/* * Copyright (C) 2015 The Android Open Source Project * * 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. */ // Functionality for launching and managing shell subprocesses. // // There are two types of subprocesses, PTY or raw. PTY is typically used for // an interactive session, raw for non-interactive. There are also two methods // of communication with the subprocess, passing raw data or using a simple // protocol to wrap packets. The protocol allows separating stdout/stderr and // passing the exit code back, but is not backwards compatible. // ----------------+-------------------------------------- // Type Protocol | Exit code? Separate stdout/stderr? // ----------------+-------------------------------------- // PTY No | No No // Raw No | No No // PTY Yes | Yes No // Raw Yes | Yes Yes // ----------------+-------------------------------------- // // Non-protocol subprocesses work by passing subprocess stdin/out/err through // a single pipe which is registered with a local socket in adbd. The local // socket uses the fdevent loop to pass raw data between this pipe and the // transport, which then passes data back to the adb client. Cleanup is done by // waiting in a separate thread for the subprocesses to exit and then signaling // a separate fdevent to close out the local socket from the main loop. // // ------------------+-------------------------+------------------------------ // Subprocess | adbd subprocess thread | adbd main fdevent loop // ------------------+-------------------------+------------------------------ // | | // stdin/out/err <-----------------------------> LocalSocket // | | | // | | Block on exit | // | | * | // v | * | // Exit ---> Unblock | // | | | // | v | // | Notify shell exit FD ---> Close LocalSocket // ------------------+-------------------------+------------------------------ // // The protocol requires the thread to intercept stdin/out/err in order to // wrap/unwrap data with shell protocol packets. // // ------------------+-------------------------+------------------------------ // Subprocess | adbd subprocess thread | adbd main fdevent loop // ------------------+-------------------------+------------------------------ // | | // stdin/out <---> Protocol <---> LocalSocket // stderr ---> Protocol ---> LocalSocket // | | | // v | | // Exit ---> Exit code protocol ---> LocalSocket // | | | // | v | // | Notify shell exit FD ---> Close LocalSocket // ------------------+-------------------------+------------------------------ // // An alternate approach is to put the protocol wrapping/unwrapping in the main // fdevent loop, which has the advantage of being able to re-use the existing // select() code for handling data streams. However, implementation turned out // to be more complex due to partial reads and non-blocking I/O so this model // was chosen instead. #define TRACE_TAG SHELL #include "sysdeps.h" #include "shell_service.h" #include <errno.h> #include <pty.h> #include <pwd.h> #include <sys/select.h> #include <termios.h> #include <memory> #include <string> #include <unordered_map> #include <vector> #include <android-base/logging.h> #include <android-base/stringprintf.h> #include <paths.h> #include <log/log.h> #include "adb.h" #include "adb_io.h" #include "adb_trace.h" #include "adb_utils.h" #include "security_log_tags.h" namespace { void init_subproc_child() { setsid(); // Set OOM score adjustment to prevent killing int fd = adb_open("/proc/self/oom_score_adj", O_WRONLY | O_CLOEXEC); if (fd >= 0) { adb_write(fd, "0", 1); adb_close(fd); } else { D("adb: unable to update oom_score_adj"); } } // Reads from |fd| until close or failure. std::string ReadAll(int fd) { char buffer[512]; std::string received; while (1) { int bytes = adb_read(fd, buffer, sizeof(buffer)); if (bytes <= 0) { break; } received.append(buffer, bytes); } return received; } // Helper to automatically close an FD when it goes out of scope. class ScopedFd { public: ScopedFd() {} ~ScopedFd() { Reset(); } void Reset(int fd=-1) { if (fd != fd_) { if (valid()) { adb_close(fd_); } fd_ = fd; } } int Release() { int temp = fd_; fd_ = -1; return temp; } bool valid() const { return fd_ >= 0; } int fd() const { return fd_; } private: int fd_ = -1; DISALLOW_COPY_AND_ASSIGN(ScopedFd); }; // Creates a socketpair and saves the endpoints to |fd1| and |fd2|. bool CreateSocketpair(ScopedFd* fd1, ScopedFd* fd2) { int sockets[2]; if (adb_socketpair(sockets) < 0) { PLOG(ERROR) << "cannot create socket pair"; return false; } fd1->Reset(sockets[0]); fd2->Reset(sockets[1]); return true; } class Subprocess { public: Subprocess(const std::string& command, const char* terminal_type, SubprocessType type, SubprocessProtocol protocol); ~Subprocess(); const std::string& command() const { return command_; } int local_socket_fd() const { return local_socket_sfd_.fd(); } pid_t pid() const { return pid_; } // Sets up FDs, forks a subprocess, starts the subprocess manager thread, // and exec's the child. Returns false on failure. bool ForkAndExec(std::string* _Nonnull error); private: // Opens the file at |pts_name|. int OpenPtyChildFd(const char* pts_name, ScopedFd* error_sfd); static void ThreadHandler(void* userdata); void PassDataStreams(); void WaitForExit(); ScopedFd* SelectLoop(fd_set* master_read_set_ptr, fd_set* master_write_set_ptr); // Input/output stream handlers. Success returns nullptr, failure returns // a pointer to the failed FD. ScopedFd* PassInput(); ScopedFd* PassOutput(ScopedFd* sfd, ShellProtocol::Id id); const std::string command_; const std::string terminal_type_; bool make_pty_raw_ = false; SubprocessType type_; SubprocessProtocol protocol_; pid_t pid_ = -1; ScopedFd local_socket_sfd_; // Shell protocol variables. ScopedFd stdinout_sfd_, stderr_sfd_, protocol_sfd_; std::unique_ptr<ShellProtocol> input_, output_; size_t input_bytes_left_ = 0; DISALLOW_COPY_AND_ASSIGN(Subprocess); }; Subprocess::Subprocess(const std::string& command, const char* terminal_type, SubprocessType type, SubprocessProtocol protocol) : command_(command), terminal_type_(terminal_type ? terminal_type : ""), type_(type), protocol_(protocol) { // If we aren't using the shell protocol we must allocate a PTY to properly close the // subprocess. PTYs automatically send SIGHUP to the slave-side process when the master side // of the PTY closes, which we rely on. If we use a raw pipe, processes that don't read/write, // e.g. screenrecord, will never notice the broken pipe and terminate. // The shell protocol doesn't require a PTY because it's always monitoring the local socket FD // with select() and will send SIGHUP manually to the child process. if (protocol_ == SubprocessProtocol::kNone && type_ == SubprocessType::kRaw) { // Disable PTY input/output processing since the client is expecting raw data. D("Can't create raw subprocess without shell protocol, using PTY in raw mode instead"); type_ = SubprocessType::kPty; make_pty_raw_ = true; } } Subprocess::~Subprocess() { WaitForExit(); } bool Subprocess::ForkAndExec(std::string* error) { ScopedFd child_stdinout_sfd, child_stderr_sfd; ScopedFd parent_error_sfd, child_error_sfd; char pts_name[PATH_MAX]; if (command_.empty()) { __android_log_security_bswrite(SEC_TAG_ADB_SHELL_INTERACTIVE, ""); } else { __android_log_security_bswrite(SEC_TAG_ADB_SHELL_CMD, command_.c_str()); } // Create a socketpair for the fork() child to report any errors back to the parent. Since we // use threads, logging directly from the child might deadlock due to locks held in another // thread during the fork. if (!CreateSocketpair(&parent_error_sfd, &child_error_sfd)) { *error = android::base::StringPrintf( "failed to create pipe for subprocess error reporting: %s", strerror(errno)); return false; } // Construct the environment for the child before we fork. passwd* pw = getpwuid(getuid()); std::unordered_map<std::string, std::string> env; if (environ) { char** current = environ; while (char* env_cstr = *current++) { std::string env_string = env_cstr; char* delimiter = strchr(env_string.c_str(), '='); // Drop any values that don't contain '='. if (delimiter) { *delimiter++ = '\0'; env[env_string.c_str()] = delimiter; } } } if (pw != nullptr) { // TODO: $HOSTNAME? Normally bash automatically sets that, but mksh doesn't. env["HOME"] = pw->pw_dir; env["LOGNAME"] = pw->pw_name; env["USER"] = pw->pw_name; env["SHELL"] = pw->pw_shell; } if (!terminal_type_.empty()) { env["TERM"] = terminal_type_; } std::vector<std::string> joined_env; for (auto it : env) { const char* key = it.first.c_str(); const char* value = it.second.c_str(); joined_env.push_back(android::base::StringPrintf("%s=%s", key, value)); } std::vector<const char*> cenv; for (const std::string& str : joined_env) { cenv.push_back(str.c_str()); } cenv.push_back(nullptr); if (type_ == SubprocessType::kPty) { int fd; pid_ = forkpty(&fd, pts_name, nullptr, nullptr); stdinout_sfd_.Reset(fd); } else { if (!CreateSocketpair(&stdinout_sfd_, &child_stdinout_sfd)) { *error = android::base::StringPrintf("failed to create socketpair for stdin/out: %s", strerror(errno)); return false; } // Raw subprocess + shell protocol allows for splitting stderr. if (protocol_ == SubprocessProtocol::kShell && !CreateSocketpair(&stderr_sfd_, &child_stderr_sfd)) { *error = android::base::StringPrintf("failed to create socketpair for stderr: %s", strerror(errno)); return false; } pid_ = fork(); } if (pid_ == -1) { *error = android::base::StringPrintf("fork failed: %s", strerror(errno)); return false; } if (pid_ == 0) { // Subprocess child. init_subproc_child(); if (type_ == SubprocessType::kPty) { child_stdinout_sfd.Reset(OpenPtyChildFd(pts_name, &child_error_sfd)); } dup2(child_stdinout_sfd.fd(), STDIN_FILENO); dup2(child_stdinout_sfd.fd(), STDOUT_FILENO); dup2(child_stderr_sfd.valid() ? child_stderr_sfd.fd() : child_stdinout_sfd.fd(), STDERR_FILENO); // exec doesn't trigger destructors, close the FDs manually. stdinout_sfd_.Reset(); stderr_sfd_.Reset(); child_stdinout_sfd.Reset(); child_stderr_sfd.Reset(); parent_error_sfd.Reset(); close_on_exec(child_error_sfd.fd()); if (command_.empty()) { execle(_PATH_BSHELL, _PATH_BSHELL, "-", nullptr, cenv.data()); } else { execle(_PATH_BSHELL, _PATH_BSHELL, "-c", command_.c_str(), nullptr, cenv.data()); } WriteFdExactly(child_error_sfd.fd(), "exec '" _PATH_BSHELL "' failed: "); WriteFdExactly(child_error_sfd.fd(), strerror(errno)); child_error_sfd.Reset(); _Exit(1); } // Subprocess parent. D("subprocess parent: stdin/stdout FD = %d, stderr FD = %d", stdinout_sfd_.fd(), stderr_sfd_.fd()); // Wait to make sure the subprocess exec'd without error. child_error_sfd.Reset(); std::string error_message = ReadAll(parent_error_sfd.fd()); if (!error_message.empty()) { *error = error_message; return false; } D("subprocess parent: exec completed"); if (protocol_ == SubprocessProtocol::kNone) { // No protocol: all streams pass through the stdinout FD and hook // directly into the local socket for raw data transfer. local_socket_sfd_.Reset(stdinout_sfd_.Release()); } else { // Shell protocol: create another socketpair to intercept data. if (!CreateSocketpair(&protocol_sfd_, &local_socket_sfd_)) { *error = android::base::StringPrintf( "failed to create socketpair to intercept data: %s", strerror(errno)); kill(pid_, SIGKILL); return false; } D("protocol FD = %d", protocol_sfd_.fd()); input_.reset(new ShellProtocol(protocol_sfd_.fd())); output_.reset(new ShellProtocol(protocol_sfd_.fd())); if (!input_ || !output_) { *error = "failed to allocate shell protocol objects"; kill(pid_, SIGKILL); return false; } // Don't let reads/writes to the subprocess block our thread. This isn't // likely but could happen under unusual circumstances, such as if we // write a ton of data to stdin but the subprocess never reads it and // the pipe fills up. for (int fd : {stdinout_sfd_.fd(), stderr_sfd_.fd()}) { if (fd >= 0) { if (!set_file_block_mode(fd, false)) { *error = android::base::StringPrintf( "failed to set non-blocking mode for fd %d", fd); kill(pid_, SIGKILL); return false; } } } } if (!adb_thread_create(ThreadHandler, this)) { *error = android::base::StringPrintf("failed to create subprocess thread: %s", strerror(errno)); kill(pid_, SIGKILL); return false; } D("subprocess parent: completed"); return true; } int Subprocess::OpenPtyChildFd(const char* pts_name, ScopedFd* error_sfd) { int child_fd = adb_open(pts_name, O_RDWR | O_CLOEXEC); if (child_fd == -1) { // Don't use WriteFdFmt; since we're in the fork() child we don't want // to allocate any heap memory to avoid race conditions. const char* messages[] = {"child failed to open pseudo-term slave ", pts_name, ": ", strerror(errno)}; for (const char* message : messages) { WriteFdExactly(error_sfd->fd(), message); } exit(-1); } if (make_pty_raw_) { termios tattr; if (tcgetattr(child_fd, &tattr) == -1) { int saved_errno = errno; WriteFdExactly(error_sfd->fd(), "tcgetattr failed: "); WriteFdExactly(error_sfd->fd(), strerror(saved_errno)); exit(-1); } cfmakeraw(&tattr); if (tcsetattr(child_fd, TCSADRAIN, &tattr) == -1) { int saved_errno = errno; WriteFdExactly(error_sfd->fd(), "tcsetattr failed: "); WriteFdExactly(error_sfd->fd(), strerror(saved_errno)); exit(-1); } } return child_fd; } void Subprocess::ThreadHandler(void* userdata) { Subprocess* subprocess = reinterpret_cast<Subprocess*>(userdata); adb_thread_setname(android::base::StringPrintf( "shell srvc %d", subprocess->local_socket_fd())); subprocess->PassDataStreams(); D("deleting Subprocess for PID %d", subprocess->pid()); delete subprocess; } void Subprocess::PassDataStreams() { if (!protocol_sfd_.valid()) { return; } // Start by trying to read from the protocol FD, stdout, and stderr. fd_set master_read_set, master_write_set; FD_ZERO(&master_read_set); FD_ZERO(&master_write_set); for (ScopedFd* sfd : {&protocol_sfd_, &stdinout_sfd_, &stderr_sfd_}) { if (sfd->valid()) { FD_SET(sfd->fd(), &master_read_set); } } // Pass data until the protocol FD or both the subprocess pipes die, at // which point we can't pass any more data. while (protocol_sfd_.valid() && (stdinout_sfd_.valid() || stderr_sfd_.valid())) { ScopedFd* dead_sfd = SelectLoop(&master_read_set, &master_write_set); if (dead_sfd) { D("closing FD %d", dead_sfd->fd()); FD_CLR(dead_sfd->fd(), &master_read_set); FD_CLR(dead_sfd->fd(), &master_write_set); if (dead_sfd == &protocol_sfd_) { // Using SIGHUP is a decent general way to indicate that the // controlling process is going away. If specific signals are // needed (e.g. SIGINT), pass those through the shell protocol // and only fall back on this for unexpected closures. D("protocol FD died, sending SIGHUP to pid %d", pid_); kill(pid_, SIGHUP); } dead_sfd->Reset(); } } } namespace { inline bool ValidAndInSet(const ScopedFd& sfd, fd_set* set) { return sfd.valid() && FD_ISSET(sfd.fd(), set); } } // namespace ScopedFd* Subprocess::SelectLoop(fd_set* master_read_set_ptr, fd_set* master_write_set_ptr) { fd_set read_set, write_set; int select_n = std::max(std::max(protocol_sfd_.fd(), stdinout_sfd_.fd()), stderr_sfd_.fd()) + 1; ScopedFd* dead_sfd = nullptr; // Keep calling select() and passing data until an FD closes/errors. while (!dead_sfd) { memcpy(&read_set, master_read_set_ptr, sizeof(read_set)); memcpy(&write_set, master_write_set_ptr, sizeof(write_set)); if (select(select_n, &read_set, &write_set, nullptr, nullptr) < 0) { if (errno == EINTR) { continue; } else { PLOG(ERROR) << "select failed, closing subprocess pipes"; stdinout_sfd_.Reset(); stderr_sfd_.Reset(); return nullptr; } } // Read stdout, write to protocol FD. if (ValidAndInSet(stdinout_sfd_, &read_set)) { dead_sfd = PassOutput(&stdinout_sfd_, ShellProtocol::kIdStdout); } // Read stderr, write to protocol FD. if (!dead_sfd && ValidAndInSet(stderr_sfd_, &read_set)) { dead_sfd = PassOutput(&stderr_sfd_, ShellProtocol::kIdStderr); } // Read protocol FD, write to stdin. if (!dead_sfd && ValidAndInSet(protocol_sfd_, &read_set)) { dead_sfd = PassInput(); // If we didn't finish writing, block on stdin write. if (input_bytes_left_) { FD_CLR(protocol_sfd_.fd(), master_read_set_ptr); FD_SET(stdinout_sfd_.fd(), master_write_set_ptr); } } // Continue writing to stdin; only happens if a previous write blocked. if (!dead_sfd && ValidAndInSet(stdinout_sfd_, &write_set)) { dead_sfd = PassInput(); // If we finished writing, go back to blocking on protocol read. if (!input_bytes_left_) { FD_SET(protocol_sfd_.fd(), master_read_set_ptr); FD_CLR(stdinout_sfd_.fd(), master_write_set_ptr); } } } // while (!dead_sfd) return dead_sfd; } ScopedFd* Subprocess::PassInput() { // Only read a new packet if we've finished writing the last one. if (!input_bytes_left_) { if (!input_->Read()) { // Read() uses ReadFdExactly() which sets errno to 0 on EOF. if (errno != 0) { PLOG(ERROR) << "error reading protocol FD " << protocol_sfd_.fd(); } return &protocol_sfd_; } if (stdinout_sfd_.valid()) { switch (input_->id()) { case ShellProtocol::kIdWindowSizeChange: int rows, cols, x_pixels, y_pixels; if (sscanf(input_->data(), "%dx%d,%dx%d", &rows, &cols, &x_pixels, &y_pixels) == 4) { winsize ws; ws.ws_row = rows; ws.ws_col = cols; ws.ws_xpixel = x_pixels; ws.ws_ypixel = y_pixels; ioctl(stdinout_sfd_.fd(), TIOCSWINSZ, &ws); } break; case ShellProtocol::kIdStdin: input_bytes_left_ = input_->data_length(); break; case ShellProtocol::kIdCloseStdin: if (type_ == SubprocessType::kRaw) { if (adb_shutdown(stdinout_sfd_.fd(), SHUT_WR) == 0) { return nullptr; } PLOG(ERROR) << "failed to shutdown writes to FD " << stdinout_sfd_.fd(); return &stdinout_sfd_; } else { // PTYs can't close just input, so rather than close the // FD and risk losing subprocess output, leave it open. // This only happens if the client starts a PTY shell // non-interactively which is rare and unsupported. // If necessary, the client can manually close the shell // with `exit` or by killing the adb client process. D("can't close input for PTY FD %d", stdinout_sfd_.fd()); } break; } } } if (input_bytes_left_ > 0) { int index = input_->data_length() - input_bytes_left_; int bytes = adb_write(stdinout_sfd_.fd(), input_->data() + index, input_bytes_left_); if (bytes == 0 || (bytes < 0 && errno != EAGAIN)) { if (bytes < 0) { PLOG(ERROR) << "error reading stdin FD " << stdinout_sfd_.fd(); } // stdin is done, mark this packet as finished and we'll just start // dumping any further data received from the protocol FD. input_bytes_left_ = 0; return &stdinout_sfd_; } else if (bytes > 0) { input_bytes_left_ -= bytes; } } return nullptr; } ScopedFd* Subprocess::PassOutput(ScopedFd* sfd, ShellProtocol::Id id) { int bytes = adb_read(sfd->fd(), output_->data(), output_->data_capacity()); if (bytes == 0 || (bytes < 0 && errno != EAGAIN)) { // read() returns EIO if a PTY closes; don't report this as an error, // it just means the subprocess completed. if (bytes < 0 && !(type_ == SubprocessType::kPty && errno == EIO)) { PLOG(ERROR) << "error reading output FD " << sfd->fd(); } return sfd; } if (bytes > 0 && !output_->Write(id, bytes)) { if (errno != 0) { PLOG(ERROR) << "error reading protocol FD " << protocol_sfd_.fd(); } return &protocol_sfd_; } return nullptr; } void Subprocess::WaitForExit() { int exit_code = 1; D("waiting for pid %d", pid_); while (true) { int status; if (pid_ == waitpid(pid_, &status, 0)) { D("post waitpid (pid=%d) status=%04x", pid_, status); if (WIFSIGNALED(status)) { exit_code = 0x80 | WTERMSIG(status); D("subprocess killed by signal %d", WTERMSIG(status)); break; } else if (!WIFEXITED(status)) { D("subprocess didn't exit"); break; } else if (WEXITSTATUS(status) >= 0) { exit_code = WEXITSTATUS(status); D("subprocess exit code = %d", WEXITSTATUS(status)); break; } } } // If we have an open protocol FD send an exit packet. if (protocol_sfd_.valid()) { output_->data()[0] = exit_code; if (output_->Write(ShellProtocol::kIdExit, 1)) { D("wrote the exit code packet: %d", exit_code); } else { PLOG(ERROR) << "failed to write the exit code packet"; } protocol_sfd_.Reset(); } // Pass the local socket FD to the shell cleanup fdevent. if (SHELL_EXIT_NOTIFY_FD >= 0) { int fd = local_socket_sfd_.fd(); if (WriteFdExactly(SHELL_EXIT_NOTIFY_FD, &fd, sizeof(fd))) { D("passed fd %d to SHELL_EXIT_NOTIFY_FD (%d) for pid %d", fd, SHELL_EXIT_NOTIFY_FD, pid_); // The shell exit fdevent now owns the FD and will close it once // the last bit of data flushes through. local_socket_sfd_.Release(); } else { PLOG(ERROR) << "failed to write fd " << fd << " to SHELL_EXIT_NOTIFY_FD (" << SHELL_EXIT_NOTIFY_FD << ") for pid " << pid_; } } } } // namespace // Create a pipe containing the error. static int ReportError(SubprocessProtocol protocol, const std::string& message) { int pipefd[2]; if (pipe(pipefd) != 0) { LOG(ERROR) << "failed to create pipe to report error"; return -1; } std::string buf = android::base::StringPrintf("error: %s\n", message.c_str()); if (protocol == SubprocessProtocol::kShell) { ShellProtocol::Id id = ShellProtocol::kIdStderr; uint32_t length = buf.length(); WriteFdExactly(pipefd[1], &id, sizeof(id)); WriteFdExactly(pipefd[1], &length, sizeof(length)); } WriteFdExactly(pipefd[1], buf.data(), buf.length()); if (protocol == SubprocessProtocol::kShell) { ShellProtocol::Id id = ShellProtocol::kIdExit; uint32_t length = 1; char exit_code = 126; WriteFdExactly(pipefd[1], &id, sizeof(id)); WriteFdExactly(pipefd[1], &length, sizeof(length)); WriteFdExactly(pipefd[1], &exit_code, sizeof(exit_code)); } adb_close(pipefd[1]); return pipefd[0]; } int StartSubprocess(const char* name, const char* terminal_type, SubprocessType type, SubprocessProtocol protocol) { D("starting %s subprocess (protocol=%s, TERM=%s): '%s'", type == SubprocessType::kRaw ? "raw" : "PTY", protocol == SubprocessProtocol::kNone ? "none" : "shell", terminal_type, name); Subprocess* subprocess = new Subprocess(name, terminal_type, type, protocol); if (!subprocess) { LOG(ERROR) << "failed to allocate new subprocess"; return ReportError(protocol, "failed to allocate new subprocess"); } std::string error; if (!subprocess->ForkAndExec(&error)) { LOG(ERROR) << "failed to start subprocess: " << error; delete subprocess; return ReportError(protocol, error); } D("subprocess creation successful: local_socket_fd=%d, pid=%d", subprocess->local_socket_fd(), subprocess->pid()); return subprocess->local_socket_fd(); }