Commit 6acc9b43 authored by Joe Stringer's avatar Joe Stringer Committed by Daniel Borkmann
Browse files

bpf: Add helper to retrieve socket in BPF 



This patch adds new BPF helper functions, bpf_sk_lookup_tcp() and
bpf_sk_lookup_udp() which allows BPF programs to find out if there is a
socket listening on this host, and returns a socket pointer which the
BPF program can then access to determine, for instance, whether to
forward or drop traffic. bpf_sk_lookup_xxx() may take a reference on the
socket, so when a BPF program makes use of this function, it must
subsequently pass the returned pointer into the newly added sk_release()
to return the reference.

By way of example, the following pseudocode would filter inbound
connections at XDP if there is no corresponding service listening for
the traffic:

  struct bpf_sock_tuple tuple;
  struct bpf_sock_ops *sk;

  populate_tuple(ctx, &tuple); // Extract the 5tuple from the packet
  sk = bpf_sk_lookup_tcp(ctx, &tuple, sizeof tuple, netns, 0);
  if (!sk) {
    // Couldn't find a socket listening for this traffic. Drop.
    return TC_ACT_SHOT;
  }
  bpf_sk_release(sk, 0);
  return TC_ACT_OK;

Signed-off-by: default avatarJoe Stringer <joe@wand.net.nz>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent fd978bf7

include/uapi/linux/bpf.h

+92 −1
Original line number Diff line number Diff line
@@ -2144,6 +2144,77 @@ union bpf_attr { 
 *		request in the skb.

 *	Return

 *		0 on success, or a negative error in case of failure.

 *

 * struct bpf_sock *bpf_sk_lookup_tcp(void *ctx, struct bpf_sock_tuple *tuple, u32 tuple_size, u32 netns, u64 flags)

 *	Description

 *		Look for TCP socket matching *tuple*, optionally in a child

 *		network namespace *netns*. The return value must be checked,

 *		and if non-NULL, released via **bpf_sk_release**\ ().

 *

 *		The *ctx* should point to the context of the program, such as

 *		the skb or socket (depending on the hook in use). This is used

 *		to determine the base network namespace for the lookup.

 *

 *		*tuple_size* must be one of:

 *

 *		**sizeof**\ (*tuple*\ **->ipv4**)

 *			Look for an IPv4 socket.

 *		**sizeof**\ (*tuple*\ **->ipv6**)

 *			Look for an IPv6 socket.

 *

 *		If the *netns* is zero, then the socket lookup table in the

 *		netns associated with the *ctx* will be used. For the TC hooks,

 *		this in the netns of the device in the skb. For socket hooks,

 *		this in the netns of the socket. If *netns* is non-zero, then

 *		it specifies the ID of the netns relative to the netns

 *		associated with the *ctx*.

 *

 *		All values for *flags* are reserved for future usage, and must

 *		be left at zero.

 *

 *		This helper is available only if the kernel was compiled with

 *		**CONFIG_NET** configuration option.

 *	Return

 *		Pointer to *struct bpf_sock*, or NULL in case of failure.

 *

 * struct bpf_sock *bpf_sk_lookup_udp(void *ctx, struct bpf_sock_tuple *tuple, u32 tuple_size, u32 netns, u64 flags)

 *	Description

 *		Look for UDP socket matching *tuple*, optionally in a child

 *		network namespace *netns*. The return value must be checked,

 *		and if non-NULL, released via **bpf_sk_release**\ ().

 *

 *		The *ctx* should point to the context of the program, such as

 *		the skb or socket (depending on the hook in use). This is used

 *		to determine the base network namespace for the lookup.

 *

 *		*tuple_size* must be one of:

 *

 *		**sizeof**\ (*tuple*\ **->ipv4**)

 *			Look for an IPv4 socket.

 *		**sizeof**\ (*tuple*\ **->ipv6**)

 *			Look for an IPv6 socket.

 *

 *		If the *netns* is zero, then the socket lookup table in the

 *		netns associated with the *ctx* will be used. For the TC hooks,

 *		this in the netns of the device in the skb. For socket hooks,

 *		this in the netns of the socket. If *netns* is non-zero, then

 *		it specifies the ID of the netns relative to the netns

 *		associated with the *ctx*.

 *

 *		All values for *flags* are reserved for future usage, and must

 *		be left at zero.

 *

 *		This helper is available only if the kernel was compiled with

 *		**CONFIG_NET** configuration option.

 *	Return

 *		Pointer to *struct bpf_sock*, or NULL in case of failure.

 *

 * int bpf_sk_release(struct bpf_sock *sk)

 *	Description

 *		Release the reference held by *sock*. *sock* must be a non-NULL

 *		pointer that was returned from bpf_sk_lookup_xxx\ ().

 *	Return

 *		0 on success, or a negative error in case of failure.

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -2229,7 +2300,10 @@ union bpf_attr { 
	FN(get_current_cgroup_id),	\

	FN(get_local_storage),		\

	FN(sk_select_reuseport),	\

	FN(skb_ancestor_cgroup_id),

	FN(skb_ancestor_cgroup_id),	\

	FN(sk_lookup_tcp),		\

	FN(sk_lookup_udp),		\

	FN(sk_release),



/* integer value in 'imm' field of BPF_CALL instruction selects which helper

 * function eBPF program intends to call
@@ -2399,6 +2473,23 @@ struct bpf_sock { 
				 */

};



struct bpf_sock_tuple {

	union {

		struct {

			__be32 saddr;

			__be32 daddr;

			__be16 sport;

			__be16 dport;

		} ipv4;

		struct {

			__be32 saddr[4];

			__be32 daddr[4];

			__be16 sport;

			__be16 dport;

		} ipv6;

	};

};



#define XDP_PACKET_HEADROOM 256



/* User return codes for XDP prog type.

kernel/bpf/verifier.c

+7 −1
Original line number Diff line number Diff line
@@ -153,6 +153,12 @@ static const struct bpf_verifier_ops * const bpf_verifier_ops[] = { 
 * PTR_TO_MAP_VALUE, PTR_TO_SOCKET_OR_NULL becomes PTR_TO_SOCKET when the type

 * passes through a NULL-check conditional. For the branch wherein the state is

 * changed to CONST_IMM, the verifier releases the reference.

 *

 * For each helper function that allocates a reference, such as

 * bpf_sk_lookup_tcp(), there is a corresponding release function, such as

 * bpf_sk_release(). When a reference type passes into the release function,

 * the verifier also releases the reference. If any unchecked or unreleased

 * reference remains at the end of the program, the verifier rejects it.

 */



/* verifier_state + insn_idx are pushed to stack when branch is encountered */
@@ -300,7 +306,7 @@ static bool arg_type_is_refcounted(enum bpf_arg_type type) 
 */

static bool is_release_function(enum bpf_func_id func_id)

{

	return false;

	return func_id == BPF_FUNC_sk_release;

}



/* string representation of 'enum bpf_reg_type' */

net/core/filter.c

+151 −0
Original line number Diff line number Diff line
@@ -58,13 +58,17 @@ 
#include <net/busy_poll.h>

#include <net/tcp.h>

#include <net/xfrm.h>

#include <net/udp.h>

#include <linux/bpf_trace.h>

#include <net/xdp_sock.h>

#include <linux/inetdevice.h>

#include <net/inet_hashtables.h>

#include <net/inet6_hashtables.h>

#include <net/ip_fib.h>

#include <net/flow.h>

#include <net/arp.h>

#include <net/ipv6.h>

#include <net/net_namespace.h>

#include <linux/seg6_local.h>

#include <net/seg6.h>

#include <net/seg6_local.h>
@@ -4813,6 +4817,141 @@ static const struct bpf_func_proto bpf_lwt_seg6_adjust_srh_proto = { 
};

#endif /* CONFIG_IPV6_SEG6_BPF */



struct sock *sk_lookup(struct net *net, struct bpf_sock_tuple *tuple,

		       struct sk_buff *skb, u8 family, u8 proto)

{

	int dif = skb->dev->ifindex;

	bool refcounted = false;

	struct sock *sk = NULL;



	if (family == AF_INET) {

		__be32 src4 = tuple->ipv4.saddr;

		__be32 dst4 = tuple->ipv4.daddr;

		int sdif = inet_sdif(skb);



		if (proto == IPPROTO_TCP)

			sk = __inet_lookup(net, &tcp_hashinfo, skb, 0,

					   src4, tuple->ipv4.sport,

					   dst4, tuple->ipv4.dport,

					   dif, sdif, &refcounted);

		else

			sk = __udp4_lib_lookup(net, src4, tuple->ipv4.sport,

					       dst4, tuple->ipv4.dport,

					       dif, sdif, &udp_table, skb);

#if IS_ENABLED(CONFIG_IPV6)

	} else {

		struct in6_addr *src6 = (struct in6_addr *)&tuple->ipv6.saddr;

		struct in6_addr *dst6 = (struct in6_addr *)&tuple->ipv6.daddr;

		int sdif = inet6_sdif(skb);



		if (proto == IPPROTO_TCP)

			sk = __inet6_lookup(net, &tcp_hashinfo, skb, 0,

					    src6, tuple->ipv6.sport,

					    dst6, tuple->ipv6.dport,

					    dif, sdif, &refcounted);

		else

			sk = __udp6_lib_lookup(net, src6, tuple->ipv6.sport,

					       dst6, tuple->ipv6.dport,

					       dif, sdif, &udp_table, skb);

#endif

	}



	if (unlikely(sk && !refcounted && !sock_flag(sk, SOCK_RCU_FREE))) {

		WARN_ONCE(1, "Found non-RCU, unreferenced socket!");

		sk = NULL;

	}

	return sk;

}



/* bpf_sk_lookup performs the core lookup for different types of sockets,

 * taking a reference on the socket if it doesn't have the flag SOCK_RCU_FREE.

 * Returns the socket as an 'unsigned long' to simplify the casting in the

 * callers to satisfy BPF_CALL declarations.

 */

static unsigned long

bpf_sk_lookup(struct sk_buff *skb, struct bpf_sock_tuple *tuple, u32 len,

	      u8 proto, u64 netns_id, u64 flags)

{

	struct net *caller_net;

	struct sock *sk = NULL;

	u8 family = AF_UNSPEC;

	struct net *net;



	family = len == sizeof(tuple->ipv4) ? AF_INET : AF_INET6;

	if (unlikely(family == AF_UNSPEC || netns_id > U32_MAX || flags))

		goto out;



	if (skb->dev)

		caller_net = dev_net(skb->dev);

	else

		caller_net = sock_net(skb->sk);

	if (netns_id) {

		net = get_net_ns_by_id(caller_net, netns_id);

		if (unlikely(!net))

			goto out;

		sk = sk_lookup(net, tuple, skb, family, proto);

		put_net(net);

	} else {

		net = caller_net;

		sk = sk_lookup(net, tuple, skb, family, proto);

	}



	if (sk)

		sk = sk_to_full_sk(sk);

out:

	return (unsigned long) sk;

}



BPF_CALL_5(bpf_sk_lookup_tcp, struct sk_buff *, skb,

	   struct bpf_sock_tuple *, tuple, u32, len, u64, netns_id, u64, flags)

{

	return bpf_sk_lookup(skb, tuple, len, IPPROTO_TCP, netns_id, flags);

}



static const struct bpf_func_proto bpf_sk_lookup_tcp_proto = {

	.func		= bpf_sk_lookup_tcp,

	.gpl_only	= false,

	.pkt_access	= true,

	.ret_type	= RET_PTR_TO_SOCKET_OR_NULL,

	.arg1_type	= ARG_PTR_TO_CTX,

	.arg2_type	= ARG_PTR_TO_MEM,

	.arg3_type	= ARG_CONST_SIZE,

	.arg4_type	= ARG_ANYTHING,

	.arg5_type	= ARG_ANYTHING,

};



BPF_CALL_5(bpf_sk_lookup_udp, struct sk_buff *, skb,

	   struct bpf_sock_tuple *, tuple, u32, len, u64, netns_id, u64, flags)

{

	return bpf_sk_lookup(skb, tuple, len, IPPROTO_UDP, netns_id, flags);

}



static const struct bpf_func_proto bpf_sk_lookup_udp_proto = {

	.func		= bpf_sk_lookup_udp,

	.gpl_only	= false,

	.pkt_access	= true,

	.ret_type	= RET_PTR_TO_SOCKET_OR_NULL,

	.arg1_type	= ARG_PTR_TO_CTX,

	.arg2_type	= ARG_PTR_TO_MEM,

	.arg3_type	= ARG_CONST_SIZE,

	.arg4_type	= ARG_ANYTHING,

	.arg5_type	= ARG_ANYTHING,

};



BPF_CALL_1(bpf_sk_release, struct sock *, sk)

{

	if (!sock_flag(sk, SOCK_RCU_FREE))

		sock_gen_put(sk);

	return 0;

}



static const struct bpf_func_proto bpf_sk_release_proto = {

	.func		= bpf_sk_release,

	.gpl_only	= false,

	.ret_type	= RET_INTEGER,

	.arg1_type	= ARG_PTR_TO_SOCKET,

};



bool bpf_helper_changes_pkt_data(void *func)

{

	if (func == bpf_skb_vlan_push ||
@@ -5019,6 +5158,12 @@ tc_cls_act_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) 
	case BPF_FUNC_skb_ancestor_cgroup_id:

		return &bpf_skb_ancestor_cgroup_id_proto;

#endif

	case BPF_FUNC_sk_lookup_tcp:

		return &bpf_sk_lookup_tcp_proto;

	case BPF_FUNC_sk_lookup_udp:

		return &bpf_sk_lookup_udp_proto;

	case BPF_FUNC_sk_release:

		return &bpf_sk_release_proto;

	default:

		return bpf_base_func_proto(func_id);

	}
@@ -5119,6 +5264,12 @@ sk_skb_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) 
		return &bpf_sk_redirect_hash_proto;

	case BPF_FUNC_get_local_storage:

		return &bpf_get_local_storage_proto;

	case BPF_FUNC_sk_lookup_tcp:

		return &bpf_sk_lookup_tcp_proto;

	case BPF_FUNC_sk_lookup_udp:

		return &bpf_sk_lookup_udp_proto;

	case BPF_FUNC_sk_release:

		return &bpf_sk_release_proto;

	default:

		return bpf_base_func_proto(func_id);

	}

tools/include/uapi/linux/bpf.h

+92 −1
Original line number Diff line number Diff line
@@ -2144,6 +2144,77 @@ union bpf_attr { 
 *		request in the skb.

 *	Return

 *		0 on success, or a negative error in case of failure.

 *

 * struct bpf_sock *bpf_sk_lookup_tcp(void *ctx, struct bpf_sock_tuple *tuple, u32 tuple_size, u32 netns, u64 flags)

 *	Description

 *		Look for TCP socket matching *tuple*, optionally in a child

 *		network namespace *netns*. The return value must be checked,

 *		and if non-NULL, released via **bpf_sk_release**\ ().

 *

 *		The *ctx* should point to the context of the program, such as

 *		the skb or socket (depending on the hook in use). This is used

 *		to determine the base network namespace for the lookup.

 *

 *		*tuple_size* must be one of:

 *

 *		**sizeof**\ (*tuple*\ **->ipv4**)

 *			Look for an IPv4 socket.

 *		**sizeof**\ (*tuple*\ **->ipv6**)

 *			Look for an IPv6 socket.

 *

 *		If the *netns* is zero, then the socket lookup table in the

 *		netns associated with the *ctx* will be used. For the TC hooks,

 *		this in the netns of the device in the skb. For socket hooks,

 *		this in the netns of the socket. If *netns* is non-zero, then

 *		it specifies the ID of the netns relative to the netns

 *		associated with the *ctx*.

 *

 *		All values for *flags* are reserved for future usage, and must

 *		be left at zero.

 *

 *		This helper is available only if the kernel was compiled with

 *		**CONFIG_NET** configuration option.

 *	Return

 *		Pointer to *struct bpf_sock*, or NULL in case of failure.

 *

 * struct bpf_sock *bpf_sk_lookup_udp(void *ctx, struct bpf_sock_tuple *tuple, u32 tuple_size, u32 netns, u64 flags)

 *	Description

 *		Look for UDP socket matching *tuple*, optionally in a child

 *		network namespace *netns*. The return value must be checked,

 *		and if non-NULL, released via **bpf_sk_release**\ ().

 *

 *		The *ctx* should point to the context of the program, such as

 *		the skb or socket (depending on the hook in use). This is used

 *		to determine the base network namespace for the lookup.

 *

 *		*tuple_size* must be one of:

 *

 *		**sizeof**\ (*tuple*\ **->ipv4**)

 *			Look for an IPv4 socket.

 *		**sizeof**\ (*tuple*\ **->ipv6**)

 *			Look for an IPv6 socket.

 *

 *		If the *netns* is zero, then the socket lookup table in the

 *		netns associated with the *ctx* will be used. For the TC hooks,

 *		this in the netns of the device in the skb. For socket hooks,

 *		this in the netns of the socket. If *netns* is non-zero, then

 *		it specifies the ID of the netns relative to the netns

 *		associated with the *ctx*.

 *

 *		All values for *flags* are reserved for future usage, and must

 *		be left at zero.

 *

 *		This helper is available only if the kernel was compiled with

 *		**CONFIG_NET** configuration option.

 *	Return

 *		Pointer to *struct bpf_sock*, or NULL in case of failure.

 *

 * int bpf_sk_release(struct bpf_sock *sk)

 *	Description

 *		Release the reference held by *sock*. *sock* must be a non-NULL

 *		pointer that was returned from bpf_sk_lookup_xxx\ ().

 *	Return

 *		0 on success, or a negative error in case of failure.

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -2229,7 +2300,10 @@ union bpf_attr { 
	FN(get_current_cgroup_id),	\

	FN(get_local_storage),		\

	FN(sk_select_reuseport),	\

	FN(skb_ancestor_cgroup_id),

	FN(skb_ancestor_cgroup_id),	\

	FN(sk_lookup_tcp),		\

	FN(sk_lookup_udp),		\

	FN(sk_release),



/* integer value in 'imm' field of BPF_CALL instruction selects which helper

 * function eBPF program intends to call
@@ -2399,6 +2473,23 @@ struct bpf_sock { 
				 */

};



struct bpf_sock_tuple {

	union {

		struct {

			__be32 saddr;

			__be32 daddr;

			__be16 sport;

			__be16 dport;

		} ipv4;

		struct {

			__be32 saddr[4];

			__be32 daddr[4];

			__be16 sport;

			__be16 dport;

		} ipv6;

	};

};



#define XDP_PACKET_HEADROOM 256



/* User return codes for XDP prog type.

tools/testing/selftests/bpf/bpf_helpers.h

+12 −0
Original line number Diff line number Diff line
@@ -143,6 +143,18 @@ static unsigned long long (*bpf_skb_cgroup_id)(void *ctx) = 
	(void *) BPF_FUNC_skb_cgroup_id;

static unsigned long long (*bpf_skb_ancestor_cgroup_id)(void *ctx, int level) =

	(void *) BPF_FUNC_skb_ancestor_cgroup_id;

static struct bpf_sock *(*bpf_sk_lookup_tcp)(void *ctx,

					     struct bpf_sock_tuple *tuple,

					     int size, unsigned int netns_id,

					     unsigned long long flags) =

	(void *) BPF_FUNC_sk_lookup_tcp;

static struct bpf_sock *(*bpf_sk_lookup_udp)(void *ctx,

					     struct bpf_sock_tuple *tuple,

					     int size, unsigned int netns_id,

					     unsigned long long flags) =

	(void *) BPF_FUNC_sk_lookup_udp;

static int (*bpf_sk_release)(struct bpf_sock *sk) =

	(void *) BPF_FUNC_sk_release;



/* llvm builtin functions that eBPF C program may use to

 * emit BPF_LD_ABS and BPF_LD_IND instructions

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