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/net/netfilter/nft_numgen.c b/net/netfilter/nft_numgen.c
new file mode 100644
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(®s->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");
