Commit 91721c2d authored by Daniel Xu's avatar Daniel Xu Committed by Alexei Starovoitov
Browse files

netfilter: bpf: Support BPF_F_NETFILTER_IP_DEFRAG in netfilter link 



This commit adds support for enabling IP defrag using pre-existing
netfilter defrag support. Basically all the flag does is bump a refcnt
while the link the active. Checks are also added to ensure the prog
requesting defrag support is run _after_ netfilter defrag hooks.

We also take care to avoid any issues w.r.t. module unloading -- while
defrag is active on a link, the module is prevented from unloading.

Signed-off-by: default avatarDaniel Xu <dxu@dxuuu.xyz>
Reviewed-by: default avatarFlorian Westphal <fw@strlen.de>
Link: https://lore.kernel.org/r/5cff26f97e55161b7d56b09ddcf5f8888a5add1d.1689970773.git.dxu@dxuuu.xyz


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 9abddac5

include/uapi/linux/bpf.h

+5 −0
Original line number Diff line number Diff line
@@ -1188,6 +1188,11 @@ enum bpf_perf_event_type { 
 */

#define BPF_F_KPROBE_MULTI_RETURN	(1U << 0)



/* link_create.netfilter.flags used in LINK_CREATE command for

 * BPF_PROG_TYPE_NETFILTER to enable IP packet defragmentation.

 */

#define BPF_F_NETFILTER_IP_DEFRAG (1U << 0)



/* When BPF ldimm64's insn[0].src_reg != 0 then this can have

 * the following extensions:

 *

net/netfilter/nf_bpf_link.c

+108 −15
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

#include <linux/bpf.h>

#include <linux/filter.h>

#include <linux/kmod.h>

#include <linux/module.h>

#include <linux/netfilter.h>



#include <net/netfilter/nf_bpf_link.h>
@@ -23,8 +25,88 @@ struct bpf_nf_link { 
	struct nf_hook_ops hook_ops;

	struct net *net;

	u32 dead;

	const struct nf_defrag_hook *defrag_hook;

};



static const struct nf_defrag_hook *

get_proto_defrag_hook(struct bpf_nf_link *link,

		      const struct nf_defrag_hook __rcu *global_hook,

		      const char *mod)

{

	const struct nf_defrag_hook *hook;

	int err;



	/* RCU protects us from races against module unloading */

	rcu_read_lock();

	hook = rcu_dereference(global_hook);

	if (!hook) {

		rcu_read_unlock();

		err = request_module(mod);

		if (err)

			return ERR_PTR(err < 0 ? err : -EINVAL);



		rcu_read_lock();

		hook = rcu_dereference(global_hook);

	}



	if (hook && try_module_get(hook->owner)) {

		/* Once we have a refcnt on the module, we no longer need RCU */

		hook = rcu_pointer_handoff(hook);

	} else {

		WARN_ONCE(!hook, "%s has bad registration", mod);

		hook = ERR_PTR(-ENOENT);

	}

	rcu_read_unlock();



	if (!IS_ERR(hook)) {

		err = hook->enable(link->net);

		if (err) {

			module_put(hook->owner);

			hook = ERR_PTR(err);

		}

	}



	return hook;

}



static int bpf_nf_enable_defrag(struct bpf_nf_link *link)

{

	const struct nf_defrag_hook __maybe_unused *hook;



	switch (link->hook_ops.pf) {

#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV4)

	case NFPROTO_IPV4:

		hook = get_proto_defrag_hook(link, nf_defrag_v4_hook, "nf_defrag_ipv4");

		if (IS_ERR(hook))

			return PTR_ERR(hook);



		link->defrag_hook = hook;

		return 0;

#endif

#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)

	case NFPROTO_IPV6:

		hook = get_proto_defrag_hook(link, nf_defrag_v6_hook, "nf_defrag_ipv6");

		if (IS_ERR(hook))

			return PTR_ERR(hook);



		link->defrag_hook = hook;

		return 0;

#endif

	default:

		return -EAFNOSUPPORT;

	}

}



static void bpf_nf_disable_defrag(struct bpf_nf_link *link)

{

	const struct nf_defrag_hook *hook = link->defrag_hook;



	if (!hook)

		return;

	hook->disable(link->net);

	module_put(hook->owner);

}



static void bpf_nf_link_release(struct bpf_link *link)

{

	struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);
@@ -32,11 +114,11 @@ static void bpf_nf_link_release(struct bpf_link *link) 
	if (nf_link->dead)

		return;



	/* prevent hook-not-found warning splat from netfilter core when

	 * .detach was already called

	 */

	if (!cmpxchg(&nf_link->dead, 0, 1))

	/* do not double release in case .detach was already called */

	if (!cmpxchg(&nf_link->dead, 0, 1)) {

		nf_unregister_net_hook(nf_link->net, &nf_link->hook_ops);

		bpf_nf_disable_defrag(nf_link);

	}

}



static void bpf_nf_link_dealloc(struct bpf_link *link)
@@ -92,6 +174,8 @@ static const struct bpf_link_ops bpf_nf_link_lops = { 


static int bpf_nf_check_pf_and_hooks(const union bpf_attr *attr)

{

	int prio;



	switch (attr->link_create.netfilter.pf) {

	case NFPROTO_IPV4:

	case NFPROTO_IPV6:
@@ -102,19 +186,18 @@ static int bpf_nf_check_pf_and_hooks(const union bpf_attr *attr) 
		return -EAFNOSUPPORT;

	}



	if (attr->link_create.netfilter.flags)

	if (attr->link_create.netfilter.flags & ~BPF_F_NETFILTER_IP_DEFRAG)

		return -EOPNOTSUPP;



	/* make sure conntrack confirm is always last.

	 *

	 * In the future, if userspace can e.g. request defrag, then

	 * "defrag_requested && prio before NF_IP_PRI_CONNTRACK_DEFRAG"

	 * should fail.

	 */

	switch (attr->link_create.netfilter.priority) {

	case NF_IP_PRI_FIRST: return -ERANGE; /* sabotage_in and other warts */

	case NF_IP_PRI_LAST: return -ERANGE; /* e.g. conntrack confirm */

	}

	/* make sure conntrack confirm is always last */

	prio = attr->link_create.netfilter.priority;

	if (prio == NF_IP_PRI_FIRST)

		return -ERANGE;  /* sabotage_in and other warts */

	else if (prio == NF_IP_PRI_LAST)

		return -ERANGE;  /* e.g. conntrack confirm */

	else if ((attr->link_create.netfilter.flags & BPF_F_NETFILTER_IP_DEFRAG) &&

		 prio <= NF_IP_PRI_CONNTRACK_DEFRAG)

		return -ERANGE;  /* cannot use defrag if prog runs before nf_defrag */



	return 0;

}
@@ -149,6 +232,7 @@ int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog) 


	link->net = net;

	link->dead = false;

	link->defrag_hook = NULL;



	err = bpf_link_prime(&link->link, &link_primer);

	if (err) {
@@ -156,8 +240,17 @@ int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog) 
		return err;

	}



	if (attr->link_create.netfilter.flags & BPF_F_NETFILTER_IP_DEFRAG) {

		err = bpf_nf_enable_defrag(link);

		if (err) {

			bpf_link_cleanup(&link_primer);

			return err;

		}

	}



	err = nf_register_net_hook(net, &link->hook_ops);

	if (err) {

		bpf_nf_disable_defrag(link);

		bpf_link_cleanup(&link_primer);

		return err;

	}

tools/include/uapi/linux/bpf.h

+5 −0
Original line number Diff line number Diff line
@@ -1188,6 +1188,11 @@ enum bpf_perf_event_type { 
 */

#define BPF_F_KPROBE_MULTI_RETURN	(1U << 0)



/* link_create.netfilter.flags used in LINK_CREATE command for

 * BPF_PROG_TYPE_NETFILTER to enable IP packet defragmentation.

 */

#define BPF_F_NETFILTER_IP_DEFRAG (1U << 0)



/* When BPF ldimm64's insn[0].src_reg != 0 then this can have

 * the following extensions:

 *