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From:   Daniel Xu <dxu@dxuuu.xyz>
To:     fw@strlen.de, davem@davemloft.net, pabeni@redhat.com,
        pablo@netfilter.org, dsahern@kernel.org, edumazet@google.com,
        kuba@kernel.org, kadlec@netfilter.org,
        alexei.starovoitov@gmail.com, daniel@iogearbox.net
Cc:     netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        bpf@vger.kernel.org
Subject: [PATCH bpf-next v4 1/6] netfilter: defrag: Add glue hooks for enabling/disabling defrag
Date:   Wed, 12 Jul 2023 17:43:56 -0600
Message-ID: <e948d8c93103b6c020cba1d697dc5cd63f9af5e5.1689203090.git.dxu@dxuuu.xyz>
In-Reply-To: <cover.1689203090.git.dxu@dxuuu.xyz>
References: <cover.1689203090.git.dxu@dxuuu.xyz>
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We want to be able to enable/disable IP packet defrag from core
bpf/netfilter code. In other words, execute code from core that could
possibly be built as a module.

To help avoid symbol resolution errors, use glue hooks that the modules
will register callbacks with during module init.

Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
---
 include/linux/netfilter.h                 | 12 ++++++++++++
 net/ipv4/netfilter/nf_defrag_ipv4.c       | 16 +++++++++++++++-
 net/ipv6/netfilter/nf_defrag_ipv6_hooks.c | 10 ++++++++++
 net/netfilter/core.c                      |  6 ++++++
 4 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/include/linux/netfilter.h b/include/linux/netfilter.h
index d4fed4c508ca..77a637b681f2 100644
--- a/include/linux/netfilter.h
+++ b/include/linux/netfilter.h
@@ -481,6 +481,18 @@ struct nfnl_ct_hook {
 };
 extern const struct nfnl_ct_hook __rcu *nfnl_ct_hook;
 
+struct nf_defrag_v4_hook {
+	int (*enable)(struct net *net);
+	void (*disable)(struct net *net);
+};
+extern const struct nf_defrag_v4_hook __rcu *nf_defrag_v4_hook;
+
+struct nf_defrag_v6_hook {
+	int (*enable)(struct net *net);
+	void (*disable)(struct net *net);
+};
+extern const struct nf_defrag_v6_hook __rcu *nf_defrag_v6_hook;
+
 /*
  * nf_skb_duplicated - TEE target has sent a packet
  *
diff --git a/net/ipv4/netfilter/nf_defrag_ipv4.c b/net/ipv4/netfilter/nf_defrag_ipv4.c
index e61ea428ea18..1f3e0e893b7a 100644
--- a/net/ipv4/netfilter/nf_defrag_ipv4.c
+++ b/net/ipv4/netfilter/nf_defrag_ipv4.c
@@ -7,6 +7,7 @@
 #include <linux/ip.h>
 #include <linux/netfilter.h>
 #include <linux/module.h>
+#include <linux/rcupdate.h>
 #include <linux/skbuff.h>
 #include <net/netns/generic.h>
 #include <net/route.h>
@@ -113,17 +114,30 @@ static void __net_exit defrag4_net_exit(struct net *net)
 	}
 }
 
+static const struct nf_defrag_v4_hook defrag_hook = {
+	.enable = nf_defrag_ipv4_enable,
+	.disable = nf_defrag_ipv4_disable,
+};
+
 static struct pernet_operations defrag4_net_ops = {
 	.exit = defrag4_net_exit,
 };
 
 static int __init nf_defrag_init(void)
 {
-	return register_pernet_subsys(&defrag4_net_ops);
+	int err;
+
+	err = register_pernet_subsys(&defrag4_net_ops);
+	if (err)
+		return err;
+
+	rcu_assign_pointer(nf_defrag_v4_hook, &defrag_hook);
+	return err;
 }
 
 static void __exit nf_defrag_fini(void)
 {
+	rcu_assign_pointer(nf_defrag_v4_hook, NULL);
 	unregister_pernet_subsys(&defrag4_net_ops);
 }
 
diff --git a/net/ipv6/netfilter/nf_defrag_ipv6_hooks.c b/net/ipv6/netfilter/nf_defrag_ipv6_hooks.c
index cb4eb1d2c620..f7c7ee31c472 100644
--- a/net/ipv6/netfilter/nf_defrag_ipv6_hooks.c
+++ b/net/ipv6/netfilter/nf_defrag_ipv6_hooks.c
@@ -10,6 +10,7 @@
 #include <linux/module.h>
 #include <linux/skbuff.h>
 #include <linux/icmp.h>
+#include <linux/rcupdate.h>
 #include <linux/sysctl.h>
 #include <net/ipv6_frag.h>
 
@@ -96,6 +97,11 @@ static void __net_exit defrag6_net_exit(struct net *net)
 	}
 }
 
+static const struct nf_defrag_v6_hook defrag_hook = {
+	.enable = nf_defrag_ipv6_enable,
+	.disable = nf_defrag_ipv6_disable,
+};
+
 static struct pernet_operations defrag6_net_ops = {
 	.exit = defrag6_net_exit,
 };
@@ -114,6 +120,9 @@ static int __init nf_defrag_init(void)
 		pr_err("nf_defrag_ipv6: can't register pernet ops\n");
 		goto cleanup_frag6;
 	}
+
+	rcu_assign_pointer(nf_defrag_v6_hook, &defrag_hook);
+
 	return ret;
 
 cleanup_frag6:
@@ -124,6 +133,7 @@ static int __init nf_defrag_init(void)
 
 static void __exit nf_defrag_fini(void)
 {
+	rcu_assign_pointer(nf_defrag_v6_hook, NULL);
 	unregister_pernet_subsys(&defrag6_net_ops);
 	nf_ct_frag6_cleanup();
 }
diff --git a/net/netfilter/core.c b/net/netfilter/core.c
index 5f76ae86a656..34845155bb85 100644
--- a/net/netfilter/core.c
+++ b/net/netfilter/core.c
@@ -680,6 +680,12 @@ EXPORT_SYMBOL_GPL(nfnl_ct_hook);
 const struct nf_ct_hook __rcu *nf_ct_hook __read_mostly;
 EXPORT_SYMBOL_GPL(nf_ct_hook);
 
+const struct nf_defrag_v4_hook __rcu *nf_defrag_v4_hook __read_mostly;
+EXPORT_SYMBOL_GPL(nf_defrag_v4_hook);
+
+const struct nf_defrag_v6_hook __rcu *nf_defrag_v6_hook __read_mostly;
+EXPORT_SYMBOL_GPL(nf_defrag_v6_hook);
+
 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
 u8 nf_ctnetlink_has_listener;
 EXPORT_SYMBOL_GPL(nf_ctnetlink_has_listener);
-- 
2.41.0