Commit 695c1214 authored by Jakub Sitnicki's avatar Jakub Sitnicki Committed by Alexei Starovoitov
Browse files

bpf, netns: Keep attached programs in bpf_prog_array 



Prepare for having multi-prog attachments for new netns attach types by
storing programs to run in a bpf_prog_array, which is well suited for
iterating over programs and running them in sequence.

After this change bpf(PROG_QUERY) may block to allocate memory in
bpf_prog_array_copy_to_user() for collected program IDs. This forces a
change in how we protect access to the attached program in the query
callback. Because bpf_prog_array_copy_to_user() can sleep, we switch from
an RCU read lock to holding a mutex that serializes updaters.

Because we allow only one BPF flow_dissector program to be attached to
netns at all times, the bpf_prog_array pointed by net->bpf.run_array is
always either detached (null) or one element long.

No functional changes intended.

Signed-off-by: default avatarJakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarMartin KaFai Lau <kafai@fb.com>
Acked-by: default avatarAndrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200625141357.910330-3-jakub@cloudflare.com
parent 3b701699

include/net/netns/bpf.h

+4 −1
Original line number Diff line number Diff line
@@ -9,9 +9,12 @@ 
#include <linux/bpf-netns.h>



struct bpf_prog;

struct bpf_prog_array;



struct netns_bpf {

	struct bpf_prog __rcu *progs[MAX_NETNS_BPF_ATTACH_TYPE];

	/* Array of programs to run compiled from progs or links */

	struct bpf_prog_array __rcu *run_array[MAX_NETNS_BPF_ATTACH_TYPE];

	struct bpf_prog *progs[MAX_NETNS_BPF_ATTACH_TYPE];

	struct bpf_link *links[MAX_NETNS_BPF_ATTACH_TYPE];

};

kernel/bpf/net_namespace.c

+82 −38
Original line number Diff line number Diff line
@@ -33,6 +33,17 @@ static void __net_exit bpf_netns_link_auto_detach(struct bpf_link *link) 
	net_link->net = NULL;

}



/* Must be called with netns_bpf_mutex held. */

static void netns_bpf_run_array_detach(struct net *net,

				       enum netns_bpf_attach_type type)

{

	struct bpf_prog_array *run_array;



	run_array = rcu_replace_pointer(net->bpf.run_array[type], NULL,

					lockdep_is_held(&netns_bpf_mutex));

	bpf_prog_array_free(run_array);

}



static void bpf_netns_link_release(struct bpf_link *link)

{

	struct bpf_netns_link *net_link =
@@ -54,8 +65,8 @@ static void bpf_netns_link_release(struct bpf_link *link) 
	if (!net)

		goto out_unlock;



	netns_bpf_run_array_detach(net, type);

	net->bpf.links[type] = NULL;

	RCU_INIT_POINTER(net->bpf.progs[type], NULL);



out_unlock:

	mutex_unlock(&netns_bpf_mutex);
@@ -76,6 +87,7 @@ static int bpf_netns_link_update_prog(struct bpf_link *link, 
	struct bpf_netns_link *net_link =

		container_of(link, struct bpf_netns_link, link);

	enum netns_bpf_attach_type type = net_link->netns_type;

	struct bpf_prog_array *run_array;

	struct net *net;

	int ret = 0;
@@ -93,8 +105,11 @@ static int bpf_netns_link_update_prog(struct bpf_link *link, 
		goto out_unlock;

	}



	run_array = rcu_dereference_protected(net->bpf.run_array[type],

					      lockdep_is_held(&netns_bpf_mutex));

	WRITE_ONCE(run_array->items[0].prog, new_prog);



	old_prog = xchg(&link->prog, new_prog);

	rcu_assign_pointer(net->bpf.progs[type], new_prog);

	bpf_prog_put(old_prog);



out_unlock:
@@ -142,14 +157,38 @@ static const struct bpf_link_ops bpf_netns_link_ops = { 
	.show_fdinfo = bpf_netns_link_show_fdinfo,

};



/* Must be called with netns_bpf_mutex held. */

static int __netns_bpf_prog_query(const union bpf_attr *attr,

				  union bpf_attr __user *uattr,

				  struct net *net,

				  enum netns_bpf_attach_type type)

{

	__u32 __user *prog_ids = u64_to_user_ptr(attr->query.prog_ids);

	struct bpf_prog_array *run_array;

	u32 prog_cnt = 0, flags = 0;



	run_array = rcu_dereference_protected(net->bpf.run_array[type],

					      lockdep_is_held(&netns_bpf_mutex));

	if (run_array)

		prog_cnt = bpf_prog_array_length(run_array);



	if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags)))

		return -EFAULT;

	if (copy_to_user(&uattr->query.prog_cnt, &prog_cnt, sizeof(prog_cnt)))

		return -EFAULT;

	if (!attr->query.prog_cnt || !prog_ids || !prog_cnt)

		return 0;



	return bpf_prog_array_copy_to_user(run_array, prog_ids,

					   attr->query.prog_cnt);

}



int netns_bpf_prog_query(const union bpf_attr *attr,

			 union bpf_attr __user *uattr)

{

	__u32 __user *prog_ids = u64_to_user_ptr(attr->query.prog_ids);

	u32 prog_id, prog_cnt = 0, flags = 0;

	enum netns_bpf_attach_type type;

	struct bpf_prog *attached;

	struct net *net;

	int ret;



	if (attr->query.query_flags)

		return -EINVAL;
@@ -162,32 +201,17 @@ int netns_bpf_prog_query(const union bpf_attr *attr, 
	if (IS_ERR(net))

		return PTR_ERR(net);



	rcu_read_lock();

	attached = rcu_dereference(net->bpf.progs[type]);

	if (attached) {

		prog_cnt = 1;

		prog_id = attached->aux->id;

	}

	rcu_read_unlock();

	mutex_lock(&netns_bpf_mutex);

	ret = __netns_bpf_prog_query(attr, uattr, net, type);

	mutex_unlock(&netns_bpf_mutex);



	put_net(net);



	if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags)))

		return -EFAULT;

	if (copy_to_user(&uattr->query.prog_cnt, &prog_cnt, sizeof(prog_cnt)))

		return -EFAULT;



	if (!attr->query.prog_cnt || !prog_ids || !prog_cnt)

		return 0;



	if (copy_to_user(prog_ids, &prog_id, sizeof(u32)))

		return -EFAULT;



	return 0;

	return ret;

}



int netns_bpf_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)

{

	struct bpf_prog_array *run_array;

	enum netns_bpf_attach_type type;

	struct bpf_prog *attached;

	struct net *net;
@@ -217,14 +241,28 @@ int netns_bpf_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog) 
	if (ret)

		goto out_unlock;



	attached = rcu_dereference_protected(net->bpf.progs[type],

					     lockdep_is_held(&netns_bpf_mutex));

	attached = net->bpf.progs[type];

	if (attached == prog) {

		/* The same program cannot be attached twice */

		ret = -EINVAL;

		goto out_unlock;

	}

	rcu_assign_pointer(net->bpf.progs[type], prog);



	run_array = rcu_dereference_protected(net->bpf.run_array[type],

					      lockdep_is_held(&netns_bpf_mutex));

	if (run_array) {

		WRITE_ONCE(run_array->items[0].prog, prog);

	} else {

		run_array = bpf_prog_array_alloc(1, GFP_KERNEL);

		if (!run_array) {

			ret = -ENOMEM;

			goto out_unlock;

		}

		run_array->items[0].prog = prog;

		rcu_assign_pointer(net->bpf.run_array[type], run_array);

	}



	net->bpf.progs[type] = prog;

	if (attached)

		bpf_prog_put(attached);
@@ -244,11 +282,11 @@ static int __netns_bpf_prog_detach(struct net *net, 
	if (net->bpf.links[type])

		return -EINVAL;



	attached = rcu_dereference_protected(net->bpf.progs[type],

					     lockdep_is_held(&netns_bpf_mutex));

	attached = net->bpf.progs[type];

	if (!attached)

		return -ENOENT;

	RCU_INIT_POINTER(net->bpf.progs[type], NULL);

	netns_bpf_run_array_detach(net, type);

	net->bpf.progs[type] = NULL;

	bpf_prog_put(attached);

	return 0;

}
@@ -272,7 +310,7 @@ int netns_bpf_prog_detach(const union bpf_attr *attr) 
static int netns_bpf_link_attach(struct net *net, struct bpf_link *link,

				 enum netns_bpf_attach_type type)

{

	struct bpf_prog *prog;

	struct bpf_prog_array *run_array;

	int err;



	mutex_lock(&netns_bpf_mutex);
@@ -283,9 +321,7 @@ static int netns_bpf_link_attach(struct net *net, struct bpf_link *link, 
		goto out_unlock;

	}

	/* Links are not compatible with attaching prog directly */

	prog = rcu_dereference_protected(net->bpf.progs[type],

					 lockdep_is_held(&netns_bpf_mutex));

	if (prog) {

	if (net->bpf.progs[type]) {

		err = -EEXIST;

		goto out_unlock;

	}
@@ -301,7 +337,14 @@ static int netns_bpf_link_attach(struct net *net, struct bpf_link *link, 
	if (err)

		goto out_unlock;



	rcu_assign_pointer(net->bpf.progs[type], link->prog);

	run_array = bpf_prog_array_alloc(1, GFP_KERNEL);

	if (!run_array) {

		err = -ENOMEM;

		goto out_unlock;

	}

	run_array->items[0].prog = link->prog;

	rcu_assign_pointer(net->bpf.run_array[type], run_array);



	net->bpf.links[type] = link;



out_unlock:
@@ -368,11 +411,12 @@ static void __net_exit netns_bpf_pernet_pre_exit(struct net *net) 


	mutex_lock(&netns_bpf_mutex);

	for (type = 0; type < MAX_NETNS_BPF_ATTACH_TYPE; type++) {

		netns_bpf_run_array_detach(net, type);

		link = net->bpf.links[type];

		if (link)

			bpf_netns_link_auto_detach(link);

		else

			__netns_bpf_prog_detach(net, type);

		else if (net->bpf.progs[type])

			bpf_prog_put(net->bpf.progs[type]);

	}

	mutex_unlock(&netns_bpf_mutex);

}

net/core/flow_dissector.c

+10 −9
Original line number Diff line number Diff line
@@ -86,14 +86,14 @@ int flow_dissector_bpf_prog_attach_check(struct net *net, 
		for_each_net(ns) {

			if (ns == &init_net)

				continue;

			if (rcu_access_pointer(ns->bpf.progs[type]))

			if (rcu_access_pointer(ns->bpf.run_array[type]))

				return -EEXIST;

		}

	} else {

		/* Make sure root flow dissector is not attached

		 * when attaching to the non-root namespace.

		 */

		if (rcu_access_pointer(init_net.bpf.progs[type]))

		if (rcu_access_pointer(init_net.bpf.run_array[type]))

			return -EEXIST;

	}
@@ -894,7 +894,6 @@ bool __skb_flow_dissect(const struct net *net, 
	struct flow_dissector_key_addrs *key_addrs;

	struct flow_dissector_key_tags *key_tags;

	struct flow_dissector_key_vlan *key_vlan;

	struct bpf_prog *attached = NULL;

	enum flow_dissect_ret fdret;

	enum flow_dissector_key_id dissector_vlan = FLOW_DISSECTOR_KEY_MAX;

	bool mpls_el = false;
@@ -951,14 +950,14 @@ bool __skb_flow_dissect(const struct net *net, 
	WARN_ON_ONCE(!net);

	if (net) {

		enum netns_bpf_attach_type type = NETNS_BPF_FLOW_DISSECTOR;

		struct bpf_prog_array *run_array;



		rcu_read_lock();

		attached = rcu_dereference(init_net.bpf.progs[type]);

		run_array = rcu_dereference(init_net.bpf.run_array[type]);

		if (!run_array)

			run_array = rcu_dereference(net->bpf.run_array[type]);



		if (!attached)

			attached = rcu_dereference(net->bpf.progs[type]);



		if (attached) {

		if (run_array) {

			struct bpf_flow_keys flow_keys;

			struct bpf_flow_dissector ctx = {

				.flow_keys = &flow_keys,
@@ -966,6 +965,7 @@ bool __skb_flow_dissect(const struct net *net, 
				.data_end = data + hlen,

			};

			__be16 n_proto = proto;

			struct bpf_prog *prog;



			if (skb) {

				ctx.skb = skb;
@@ -976,7 +976,8 @@ bool __skb_flow_dissect(const struct net *net, 
				n_proto = skb->protocol;

			}



			ret = bpf_flow_dissect(attached, &ctx, n_proto, nhoff,

			prog = READ_ONCE(run_array->items[0].prog);

			ret = bpf_flow_dissect(prog, &ctx, n_proto, nhoff,

					       hlen, flags);

			__skb_flow_bpf_to_target(&flow_keys, flow_dissector,

						 target_container);

CRA Git | Maintained and supported by SUSTech CRA and CCSE