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bpf: Add helper to retrieve socket in BPF
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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: Joe Stringer <[email protected]>
Acked-by: Alexei Starovoitov <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
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@joestringer @borkmann
joestringer authored and borkmann committed Oct 3, 2018
1 parent fd978bf commit 6acc9b4
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Showing 5 changed files with 354 additions and 3 deletions.
93 changes: 92 additions & 1 deletion include/uapi/linux/bpf.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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), \
Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -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.
Expand Down
8 changes: 7 additions & 1 deletion kernel/bpf/verifier.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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 */
Expand Down Expand Up @@ -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' */
Expand Down
151 changes: 151 additions & 0 deletions net/core/filter.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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>
Expand Down Expand Up @@ -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 ||
Expand Down Expand Up @@ -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);
}
Expand Down Expand Up @@ -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);
}
Expand Down
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