bpf: export bpf_sock for BPF_PROG_TYPE_SOCK_OPS prog type

And let it use bpf_sk_storage_{get,delete} helpers to access socket
storage. Kernel context (struct bpf_sock_ops_kern) already has sk
member, so I just expose it to the BPF hooks. I use
PTR_TO_SOCKET_OR_NULL and return NULL in !is_fullsock case.

I also export bpf_tcp_sock to make it possible to access tcp socket stats.

Cc: Martin Lau <kafai@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

include/uapi/linux/bpf.h

@@ -3299,6 +3299,7 @@ struct bpf_sock_ops {
 	__u32 sk_txhash;
 	__u64 bytes_received;
 	__u64 bytes_acked;
+	__bpf_md_ptr(struct bpf_sock *, sk);
 };
 
 /* Definitions for bpf_sock_ops_cb_flags */

net/core/filter.c

@@ -6147,6 +6147,14 @@ sock_ops_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_get_local_storage_proto;
 	case BPF_FUNC_perf_event_output:
 		return &bpf_sockopt_event_output_proto;
+	case BPF_FUNC_sk_storage_get:
+		return &bpf_sk_storage_get_proto;
+	case BPF_FUNC_sk_storage_delete:
+		return &bpf_sk_storage_delete_proto;
+#ifdef CONFIG_INET
+	case BPF_FUNC_tcp_sock:
+		return &bpf_tcp_sock_proto;
+#endif /* CONFIG_INET */
 	default:
 		return bpf_base_func_proto(func_id);
 	}
@@ -6882,6 +6890,11 @@ static bool sock_ops_is_valid_access(int off, int size,
 			if (size != sizeof(__u64))
 				return false;
 			break;
+		case offsetof(struct bpf_sock_ops, sk):
+			if (size != sizeof(__u64))
+				return false;
+			info->reg_type = PTR_TO_SOCKET_OR_NULL;
+			break;
 		default:
 			if (size != size_default)
 				return false;
@@ -8053,6 +8066,19 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
 		SOCK_OPS_GET_OR_SET_FIELD(sk_txhash, sk_txhash,
 					  struct sock, type);
 		break;
+	case offsetof(struct bpf_sock_ops, sk):
+		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(
+						struct bpf_sock_ops_kern,
+						is_fullsock),
+				      si->dst_reg, si->src_reg,
+				      offsetof(struct bpf_sock_ops_kern,
+					       is_fullsock));
+		*insn++ = BPF_JMP_IMM(BPF_JEQ, si->dst_reg, 0, 1);
+		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(
+						struct bpf_sock_ops_kern, sk),
+				      si->dst_reg, si->src_reg,
+				      offsetof(struct bpf_sock_ops_kern, sk));
+		break;
 	}
 	return insn - insn_buf;
 }