sandboxed-api/sandboxed_api/sandbox2/comms.h

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// Copyright 2019 Google LLC. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// The sandbox2::Comms class uses AF_UNIX sockets in the abstract namespace
// (man 7 unix) to send pieces of data between processes. It uses the TLV
// encoding and provides some useful helpers.
//
// The endianess is platform-specific, but as it can be used over abstract
// sockets only, that's not a problem. Is some poor soul decides to rewrite it
// to work over AF_INET(6), the endianess will have to be dealt with (somehow).
#ifndef SANDBOXED_API_SANDBOX2_COMMS_H_
#define SANDBOXED_API_SANDBOX2_COMMS_H_
#include <sys/un.h>
#include <unistd.h>
#include <cstdint>
#include <limits>
#include <memory>
#include <string>
#include "absl/base/attributes.h"
#include "absl/synchronization/mutex.h"
#include "sandboxed_api/util/status.h"
#include "sandboxed_api/util/status.pb.h"
namespace proto2 {
class Message;
}
namespace sandbox2 {
class Comms {
public:
// Default tags, custom tags should be <0x80000000.
static constexpr uint32_t kTagBool = 0x80000001;
static constexpr uint32_t kTagInt8 = 0x80000002;
static constexpr uint32_t kTagUint8 = 0x80000003;
static constexpr uint32_t kTagInt16 = 0x80000004;
static constexpr uint32_t kTagUint16 = 0x80000005;
static constexpr uint32_t kTagInt32 = 0x80000006;
static constexpr uint32_t kTagUint32 = 0x80000007;
static constexpr uint32_t kTagInt64 = 0x80000008;
static constexpr uint32_t kTagUint64 = 0x80000009;
static constexpr uint32_t kTagString = 0x80000100;
static constexpr uint32_t kTagBytes = 0x80000101;
static constexpr uint32_t kTagProto2 = 0x80000102;
static constexpr uint32_t kTagFd = 0X80000201;
// Any payload size above this limit will LOG(WARNING).
static constexpr uint64_t kWarnMsgSize = (256ULL << 20);
// Sandbox2-specific convention where FD=1023 is always passed to the
// sandboxed process as a communication channel (encapsulated in the
// sandbox2::Comms object at the server-side).
static constexpr int kSandbox2ClientCommsFD = 1023;
// This object will have to be connected later on.
explicit Comms(const std::string& socket_name);
Comms(const Comms&) = delete;
Comms& operator=(const Comms&) = delete;
// Instantiates a pre-connected object.
// Takes ownership over fd, which will be closed on object's destruction.
explicit Comms(int fd);
~Comms();
// Binds to an address and make it listen to connections.
bool Listen();
// Accepts the connection.
bool Accept();
// Connects to a remote socket.
bool Connect();
// Terminates all underlying file descriptors, and sets the status of the
// Comms object to TERMINATED.
void Terminate();
// Returns the already connected FD.
int GetConnectionFD() const;
bool IsConnected() const { return state_ == State::kConnected; }
bool IsTerminated() const { return state_ == State::kTerminated; }
// Returns the maximum size of a message that can be send over the comms
// channel.
// Note: The actual size is "unlimited", although the Buffer API is more
// efficient for large transfers. There is an arbitrary limit to ~2GiB to
// avoid protobuf serialization issues.
uint64_t GetMaxMsgSize() const { return std::numeric_limits<int32_t>::max(); }
bool SendTLV(uint32_t tag, uint64_t length, const uint8_t* bytes);
// Receive a TLV structure, the memory for the value will be allocated
// by std::vector.
bool RecvTLV(uint32_t* tag, std::vector<uint8_t>* value);
// Receives a TLV value into a specified buffer without allocating memory.
bool RecvTLV(uint32_t* tag, uint64_t* length, void* buffer, uint64_t buffer_size);
// Sends/receives various types of data.
bool RecvUint8(uint8_t* v) { return RecvIntGeneric(v, kTagUint8); }
bool SendUint8(uint8_t v) { return SendGeneric(v, kTagUint8); }
bool RecvInt8(int8_t* v) { return RecvIntGeneric(v, kTagInt8); }
bool SendInt8(int8_t v) { return SendGeneric(v, kTagInt8); }
bool RecvUint16(uint16_t* v) { return RecvIntGeneric(v, kTagUint16); }
bool SendUint16(uint16_t v) { return SendGeneric(v, kTagUint16); }
bool RecvInt16(int16_t* v) { return RecvIntGeneric(v, kTagInt16); }
bool SendInt16(int16_t v) { return SendGeneric(v, kTagInt16); }
bool RecvUint32(uint32_t* v) { return RecvIntGeneric(v, kTagUint32); }
bool SendUint32(uint32_t v) { return SendGeneric(v, kTagUint32); }
bool RecvInt32(int32_t* v) { return RecvIntGeneric(v, kTagInt32); }
bool SendInt32(int32_t v) { return SendGeneric(v, kTagInt32); }
bool RecvUint64(uint64_t* v) { return RecvIntGeneric(v, kTagUint64); }
bool SendUint64(uint64_t v) { return SendGeneric(v, kTagUint64); }
bool RecvInt64(int64_t* v) { return RecvIntGeneric(v, kTagInt64); }
bool SendInt64(int64_t v) { return SendGeneric(v, kTagInt64); }
bool RecvBool(bool* v) { return RecvIntGeneric(v, kTagBool); }
bool SendBool(bool v) { return SendGeneric(v, kTagBool); }
bool RecvString(std::string* v);
bool SendString(const std::string& v);
bool RecvBytes(std::vector<uint8_t>* buffer);
bool SendBytes(const uint8_t* v, uint64_t len);
bool SendBytes(const std::vector<uint8_t>& buffer);
// Receives remote process credentials.
bool RecvCreds(pid_t* pid, uid_t* uid, gid_t* gid);
// Receives/sends file descriptors.
bool RecvFD(int* fd);
bool SendFD(int fd);
// Receives/sends protobufs.
bool RecvProtoBuf(google::protobuf::Message* message);
bool SendProtoBuf(const google::protobuf::Message& message);
// Receives/sends Status objects.
template <typename StatusT>
bool RecvStatus(StatusT* status);
template <typename StatusT>
bool SendStatus(const StatusT& status);
private:
// State of the channel
enum class State {
kUnconnected = 0,
kConnected,
kTerminated,
};
// Connection parameters.
std::string socket_name_;
int connection_fd_ = -1;
int bind_fd_ = -1;
// Mutex making sure that we serialize TLV messages (which consist out of
// three different calls to send / receive).
absl::Mutex tlv_send_transmission_mutex_;
absl::Mutex tlv_recv_transmission_mutex_;
// State of the channel (enum), socket will have to be connected later on.
State state_ = State::kUnconnected;
// TLV structure used to pass messages around.
struct TLV {
uint32_t tag;
std::vector<uint8_t> value;
};
// Special struct for passing credentials or FDs. Different from the one above
// as it inlines the value. This is important as the data is transmitted using
// sendmsg/recvmsg instead of send/recv.
struct ABSL_ATTRIBUTE_PACKED InternalTLV {
uint32_t tag;
uint32_t len;
uint64_t val;
};
// Fills sockaddr_un struct with proper values.
socklen_t CreateSockaddrUn(sockaddr_un* sun);
// Support for EINTR and size completion.
bool Send(const uint8_t* bytes, uint64_t len);
bool Recv(uint8_t* bytes, uint64_t len);
// Receives tag and length. Assumes that the `tlv_transmission_mutex_` mutex
// is locked.
bool RecvTL(uint32_t* tag, uint64_t* length)
EXCLUSIVE_LOCKS_REQUIRED(tlv_recv_transmission_mutex_);
// Receives whole TLV structure, allocates memory for the data.
bool RecvTLV(TLV* tlv);
// Receives arbitrary integers.
bool RecvInt(void* buffer, uint64_t len, uint32_t tag);
template <typename T>
bool RecvIntGeneric(T* output, uint32_t tag) {
return RecvInt(output, sizeof(T), tag);
}
template <typename T>
bool SendGeneric(T value, uint32_t tag) {
return SendTLV(tag, sizeof(T), reinterpret_cast<const uint8_t*>(&value));
}
};
template <typename StatusT>
bool Comms::RecvStatus(StatusT* status) {
sapi::StatusProto proto;
if (!RecvProtoBuf(&proto)) {
return false;
}
*status = sapi::MakeStatusFromProto(proto);
return true;
}
template <typename StatusT>
bool Comms::SendStatus(const StatusT& status) {
sapi::StatusProto proto;
sapi::SaveStatusToProto(status, &proto);
return SendProtoBuf(proto);
}
} // namespace sandbox2
#endif // SANDBOXED_API_SANDBOX2_COMMS_H_