netfilter: nf_tables: add number generator expression

This patch adds the numgen expression that allows us to generated
incremental and random numbers, this generator is bound to a upper limit
that is specified by userspace.

This expression is useful to distribute packets in a round-robin fashion
as well as randomly.

Signed-off-by: Laura Garcia Liebana <nevola@gmail.com>
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 784fbf15ab3de7f7f8fc5e690478dc294a293689..8c9d6ff70ec0c25496a821e50554fe53777f6cf7 100644 (file)
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -1121,4 +1121,28 @@ enum nft_trace_types {
        __NFT_TRACETYPE_MAX
 };
 #define NFT_TRACETYPE_MAX (__NFT_TRACETYPE_MAX - 1)
+
+/**
+ * enum nft_ng_attributes - nf_tables number generator expression netlink attributes
+ *
+ * @NFTA_NG_DREG: destination register (NLA_U32)
+ * @NFTA_NG_UNTIL: source value to increment the counter until reset (NLA_U32)
+ * @NFTA_NG_TYPE: operation type (NLA_U32)
+ */
+enum nft_ng_attributes {
+       NFTA_NG_UNSPEC,
+       NFTA_NG_DREG,
+       NFTA_NG_UNTIL,
+       NFTA_NG_TYPE,
+       __NFTA_NG_MAX
+};
+#define NFTA_NG_MAX    (__NFTA_NG_MAX - 1)
+
+enum nft_ng_types {
+       NFT_NG_INCREMENTAL,
+       NFT_NG_RANDOM,
+       __NFT_NG_MAX
+};
+#define NFT_NG_MAX     (__NFT_NG_MAX - 1)
+
 #endif /* _LINUX_NF_TABLES_H */

diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index 29a8078deafa43db82fb3c817d20c0f771b95801..e8d56d9a4df2cc2d92ebeb397aadd9869982c0cd 100644 (file)
--- 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_NUMGEN
+       tristate "Netfilter nf_tables number generator module"
+       help
+         This option adds the number generator expression used to perform
+         incremental counting and random numbers bound to a upper limit.
+
 config NFT_CT
        depends on NF_CONNTRACK
        tristate "Netfilter nf_tables conntrack module"

diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index 0fc42df19b8cf8d43fec4771db1776c13f39888f..0c8581100ac62bfa6ea39c1a7cc3b05406611b55 100644 (file)
--- 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-$(CONFIG_NFT_NUMGEN)       += nft_numgen.o
 obj-$(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_numgen.c b/net/netfilter/nft_numgen.c
new file mode 100644 (file)
index 0000000..176e26d
--- /dev/null
+++ b/net/netfilter/nft_numgen.c
@@ -0,0 +1,192 @@
+/*
+ * Copyright (c) 2016 Laura Garcia <nevola@gmail.com>
+ *
+ * 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/static_key.h>
+#include <net/netfilter/nf_tables.h>
+#include <net/netfilter/nf_tables_core.h>
+
+static DEFINE_PER_CPU(struct rnd_state, nft_numgen_prandom_state);
+
+struct nft_ng_inc {
+       enum nft_registers      dreg:8;
+       u32                     until;
+       atomic_t                counter;
+};
+
+static void nft_ng_inc_eval(const struct nft_expr *expr,
+                           struct nft_regs *regs,
+                           const struct nft_pktinfo *pkt)
+{
+       struct nft_ng_inc *priv = nft_expr_priv(expr);
+       u32 nval, oval;
+
+       do {
+               oval = atomic_read(&priv->counter);
+               nval = (oval + 1 < priv->until) ? oval + 1 : 0;
+       } while (atomic_cmpxchg(&priv->counter, oval, nval) != oval);
+
+       memcpy(&regs->data[priv->dreg], &priv->counter, sizeof(u32));
+}
+
+static const struct nla_policy nft_ng_policy[NFTA_NG_MAX + 1] = {
+       [NFTA_NG_DREG]          = { .type = NLA_U32 },
+       [NFTA_NG_UNTIL]         = { .type = NLA_U32 },
+       [NFTA_NG_TYPE]          = { .type = NLA_U32 },
+};
+
+static int nft_ng_inc_init(const struct nft_ctx *ctx,
+                          const struct nft_expr *expr,
+                          const struct nlattr * const tb[])
+{
+       struct nft_ng_inc *priv = nft_expr_priv(expr);
+
+       priv->until = ntohl(nla_get_be32(tb[NFTA_NG_UNTIL]));
+       if (priv->until == 0)
+               return -ERANGE;
+
+       priv->dreg = nft_parse_register(tb[NFTA_NG_DREG]);
+       atomic_set(&priv->counter, 0);
+
+       return nft_validate_register_store(ctx, priv->dreg, NULL,
+                                          NFT_DATA_VALUE, sizeof(u32));
+}
+
+static int nft_ng_dump(struct sk_buff *skb, enum nft_registers dreg,
+                      u32 until, enum nft_ng_types type)
+{
+       if (nft_dump_register(skb, NFTA_NG_DREG, dreg))
+               goto nla_put_failure;
+       if (nft_dump_register(skb, NFTA_NG_UNTIL, until))
+               goto nla_put_failure;
+       if (nft_dump_register(skb, NFTA_NG_TYPE, type))
+               goto nla_put_failure;
+
+       return 0;
+
+nla_put_failure:
+       return -1;
+}
+
+static int nft_ng_inc_dump(struct sk_buff *skb, const struct nft_expr *expr)
+{
+       const struct nft_ng_inc *priv = nft_expr_priv(expr);
+
+       return nft_ng_dump(skb, priv->dreg, priv->until, NFT_NG_INCREMENTAL);
+}
+
+struct nft_ng_random {
+       enum nft_registers      dreg:8;
+       u32                     until;
+};
+
+static void nft_ng_random_eval(const struct nft_expr *expr,
+                              struct nft_regs *regs,
+                              const struct nft_pktinfo *pkt)
+{
+       struct nft_ng_random *priv = nft_expr_priv(expr);
+       struct rnd_state *state = this_cpu_ptr(&nft_numgen_prandom_state);
+
+       regs->data[priv->dreg] = reciprocal_scale(prandom_u32_state(state),
+                                                 priv->until);
+}
+
+static int nft_ng_random_init(const struct nft_ctx *ctx,
+                             const struct nft_expr *expr,
+                             const struct nlattr * const tb[])
+{
+       struct nft_ng_random *priv = nft_expr_priv(expr);
+
+       priv->until = ntohl(nla_get_be32(tb[NFTA_NG_UNTIL]));
+       if (priv->until == 0)
+               return -ERANGE;
+
+       prandom_init_once(&nft_numgen_prandom_state);
+
+       priv->dreg = nft_parse_register(tb[NFTA_NG_DREG]);
+
+       return nft_validate_register_store(ctx, priv->dreg, NULL,
+                                          NFT_DATA_VALUE, sizeof(u32));
+}
+
+static int nft_ng_random_dump(struct sk_buff *skb, const struct nft_expr *expr)
+{
+       const struct nft_ng_random *priv = nft_expr_priv(expr);
+
+       return nft_ng_dump(skb, priv->dreg, priv->until, NFT_NG_RANDOM);
+}
+
+static struct nft_expr_type nft_ng_type;
+static const struct nft_expr_ops nft_ng_inc_ops = {
+       .type           = &nft_ng_type,
+       .size           = NFT_EXPR_SIZE(sizeof(struct nft_ng_inc)),
+       .eval           = nft_ng_inc_eval,
+       .init           = nft_ng_inc_init,
+       .dump           = nft_ng_inc_dump,
+};
+
+static const struct nft_expr_ops nft_ng_random_ops = {
+       .type           = &nft_ng_type,
+       .size           = NFT_EXPR_SIZE(sizeof(struct nft_ng_random)),
+       .eval           = nft_ng_random_eval,
+       .init           = nft_ng_random_init,
+       .dump           = nft_ng_random_dump,
+};
+
+static const struct nft_expr_ops *
+nft_ng_select_ops(const struct nft_ctx *ctx, const struct nlattr * const tb[])
+{
+       u32 type;
+
+       if (!tb[NFTA_NG_DREG]   ||
+           !tb[NFTA_NG_UNTIL]  ||
+           !tb[NFTA_NG_TYPE])
+               return ERR_PTR(-EINVAL);
+
+       type = ntohl(nla_get_be32(tb[NFTA_NG_TYPE]));
+
+       switch (type) {
+       case NFT_NG_INCREMENTAL:
+               return &nft_ng_inc_ops;
+       case NFT_NG_RANDOM:
+               return &nft_ng_random_ops;
+       }
+
+       return ERR_PTR(-EINVAL);
+}
+
+static struct nft_expr_type nft_ng_type __read_mostly = {
+       .name           = "numgen",
+       .select_ops     = &nft_ng_select_ops,
+       .policy         = nft_ng_policy,
+       .maxattr        = NFTA_NG_MAX,
+       .owner          = THIS_MODULE,
+};
+
+static int __init nft_ng_module_init(void)
+{
+       return nft_register_expr(&nft_ng_type);
+}
+
+static void __exit nft_ng_module_exit(void)
+{
+       nft_unregister_expr(&nft_ng_type);
+}
+
+module_init(nft_ng_module_init);
+module_exit(nft_ng_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Laura Garcia <nevola@gmail.com>");
+MODULE_ALIAS_NFT_EXPR("numgen");