Add support for the nth expression in netfilter. A nft_nth structure is created with dreg (to store the result into a given register), data (a nft_data structure to store the input value, it must be > 0), every (to store the data) and counter (to store atomically the current value).
Signed-off-by: Laura Garcia Liebana <nevola@xxxxxxxxx>
---
include/net/netfilter/nft_nth.h | 31 +++++++
include/uapi/linux/netfilter/nf_tables.h | 15 ++++
net/netfilter/Kconfig | 6 ++
net/netfilter/Makefile | 1 +
net/netfilter/nft_nth.c | 145 +++++++++++++++++++++++++++++++
5 files changed, 198 insertions(+)
create mode 100644 include/net/netfilter/nft_nth.h
create mode 100644 net/netfilter/nft_nth.c
diff --git a/include/net/netfilter/nft_nth.h b/include/net/netfilter/nft_nth.h
new file mode 100644
index 0000000..0d8788d
--- /dev/null
+++ b/include/net/netfilter/nft_nth.h
@@ -0,0 +1,31 @@
+#ifndef _NFT_NTH_H_
+#define _NFT_NTH_H_
+
+struct nft_nth {
+ enum nft_registers dreg:8;
+ struct nft_data data;
+ u32 every;
+ struct nft_nth_priv *master __attribute__((aligned(8)));
+};
+
+struct nft_nth_priv {
+ atomic_t counter;
+} ____cacheline_aligned_in_smp;
+
+extern const struct nla_policy nft_nth_policy[];
+
+int nft_nth_init(const struct nft_ctx *ctx,
+ const struct nft_expr *expr,
+ const struct nlattr * const tb[]);
+
+int nft_nth_dump(struct sk_buff *skb,
+ const struct nft_expr *expr);
+
+void nft_nth_eval(const struct nft_expr *expr,
+ struct nft_regs *regs,
+ const struct nft_pktinfo *pkt);
+
+void nft_nth_destroy(const struct nft_ctx *ctx,
+ const struct nft_expr *expr);
+
+#endif
diff --git a/include/uapi/linux/netfilter/nf_tables.h b/include/uapi/linux/netfilter/nf_tables.h
index 6a4dbe0..5ba075a 100644
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -1076,4 +1076,19 @@ enum nft_trace_types {
__NFT_TRACETYPE_MAX
};
#define NFT_TRACETYPE_MAX (__NFT_TRACETYPE_MAX - 1)
+
+/**
+ * enum nft_nth_attributes - nf_tables nth expression netlink attributes
+ * @NFTA_NTH_UNSPEC: unspecified attribute
+ * @NFTA_NTH_DREG: destination register (NLA_U32)
+ * @NFTA_NTH_DATA: source data (NLA_NESTED)
+ */
+enum nft_nth_attributes {
+ NFTA_NTH_UNSPEC,
+ NFTA_NTH_DREG,
+ NFTA_NTH_DATA,
+ __NFTA_NTH_MAX
+};
+#define NFTA_NTH_MAX (__NFTA_NTH_MAX - 1)
+
#endif /* _LINUX_NF_TABLES_H */
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index 95e757c..6f00d01 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -474,6 +474,12 @@ config NFT_META
This option adds the "meta" expression that you can use to match and
to set packet metainformation such as the packet mark.
+config NFT_NTH
+ tristate "Netfilter nf_tables nth module"
+ help
+ This option adds the "nth" expression that you can use to match a
+ packet every a specific given value.
+
config NFT_CT
depends on NF_CONNTRACK
tristate "Netfilter nf_tables conntrack module"
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index 6913454..2378f00 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -80,6 +80,7 @@ obj-$(CONFIG_NF_TABLES_NETDEV) += nf_tables_netdev.o
obj-$(CONFIG_NFT_COMPAT) += nft_compat.o
obj-$(CONFIG_NFT_EXTHDR) += nft_exthdr.o
obj-$(CONFIG_NFT_META) += nft_meta.o
+obj-$(CONFIG_NFT_NTH) += nft_nth.o
obj-$(CONFIG_NFT_CT) += nft_ct.o
obj-$(CONFIG_NFT_LIMIT) += nft_limit.o
obj-$(CONFIG_NFT_NAT) += nft_nat.o
diff --git a/net/netfilter/nft_nth.c b/net/netfilter/nft_nth.c
new file mode 100644
index 0000000..d0a5387
--- /dev/null
+++ b/net/netfilter/nft_nth.c
@@ -0,0 +1,145 @@
+/*
+ * Copyright (c) 2016 Laura Garcia <nevola@xxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/netlink.h>
+#include <linux/netfilter.h>
+#include <linux/netfilter/nf_tables.h>
+#include <linux/in.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+#include <linux/smp.h>
+#include <linux/static_key.h>
+#include <net/netfilter/nf_tables.h>
+#include <net/netfilter/nf_tables_core.h>
+#include <net/netfilter/nft_nth.h>
+
+void nft_nth_eval(const struct nft_expr *expr,
+ struct nft_regs *regs,
+ const struct nft_pktinfo *pkt)
+{
+ struct nft_nth *nth = nft_expr_priv(expr);
+ u32 nval, oval;
+
+ do {
+ oval = atomic_read(&nth->master->counter);
+ nval = (oval+1 < nth->every) ? oval+1 : 0;
+ } while (atomic_cmpxchg(&nth->master->counter, oval, nval) != oval);
+
+ memcpy(®s->data[nth->dreg], &nth->master->counter, sizeof(u32));
+}
+EXPORT_SYMBOL_GPL(nft_nth_eval);
+
+const struct nla_policy nft_nth_policy[NFTA_NTH_MAX + 1] = {
+ [NFTA_NTH_DREG] = { .type = NLA_U32 },
+ [NFTA_NTH_DATA] = { .type = NLA_NESTED },
+};
+
+int nft_nth_init(const struct nft_ctx *ctx,
+ const struct nft_expr *expr,
+ const struct nlattr * const tb[])
+{
+ struct nft_nth *nth = nft_expr_priv(expr);
+ struct nft_data_desc desc;
+ int err = 0;
+
+ err = nft_data_init(NULL, &nth->data,
+ sizeof(nth->data), &desc,
+ tb[NFTA_NTH_DATA]);
+ if (err < 0)
+ goto err;
+
+ memcpy(&nth->every, &nth->data, sizeof(u32));
+ if (nth->every == 0)
+ return -EINVAL;
+
+ nth->dreg = nft_parse_register(tb[NFTA_NTH_DREG]);
+
+ nth->master = kzalloc(sizeof(*nth->master), GFP_KERNEL);
+ if (!nth->master)
+ return -ENOMEM;
+ atomic_set(&nth->master->counter, 0);
+
+err:
+ return err;
+}
+EXPORT_SYMBOL_GPL(nft_nth_init);
+
+int nft_nth_dump(struct sk_buff *skb,
+ const struct nft_expr *expr)
+{
+ const struct nft_nth *nth = nft_expr_priv(expr);
+
+ if (nft_dump_register(skb, NFTA_NTH_DREG, nth->dreg))
+ goto nla_put_failure;
+ if (nft_data_dump(skb, NFTA_NTH_DATA, &nth->data,
+ NFT_DATA_VALUE, sizeof(nth->data)) < 0)
+ goto nla_put_failure;
+
+ return 0;
+
+nla_put_failure:
+ return -1;
+}
+EXPORT_SYMBOL_GPL(nft_nth_dump);
+
+void nft_nth_destroy(const struct nft_ctx *ctx,
+ const struct nft_expr *expr)
+{
+ struct nft_nth *nth = nft_expr_priv(expr);
+
+ kfree(nth->master);
+}
+EXPORT_SYMBOL_GPL(nft_nth_destroy);
+
+static struct nft_expr_type nft_nth_type;
+static const struct nft_expr_ops nft_nth_ops = {
+ .type = &nft_nth_type,
+ .size = NFT_EXPR_SIZE(sizeof(struct nft_nth)),
+ .eval = nft_nth_eval,
+ .init = nft_nth_init,
+ .destroy = nft_nth_destroy,
+ .dump = nft_nth_dump,
+};
+
+static const struct nft_expr_ops *
+nft_nth_select_ops(const struct nft_ctx *ctx,
+ const struct nlattr * const tb[])
+{
+ if (!tb[NFTA_NTH_DREG] ||
+ !tb[NFTA_NTH_DATA])
+ return ERR_PTR(-EINVAL);
+
+ return &nft_nth_ops;
+}
+
+static struct nft_expr_type nft_nth_type __read_mostly = {
+ .name = "nth",
+ .select_ops = &nft_nth_select_ops,
+ .policy = nft_nth_policy,
+ .maxattr = NFTA_NTH_MAX,
+ .owner = THIS_MODULE,
+};
+
+static int __init nft_nth_module_init(void)
+{
+ return nft_register_expr(&nft_nth_type);
+}
+
+static void __exit nft_nth_module_exit(void)
+{
+ nft_unregister_expr(&nft_nth_type);
+}
+
+module_init(nft_nth_module_init);
+module_exit(nft_nth_module_exit);
+
+MODULE_LICENSE("GPL");
--
2.8.1
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