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: Joe Stringer <joe@wand.net.nz>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index e2070d819e0408442e46bfcb7622a10b83a8e5b4..f9187b41dff62cf81c03606fe9eba6f9f19d7a1e 100644 (file)
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -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.

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index cd0d8bc00bd1490b855a41d6d5d06bc21a7f48df..73c81bef6ae83c3e6c1393f01a998af0f399b318 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -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' */

diff --git a/net/core/filter.c b/net/core/filter.c
index b2cb186252e49160d6113267ec1029fc1a9092b2..591c698bc5178cd2466cd6a0f5c189c2e5600e43 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -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);
        }

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index e2070d819e0408442e46bfcb7622a10b83a8e5b4..f9187b41dff62cf81c03606fe9eba6f9f19d7a1e 100644 (file)
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -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.

diff --git a/tools/testing/selftests/bpf/bpf_helpers.h b/tools/testing/selftests/bpf/bpf_helpers.h
index e4be7730222dff86afb2f6a7fbeb24ddc027ba7e..1d407b3494f949520c8c4cb8d0303c1d70dfba27 100644 (file)
--- a/tools/testing/selftests/bpf/bpf_helpers.h
+++ b/tools/testing/selftests/bpf/bpf_helpers.h
@@ -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