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// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "ipc/ipc_channel.h"
#include <sys/socket.h> // for CMSG macros
#include <queue>
#include <set>
#include <string>
#include <vector>
#include "base/files/scoped_file.h"
#include "base/message_loop/message_loop.h"
#include "base/process/process.h"
#include "ipc/ipc_channel_reader.h"
#include "ipc/ipc_message_attachment_set.h"
#if !defined(OS_MACOSX)
// On Linux, the seccomp sandbox makes it very expensive to call
// recvmsg() and sendmsg(). The restriction on calling read() and write(), which
// are cheap, is that we can't pass file descriptors over them.
// As we cannot anticipate when the sender will provide us with file
// descriptors, we have to make the decision about whether we call read() or
// recvmsg() before we actually make the call. The easiest option is to
// create a dedicated socketpair() for exchanging file descriptors. Any file
// descriptors are split out of a message, with the non-file-descriptor payload
// going over the normal connection, and the file descriptors being sent
// separately over the other channel. When read()ing from a channel, we'll
// notice if the message was supposed to have come with file descriptors and
// use recvmsg on the other socketpair to retrieve them and combine them
// back with the rest of the message.
// Mac can also run in IPC_USES_READWRITE mode if necessary, but at this time
// doesn't take a performance hit from recvmsg and sendmsg, so it doesn't
// make sense to waste resources on having the separate dedicated socketpair.
// It is however useful for debugging between Linux and Mac to be able to turn
// this switch 'on' on the Mac as well.
// The HELLO message from the client to the server is always sent using
// sendmsg because it will contain the file descriptor that the server
// needs to send file descriptors in later messages.
namespace IPC {
class IPC_EXPORT ChannelPosix : public Channel,
public internal::ChannelReader,
public base::MessageLoopForIO::Watcher {
ChannelPosix(const IPC::ChannelHandle& channel_handle, Mode mode,
Listener* listener);
~ChannelPosix() override;
// Channel implementation
bool Connect() override;
void Close() override;
bool Send(Message* message) override;
base::ProcessId GetPeerPID() const override;
base::ProcessId GetSelfPID() const override;
int GetClientFileDescriptor() const override;
base::ScopedFD TakeClientFileDescriptor() override;
// Returns true if the channel supports listening for connections.
bool AcceptsConnections() const;
// Returns true if the channel supports listening for connections and is
// currently connected.
bool HasAcceptedConnection() const;
// Closes any currently connected socket, and returns to a listening state
// for more connections.
void ResetToAcceptingConnectionState();
// Returns true if the peer process' effective user id can be determined, in
// which case the supplied peer_euid is updated with it.
bool GetPeerEuid(uid_t* peer_euid) const;
void CloseClientFileDescriptor();
static bool IsNamedServerInitialized(const std::string& channel_id);
#if defined(OS_LINUX)
static void SetGlobalPid(int pid);
#endif // OS_LINUX
bool CreatePipe(const IPC::ChannelHandle& channel_handle);
bool ProcessOutgoingMessages();
bool AcceptConnection();
void ClosePipeOnError();
int GetHelloMessageProcId() const;
void QueueHelloMessage();
void CloseFileDescriptors(Message* msg);
void QueueCloseFDMessage(int fd, int hops);
// ChannelReader implementation.
ReadState ReadData(char* buffer, int buffer_len, int* bytes_read) override;
bool WillDispatchInputMessage(Message* msg) override;
bool DidEmptyInputBuffers() override;
void HandleInternalMessage(const Message& msg) override;
// Reads the next message from the fd_pipe_ and appends them to the
// input_fds_ queue. Returns false if there was a message receiving error.
// True means there was a message and it was processed properly, or there was
// no messages.
bool ReadFileDescriptorsFromFDPipe();
// Finds the set of file descriptors in the given message. On success,
// appends the descriptors to the input_fds_ member and returns true
// Returns false if the message was truncated. In this case, any handles that
// were sent will be closed.
bool ExtractFileDescriptorsFromMsghdr(msghdr* msg);
// Closes all handles in the input_fds_ list and clears the list. This is
// used to clean up handles in error conditions to avoid leaking the handles.
void ClearInputFDs();
// MessageLoopForIO::Watcher implementation.
void OnFileCanReadWithoutBlocking(int fd) override;
void OnFileCanWriteWithoutBlocking(int fd) override;
Mode mode_;
base::ProcessId peer_pid_;
// After accepting one client connection on our server socket we want to
// stop listening.
base::MessageLoopForIO::FileDescriptorWatcher read_watcher_;
base::MessageLoopForIO::FileDescriptorWatcher write_watcher_;
// Indicates whether we're currently blocked waiting for a write to complete.
bool is_blocked_on_write_;
bool waiting_connect_;
// If sending a message blocks then we use this variable
// to keep track of where we are.
size_t message_send_bytes_written_;
// File descriptor we're listening on for new connections if we listen
// for connections.
base::ScopedFD server_listen_pipe_;
// The pipe used for communication.
base::ScopedFD pipe_;
// For a server, the client end of our socketpair() -- the other end of our
// pipe_ that is passed to the client.
base::ScopedFD client_pipe_;
mutable base::Lock client_pipe_lock_; // Lock that protects |client_pipe_|.
// Linux/BSD use a dedicated socketpair() for passing file descriptors.
base::ScopedFD fd_pipe_;
base::ScopedFD remote_fd_pipe_;
// The "name" of our pipe. On Windows this is the global identifier for
// the pipe. On POSIX it's used as a key in a local map of file descriptors.
std::string pipe_name_;
// Messages to be sent are queued here.
std::queue<Message*> output_queue_;
// We assume a worst case: kReadBufferSize bytes of messages, where each
// message has no payload and a full complement of descriptors.
static const size_t kMaxReadFDs =
(Channel::kReadBufferSize / sizeof(IPC::Message::Header)) *
// Buffer size for file descriptors used for recvmsg. On Mac the CMSG macros
// don't seem to be constant so we have to pick a "large enough" value.
#if defined(OS_MACOSX)
static const size_t kMaxReadFDBuffer = 1024;
static const size_t kMaxReadFDBuffer = CMSG_SPACE(sizeof(int) * kMaxReadFDs);
// Temporary buffer used to receive the file descriptors from recvmsg.
// Code that writes into this should immediately read them out and save
// them to input_fds_, since this buffer will be re-used anytime we call
// recvmsg.
char input_cmsg_buf_[kMaxReadFDBuffer];
// File descriptors extracted from messages coming off of the channel. The
// handles may span messages and come off different channels from the message
// data (in the case of READWRITE), and are processed in FIFO here.
// NOTE: The implementation assumes underlying storage here is contiguous, so
// don't change to something like std::deque<> without changing the
// implementation!
std::vector<int> input_fds_;
void ResetSafely(base::ScopedFD* fd);
bool in_dtor_;
#if defined(OS_MACOSX)
// On OSX, sent FDs must not be closed until we get an ack.
// Keep track of sent FDs here to make sure the remote is not
// trying to bamboozle us.
std::set<int> fds_to_close_;
// True if we are responsible for unlinking the unix domain socket file.
bool must_unlink_;
#if defined(OS_LINUX)
// If non-zero, overrides the process ID sent in the hello message.
static int global_pid_;
#endif // OS_LINUX
} // namespace IPC