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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 <joe@wand.net.nz>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Joe Stringer 2018-10-02 13:35:36 -07:00 • committed by Daniel Borkmann
parent fd978bf7fd
commit 6acc9b432e
5 changed files with 354 additions and 3 deletions
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93
tools/include/uapi/linux/bpf.h
View file

@ -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.