This nfnl subsystem allows to dump the list of all active netfiler hooks,
e.g. defrag, conntrack, nf/ip/arp/ip6tables and so on.
This helps to see what kind of features are currently enabled in
the network stack.
Sample output from nft tool using this infra:
$ nft list hook ip input
family ip hook input {
+0000000010 nft_do_chain_inet [nf_tables] # nft table firewalld INPUT
+0000000100 nf_nat_ipv4_local_in [nf_nat]
+2147483647 ipv4_confirm [nf_conntrack]
}
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
---
include/uapi/linux/netfilter/nfnetlink.h | 3 +-
include/uapi/linux/netfilter/nfnetlink_hook.h | 54 +++
net/netfilter/Kconfig | 9 +
net/netfilter/Makefile | 1 +
net/netfilter/nfnetlink_hook.c | 375 ++++++++++++++++++
5 files changed, 441 insertions(+), 1 deletion(-)
create mode 100644 include/uapi/linux/netfilter/nfnetlink_hook.h
create mode 100644 net/netfilter/nfnetlink_hook.c
diff --git a/include/uapi/linux/netfilter/nfnetlink.h b/include/uapi/linux/netfilter/nfnetlink.h
index 5bc960f220b3..6cd58cd2a6f0 100644
--- a/include/uapi/linux/netfilter/nfnetlink.h
+++ b/include/uapi/linux/netfilter/nfnetlink.h
@@ -60,7 +60,8 @@ struct nfgenmsg {
#define NFNL_SUBSYS_CTHELPER 9
#define NFNL_SUBSYS_NFTABLES 10
#define NFNL_SUBSYS_NFT_COMPAT 11
-#define NFNL_SUBSYS_COUNT 12
+#define NFNL_SUBSYS_HOOK 12
+#define NFNL_SUBSYS_COUNT 13
/* Reserved control nfnetlink messages */
#define NFNL_MSG_BATCH_BEGIN NLMSG_MIN_TYPE
diff --git a/include/uapi/linux/netfilter/nfnetlink_hook.h b/include/uapi/linux/netfilter/nfnetlink_hook.h
new file mode 100644
index 000000000000..d8ac8278571b
--- /dev/null
+++ b/include/uapi/linux/netfilter/nfnetlink_hook.h
@@ -0,0 +1,54 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _NFNL_HOOK_H_
+#define _NFNL_HOOK_H_
+
+enum nfnl_hook_msg_types {
+ NFNL_MSG_HOOK_GET,
+ NFNL_MSG_HOOK_MAX,
+};
+
+/**
+ * enum nfnl_hook_attributes - nf_tables netfilter hook netlink attributes
+ *
+ * @NFNLA_HOOK_HOOKNUM: netfilter hook number (NLA_U32)
+ * @NFNLAA_HOOK_PRIORITY: netfilter hook priority (NLA_U32)
+ * @NFNLA_HOOK_DEV: netdevice name (NLA_STRING)
+ * @NFNLA_HOOK_FUNCTION_NAME: hook function name (NLA_STRING)
+ * @NFNLA_HOOK_MODULE_NAME: kernel module that registered this hook (NLA_STRING)
+ * @NFNLA_HOOK_CHAIN_INFO: basechain hook metadata (NLA_NESTED)
+ */
+enum nfnl_hook_attributes {
+ NFNLA_HOOK_UNSPEC,
+ NFNLA_HOOK_HOOKNUM,
+ NFNLA_HOOK_PRIORITY,
+ NFNLA_HOOK_DEV,
+ NFNLA_HOOK_FUNCTION_NAME,
+ NFNLA_HOOK_MODULE_NAME,
+ NFNLA_HOOK_CHAIN_INFO,
+ __NFNLA_HOOK_MAX
+};
+#define NFNLA_HOOK_MAX (__NFNLA_HOOK_MAX - 1)
+
+/**
+ * enum nfnl_hook_chain_info_attributes - chain description
+ *
+ * NFNLA_HOOK_INFO_DESC: nft chain and table name (enum nft_table_attributes) (NLA_NESTED)
+ * NFNLA_HOOK_INFO_TYPE: chain type (enum nfnl_hook_chaintype) (NLA_U32)
+ */
+enum nfnl_hook_chain_info_attributes {
+ NFNLA_HOOK_INFO_UNSPEC,
+ NFNLA_HOOK_INFO_DESC,
+ NFNLA_HOOK_INFO_TYPE,
+ __NFNLA_HOOK_INFO_MAX,
+};
+#define NFNLA_HOOK_INFO_MAX (__NFNLA_HOOK_INFO_MAX - 1)
+
+/**
+ * enum nfnl_hook_chaintype - chain type
+ *
+ * @NFNL_HOOK_TYPE_NFTABLES nf_tables base chain
+ */
+enum nfnl_hook_chaintype {
+ NFNL_HOOK_TYPE_NFTABLES = 0x1,
+};
+#endif /* _NFNL_HOOK_H */
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index 172d74560632..c81321372198 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -19,6 +19,15 @@ config NETFILTER_FAMILY_BRIDGE
config NETFILTER_FAMILY_ARP
bool
+config NETFILTER_NETLINK_HOOK
+ tristate "Netfilter base hook dump support"
+ depends on NETFILTER_ADVANCED
+ select NETFILTER_NETLINK
+ help
+ If this option is enabled, the kernel will include support
+ to list the base netfilter hooks via NFNETLINK.
+ This is helpful for debugging.
+
config NETFILTER_NETLINK_ACCT
tristate "Netfilter NFACCT over NFNETLINK interface"
depends on NETFILTER_ADVANCED
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index e80e010354b1..87112dad1fd4 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -22,6 +22,7 @@ obj-$(CONFIG_NETFILTER_NETLINK_ACCT) += nfnetlink_acct.o
obj-$(CONFIG_NETFILTER_NETLINK_QUEUE) += nfnetlink_queue.o
obj-$(CONFIG_NETFILTER_NETLINK_LOG) += nfnetlink_log.o
obj-$(CONFIG_NETFILTER_NETLINK_OSF) += nfnetlink_osf.o
+obj-$(CONFIG_NETFILTER_NETLINK_HOOK) += nfnetlink_hook.o
# connection tracking
obj-$(CONFIG_NF_CONNTRACK) += nf_conntrack.o
diff --git a/net/netfilter/nfnetlink_hook.c b/net/netfilter/nfnetlink_hook.c
new file mode 100644
index 000000000000..04586dfa2acd
--- /dev/null
+++ b/net/netfilter/nfnetlink_hook.c
@@ -0,0 +1,375 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2021 Red Hat GmbH
+ *
+ * Author: Florian Westphal <fw@xxxxxxxxx>
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/skbuff.h>
+#include <linux/errno.h>
+#include <linux/netlink.h>
+#include <linux/slab.h>
+
+#include <linux/netfilter.h>
+
+#include <linux/netfilter/nfnetlink.h>
+#include <linux/netfilter/nfnetlink_hook.h>
+
+#include <net/netfilter/nf_tables.h>
+#include <net/sock.h>
+
+static const struct nla_policy nfnl_hook_nla_policy[NFNLA_HOOK_MAX + 1] = {
+ [NFNLA_HOOK_HOOKNUM] = { .type = NLA_U32 },
+ [NFNLA_HOOK_PRIORITY] = { .type = NLA_U32 },
+ [NFNLA_HOOK_DEV] = { .type = NLA_STRING,
+ .len = IFNAMSIZ - 1 },
+ [NFNLA_HOOK_FUNCTION_NAME] = { .type = NLA_NUL_STRING,
+ .len = KSYM_NAME_LEN, },
+ [NFNLA_HOOK_MODULE_NAME] = { .type = NLA_NUL_STRING,
+ .len = MODULE_NAME_LEN, },
+ [NFNLA_HOOK_CHAIN_INFO] = { .type = NLA_NESTED, },
+};
+
+static int nf_netlink_dump_start_rcu(struct sock *nlsk, struct sk_buff *skb,
+ const struct nlmsghdr *nlh,
+ struct netlink_dump_control *c)
+{
+ int err;
+
+ if (!try_module_get(THIS_MODULE))
+ return -EINVAL;
+
+ rcu_read_unlock();
+ err = netlink_dump_start(nlsk, skb, nlh, c);
+ rcu_read_lock();
+ module_put(THIS_MODULE);
+
+ return err;
+}
+
+struct nfnl_dump_hook_data {
+ char devname[IFNAMSIZ];
+ unsigned long headv;
+ u8 hook;
+};
+
+static int nfnl_hook_put_nft_chain_info(struct sk_buff *nlskb,
+ const struct nfnl_dump_hook_data *ctx,
+ unsigned int seq,
+ const struct nf_hook_ops *ops)
+{
+ struct net *net = sock_net(nlskb->sk);
+ struct nlattr *nest, *nest2;
+ struct nft_chain *chain;
+ int ret = 0;
+
+ if (ops->hook_ops_type != NF_HOOK_OP_NF_TABLES)
+ return 0;
+
+ chain = ops->priv;
+ if (WARN_ON_ONCE(!chain))
+ return 0;
+
+ if (!nft_is_active(net, chain))
+ return 0;
+
+ nest = nla_nest_start(nlskb, NFNLA_HOOK_CHAIN_INFO);
+ if (!nest)
+ return -EMSGSIZE;
+
+ ret = nla_put_be32(nlskb, NFNLA_HOOK_INFO_TYPE,
+ htonl(NFNL_HOOK_TYPE_NFTABLES));
+ if (ret)
+ goto cancel_nest;
+
+ nest2 = nla_nest_start(nlskb, NFNLA_HOOK_INFO_DESC);
+ if (!nest2)
+ goto cancel_nest;
+
+ ret = nla_put_string(nlskb, NFTA_CHAIN_TABLE, chain->table->name);
+ if (ret)
+ goto cancel_nest;
+
+ ret = nla_put_string(nlskb, NFTA_CHAIN_NAME, chain->name);
+ if (ret)
+ goto cancel_nest;
+
+ nla_nest_end(nlskb, nest2);
+ nla_nest_end(nlskb, nest);
+ return ret;
+
+cancel_nest:
+ nla_nest_cancel(nlskb, nest);
+ return -EMSGSIZE;
+}
+
+static int nfnl_hook_dump_one(struct sk_buff *nlskb,
+ const struct nfnl_dump_hook_data *ctx,
+ const struct nf_hook_ops *ops,
+ unsigned int seq)
+{
+ u16 event = nfnl_msg_type(NFNL_SUBSYS_HOOK, NFNL_MSG_HOOK_GET);
+ unsigned int portid = NETLINK_CB(nlskb).portid;
+ struct nlmsghdr *nlh;
+ int ret = -EMSGSIZE;
+#ifdef CONFIG_KALLSYMS
+ char sym[KSYM_SYMBOL_LEN];
+ char *module_name;
+#endif
+ nlh = nfnl_msg_put(nlskb, portid, seq, event,
+ NLM_F_MULTI, ops->pf, NFNETLINK_V0, 0);
+ if (!nlh)
+ goto nla_put_failure;
+
+#ifdef CONFIG_KALLSYMS
+ ret = snprintf(sym, sizeof(sym), "%ps", ops->hook);
+ if (ret < 0 || ret > (int)sizeof(sym))
+ goto nla_put_failure;
+
+ module_name = strstr(sym, " [");
+ if (module_name) {
+ char *end;
+
+ module_name += 2;
+ end = strchr(module_name, ']');
+ if (end) {
+ *end = 0;
+
+ ret = nla_put_string(nlskb, NFNLA_HOOK_MODULE_NAME, module_name);
+ if (ret)
+ goto nla_put_failure;
+ }
+ }
+
+ ret = nla_put_string(nlskb, NFNLA_HOOK_FUNCTION_NAME, sym);
+ if (ret)
+ goto nla_put_failure;
+#endif
+
+ ret = nla_put_be32(nlskb, NFNLA_HOOK_HOOKNUM, htonl(ops->hooknum));
+ if (ret)
+ goto nla_put_failure;
+
+ ret = nla_put_be32(nlskb, NFNLA_HOOK_PRIORITY, htonl(ops->priority));
+ if (ret)
+ goto nla_put_failure;
+
+ ret = nfnl_hook_put_nft_chain_info(nlskb, ctx, seq, ops);
+ if (ret)
+ goto nla_put_failure;
+
+ nlmsg_end(nlskb, nlh);
+ return 0;
+nla_put_failure:
+ nlmsg_trim(nlskb, nlh);
+ return ret;
+}
+
+static const struct nf_hook_entries *
+nfnl_hook_entries_head(u8 pf, unsigned int hook, struct net *net, const char *dev)
+{
+ const struct nf_hook_entries *hook_head = NULL;
+ struct net_device *netdev;
+
+ switch (pf) {
+ case NFPROTO_IPV4:
+ if (hook >= ARRAY_SIZE(net->nf.hooks_ipv4))
+ return ERR_PTR(-EINVAL);
+ hook_head = rcu_dereference(net->nf.hooks_ipv4[hook]);
+ break;
+ case NFPROTO_IPV6:
+ hook_head = rcu_dereference(net->nf.hooks_ipv6[hook]);
+ if (hook >= ARRAY_SIZE(net->nf.hooks_ipv6))
+ return ERR_PTR(-EINVAL);
+ break;
+ case NFPROTO_ARP:
+#ifdef CONFIG_NETFILTER_FAMILY_ARP
+ if (hook >= ARRAY_SIZE(net->nf.hooks_arp))
+ return ERR_PTR(-EINVAL);
+ hook_head = rcu_dereference(net->nf.hooks_arp[hook]);
+#endif
+ break;
+ case NFPROTO_BRIDGE:
+#ifdef CONFIG_NETFILTER_FAMILY_BRIDGE
+ if (hook >= ARRAY_SIZE(net->nf.hooks_bridge))
+ return ERR_PTR(-EINVAL);
+ hook_head = rcu_dereference(net->nf.hooks_bridge[hook]);
+#endif
+ break;
+#if IS_ENABLED(CONFIG_DECNET)
+ case NFPROTO_DECNET:
+ if (hook >= ARRAY_SIZE(net->nf.hooks_decnet))
+ return ERR_PTR(-EINVAL);
+ hook_head = rcu_dereference(net->nf.hooks_decnet[hook]);
+ break;
+#endif
+#ifdef CONFIG_NETFILTER_INGRESS
+ case NFPROTO_NETDEV:
+ if (hook != NF_NETDEV_INGRESS)
+ return ERR_PTR(-EOPNOTSUPP);
+
+ if (!dev)
+ return ERR_PTR(-ENODEV);
+
+ netdev = dev_get_by_name_rcu(net, dev);
+ if (!netdev)
+ return ERR_PTR(-ENODEV);
+
+ return rcu_dereference(netdev->nf_hooks_ingress);
+#endif
+ default:
+ return ERR_PTR(-EPROTONOSUPPORT);
+ }
+
+ return hook_head;
+}
+
+static int nfnl_hook_dump(struct sk_buff *nlskb,
+ struct netlink_callback *cb)
+{
+ struct nfgenmsg *nfmsg = nlmsg_data(cb->nlh);
+ struct nfnl_dump_hook_data *ctx = cb->data;
+ int err, family = nfmsg->nfgen_family;
+ struct net *net = sock_net(nlskb->sk);
+ struct nf_hook_ops * const *ops;
+ const struct nf_hook_entries *e;
+ unsigned int i = cb->args[0];
+
+ rcu_read_lock();
+
+ e = nfnl_hook_entries_head(family, ctx->hook, net, ctx->devname);
+ if (!e)
+ goto done;
+
+ if (IS_ERR(e)) {
+ cb->seq++;
+ goto done;
+ }
+
+ if ((unsigned long)e != ctx->headv || i >= e->num_hook_entries)
+ cb->seq++;
+
+ ops = nf_hook_entries_get_hook_ops(e);
+
+ for (; i < e->num_hook_entries; i++) {
+ err = nfnl_hook_dump_one(nlskb, ctx, ops[i], cb->seq);
+ if (err)
+ break;
+ }
+
+done:
+ nl_dump_check_consistent(cb, nlmsg_hdr(nlskb));
+ rcu_read_unlock();
+ cb->args[0] = i;
+ return nlskb->len;
+}
+
+static int nfnl_hook_dump_start(struct netlink_callback *cb)
+{
+ const struct nfgenmsg *nfmsg = nlmsg_data(cb->nlh);
+ const struct nlattr * const *nla = cb->data;
+ struct nfnl_dump_hook_data *ctx = NULL;
+ struct net *net = sock_net(cb->skb->sk);
+ u8 family = nfmsg->nfgen_family;
+ char name[IFNAMSIZ] = "";
+ const void *head;
+ u32 hooknum;
+
+ hooknum = ntohl(nla_get_be32(nla[NFNLA_HOOK_HOOKNUM]));
+ if (hooknum > 255)
+ return -EINVAL;
+
+ if (family == NFPROTO_NETDEV) {
+ if (!nla[NFNLA_HOOK_DEV])
+ return -EINVAL;
+
+ nla_strscpy(name, nla[NFNLA_HOOK_DEV], sizeof(name));
+ }
+
+ rcu_read_lock();
+ /* Not dereferenced; for consistency check only */
+ head = nfnl_hook_entries_head(family, hooknum, net, name);
+ rcu_read_unlock();
+
+ if (head && IS_ERR(head))
+ return PTR_ERR(head);
+
+ ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+ if (!ctx)
+ return -ENOMEM;
+
+ strscpy(ctx->devname, name, sizeof(ctx->devname));
+ ctx->headv = (unsigned long)head;
+ ctx->hook = hooknum;
+
+ cb->seq = 1;
+ cb->data = ctx;
+
+ return 0;
+}
+
+static int nfnl_hook_dump_stop(struct netlink_callback *cb)
+{
+ kfree(cb->data);
+ return 0;
+}
+
+static int nfnl_hook_get(struct sk_buff *skb,
+ const struct nfnl_info *info,
+ const struct nlattr * const nla[])
+{
+ if (!nla[NFNLA_HOOK_HOOKNUM])
+ return -EINVAL;
+
+ if (info->nlh->nlmsg_flags & NLM_F_DUMP) {
+ struct netlink_dump_control c = {
+ .start = nfnl_hook_dump_start,
+ .done = nfnl_hook_dump_stop,
+ .dump = nfnl_hook_dump,
+ .module = THIS_MODULE,
+ .data = (void *)nla,
+ };
+
+ return nf_netlink_dump_start_rcu(info->sk, skb, info->nlh, &c);
+ }
+
+ return -EOPNOTSUPP;
+}
+
+static const struct nfnl_callback nfnl_hook_cb[NFNL_MSG_HOOK_MAX] = {
+ [NFNL_MSG_HOOK_GET] = {
+ .call = nfnl_hook_get,
+ .type = NFNL_CB_RCU,
+ .attr_count = NFNLA_HOOK_MAX,
+ .policy = nfnl_hook_nla_policy
+ },
+};
+
+static const struct nfnetlink_subsystem nfhook_subsys = {
+ .name = "nfhook",
+ .subsys_id = NFNL_SUBSYS_HOOK,
+ .cb_count = NFNL_MSG_HOOK_MAX,
+ .cb = nfnl_hook_cb,
+};
+
+MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_HOOK);
+
+static int __init nfnetlink_hook_init(void)
+{
+ return nfnetlink_subsys_register(&nfhook_subsys);
+}
+
+static void __exit nfnetlink_hook_exit(void)
+{
+ nfnetlink_subsys_unregister(&nfhook_subsys);
+}
+
+module_init(nfnetlink_hook_init);
+module_exit(nfnetlink_hook_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Florian Westphal <fw@xxxxxxxxx>");
+MODULE_DESCRIPTION("nfnetlink_hook: list registered netfilter hooks");
--
2.26.3
