opts->options |= NF_SYNPROXY_OPT_ECN;
+
+ opts->options &= priv->info.options;
+ if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP)
+ synproxy_init_timestamp_cookie(info, opts);
+ else
+ opts->options &= ~(NF_SYNPROXY_OPT_WSCALE |
+ NF_SYNPROXY_OPT_SACK_PERM |
+ NF_SYNPROXY_OPT_ECN);
+}
+
+static void nft_synproxy_eval_v4(const struct nft_expr *expr,
+ struct nft_regs *regs,
+ const struct nft_pktinfo *pkt,
+ const struct tcphdr *tcp,
+ struct tcphdr *_tcph,
+ struct synproxy_options *opts)
+{
+ struct nft_synproxy *priv = nft_expr_priv(expr);
+ struct nf_synproxy_info info = priv->info;
+ struct net *net = nft_net(pkt);
+ struct synproxy_net *snet = synproxy_pernet(net);
+ struct sk_buff *skb = pkt->skb;
+
+ if (tcp->syn) {
+ /* Initial SYN from client */
+ nft_synproxy_tcp_options(opts, tcp, snet, &info, priv);
+ synproxy_send_client_synack(net, skb, tcp, opts);
+ consume_skb(skb);
+ regs->verdict.code = NF_STOLEN;
+ return;
+ } else if (tcp->ack) {
+ /* ACK from client */
+ if (synproxy_recv_client_ack(net, skb, tcp, opts,
+ ntohl(tcp->seq))) {
+ consume_skb(skb);
+ regs->verdict.code = NF_STOLEN;
+ } else {
+ regs->verdict.code = NF_DROP;
+ }
+ return;
+ }
+
+ regs->verdict.code = NFT_CONTINUE;
+}
+
+#if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
+static void nft_synproxy_eval_v6(const struct nft_expr *expr,
+ struct nft_regs *regs,
+ const struct nft_pktinfo *pkt,
+ const struct tcphdr *tcp,
+ struct tcphdr *_tcph,
+ struct synproxy_options *opts)
+{
+ struct nft_synproxy *priv = nft_expr_priv(expr);
+ struct nf_synproxy_info info = priv->info;
+ struct net *net = nft_net(pkt);
+ struct synproxy_net *snet = synproxy_pernet(net);
+ struct sk_buff *skb = pkt->skb;
+
+ if (tcp->syn) {
+ /* Initial SYN from client */
+ nft_synproxy_tcp_options(opts, tcp, snet, &info, priv);
+ synproxy_send_client_synack_ipv6(net, skb, tcp, opts);
+ consume_skb(skb);
+ regs->verdict.code = NF_STOLEN;
+ return;
+ } else if (tcp->ack) {
+ /* ACK from client */
+ if (synproxy_recv_client_ack_ipv6(net, skb, tcp, opts,
+ ntohl(tcp->seq))) {
+ consume_skb(skb);
+ regs->verdict.code = NF_STOLEN;
+ } else {
+ regs->verdict.code = NF_DROP;
+ }
+ return;
+ }
+
+ regs->verdict.code = NFT_CONTINUE;
+}
+#endif /* CONFIG_NF_TABLES_IPV6*/
+
+static void nft_synproxy_eval(const struct nft_expr *expr,
+ struct nft_regs *regs,
+ const struct nft_pktinfo *pkt)
+{
+ struct synproxy_options opts = {};
+ struct sk_buff *skb = pkt->skb;
+ int thoff = pkt->xt.thoff;
+ const struct tcphdr *tcp;
+ struct tcphdr _tcph;
+
+ tcp = skb_header_pointer(skb, pkt->xt.thoff,
+ sizeof(struct tcphdr),
+ &_tcph);
+ if (pkt->tprot != IPPROTO_TCP) {
+ regs->verdict.code = NFT_BREAK;
+ return;
+ }
+
+ if (nf_ip_checksum(skb, nft_hook(pkt), thoff, IPPROTO_TCP)) {
+ regs->verdict.code = NF_DROP;
+ return;
+ }
+
+ if (!tcp) {
+ regs->verdict.code = NF_DROP;
+ return;
+ }
+
+ if (!synproxy_parse_options(skb, thoff, tcp, &opts)) {
+ regs->verdict.code = NF_DROP;
+ return;
+ }
+
+ switch (skb->protocol) {
+ case htons(ETH_P_IP):
+ nft_synproxy_eval_v4(expr, regs, pkt, tcp, &_tcph, &opts);
+ return;
+#if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
+ case htons(ETH_P_IPV6):
+ nft_synproxy_eval_v6(expr, regs, pkt, tcp, &_tcph, &opts);
+ return;
+#endif
+ }
+ regs->verdict.code = NFT_BREAK;
+}
+
+static int nft_synproxy_init(const struct nft_ctx *ctx,
+ const struct nft_expr *expr,
+ const struct nlattr * const tb[])
+{
+ struct synproxy_net *snet = synproxy_pernet(ctx->net);
+ struct nft_synproxy *priv = nft_expr_priv(expr);
+ u32 flags;
+ int err;
+
+ if (tb[NFTA_SYNPROXY_MSS])
+ priv->info.mss = ntohs(nla_get_be16(tb[NFTA_SYNPROXY_MSS]));
+ if (tb[NFTA_SYNPROXY_WSCALE])
+ priv->info.wscale = nla_get_u8(tb[NFTA_SYNPROXY_WSCALE]);
+ if (tb[NFTA_SYNPROXY_FLAGS]) {
+ flags = ntohl(nla_get_be32(tb[NFTA_SYNPROXY_FLAGS]));
+ if (flags != 0 && (flags & NF_SYNPROXY_OPT_MASK) == 0)
+ return -EINVAL;
+ priv->info.options = flags;
+ }
+
+ err = nf_ct_netns_get(ctx->net, ctx->family);
+ if (err)
+ return err;
+
+ switch (ctx->family) {
+ case NFPROTO_IPV4:
+ err = nf_synproxy_ipv4_init(snet, ctx->net);
+ if (err)
+ goto nf_ct_failure;
+ snet->hook_ref4++;
+ break;
+#if IS_ENABLED(CONFIG_IPV6)
+ case NFPROTO_IPV6:
+ err = nf_synproxy_ipv6_init(snet, ctx->net);
+ if (err)
+ goto nf_ct_failure;
+ snet->hook_ref6++;
+ break;
+ case NFPROTO_INET:
+ case NFPROTO_BRIDGE:
+ err = nf_synproxy_ipv4_init(snet, ctx->net);
+ if (err)
+ goto nf_ct_failure;
+ err = nf_synproxy_ipv6_init(snet, ctx->net);
+ if (err)
+ goto nf_ct_failure;
+ snet->hook_ref4++;
+ snet->hook_ref6++;
+ break;
+#endif
+ }
+
+ return 0;
+
+nf_ct_failure:
+ nf_ct_netns_put(ctx->net, ctx->family);
+ return err;
+}
+
+static void nft_synproxy_destroy(const struct nft_ctx *ctx,
+ const struct nft_expr *expr)
+{
+ struct synproxy_net *snet = synproxy_pernet(ctx->net);
+
+ switch (ctx->family) {
+ case NFPROTO_IPV4:
+ nf_synproxy_ipv4_fini(snet, ctx->net);
+ break;
+#if IS_ENABLED(CONFIG_IPV6)
+ case NFPROTO_IPV6:
+ nf_synproxy_ipv6_fini(snet, ctx->net);
+ break;
+ case NFPROTO_INET:
+ nf_synproxy_ipv4_fini(snet, ctx->net);
+ nf_synproxy_ipv6_fini(snet, ctx->net);
+ break;
+#endif
+ }
+ nf_ct_netns_put(ctx->net, ctx->family);
+}
+
+static int nft_synproxy_dump(struct sk_buff *skb, const struct nft_expr *expr)
+{
+ const struct nft_synproxy *priv = nft_expr_priv(expr);
+
+ if (nla_put_be16(skb, NFTA_SYNPROXY_MSS, ntohs(priv->info.mss)) ||
+ nla_put_u8(skb, NFTA_SYNPROXY_WSCALE, priv->info.wscale) ||
+ nla_put_be32(skb, NFTA_SYNPROXY_FLAGS, ntohl(priv->info.options)))
+ goto nla_put_failure;
+
+ return 0;
+
+nla_put_failure:
+ return -1;
+}
+
+static int nft_synproxy_validate(const struct nft_ctx *ctx,
+ const struct nft_expr *expr,
+ const struct nft_data **data)
+{
+ return nft_chain_validate_hooks(ctx->chain, (1 << NF_INET_LOCAL_IN) |
+ (1 << NF_INET_FORWARD));
+}
+
+static struct nft_expr_type nft_synproxy_type;
+static const struct nft_expr_ops nft_synproxy_ops = {
+ .eval = nft_synproxy_eval,
+ .size = NFT_EXPR_SIZE(sizeof(struct nft_synproxy)),
+ .init = nft_synproxy_init,
+ .destroy = nft_synproxy_destroy,
+ .dump = nft_synproxy_dump,
+ .type = &nft_synproxy_type,
+ .validate = nft_synproxy_validate,
+};
+
+static struct nft_expr_type nft_synproxy_type __read_mostly = {
+ .ops = &nft_synproxy_ops,
+ .name = "synproxy",
+ .owner = THIS_MODULE,
+ .policy = nft_synproxy_policy,
+ .maxattr = NFTA_OSF_MAX,
+};
+
+static int __init nft_synproxy_module_init(void)
+{
+ return nft_register_expr(&nft_synproxy_type);
+}
+
+static void __exit nft_synproxy_module_exit(void)
+{
+ return nft_unregister_expr(&nft_synproxy_type);
+}
+
+module_init(nft_synproxy_module_init);
+module_exit(nft_synproxy_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Fernando Fernandez <ffmancera@xxxxxxxxxx>");
+MODULE_ALIAS_NFT_EXPR("synproxy");
--
2.20.1
