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      1 //
      2 // Copyright (C) 2012 The Android Open Source Project
      3 //
      4 // Licensed under the Apache License, Version 2.0 (the "License");
      5 // you may not use this file except in compliance with the License.
      6 // You may obtain a copy of the License at
      7 //
      8 //      http://www.apache.org/licenses/LICENSE-2.0
      9 //
     10 // Unless required by applicable law or agreed to in writing, software
     11 // distributed under the License is distributed on an "AS IS" BASIS,
     12 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13 // See the License for the specific language governing permissions and
     14 // limitations under the License.
     15 //
     16 
     17 #include "update_engine/common/subprocess.h"
     18 
     19 #include <fcntl.h>
     20 #include <stdlib.h>
     21 #include <string.h>
     22 #include <unistd.h>
     23 
     24 #include <memory>
     25 #include <string>
     26 #include <vector>
     27 
     28 #include <base/bind.h>
     29 #include <base/logging.h>
     30 #include <base/posix/eintr_wrapper.h>
     31 #include <base/strings/string_util.h>
     32 #include <base/strings/stringprintf.h>
     33 #include <brillo/process.h>
     34 #include <brillo/secure_blob.h>
     35 
     36 #include "update_engine/common/utils.h"
     37 
     38 using brillo::MessageLoop;
     39 using std::string;
     40 using std::unique_ptr;
     41 using std::vector;
     42 
     43 namespace chromeos_update_engine {
     44 
     45 namespace {
     46 
     47 bool SetupChild(const std::map<string, string>& env, uint32_t flags) {
     48   // Setup the environment variables.
     49   clearenv();
     50   for (const auto& key_value : env) {
     51     setenv(key_value.first.c_str(), key_value.second.c_str(), 0);
     52   }
     53 
     54   if ((flags & Subprocess::kRedirectStderrToStdout) != 0) {
     55     if (HANDLE_EINTR(dup2(STDOUT_FILENO, STDERR_FILENO)) != STDERR_FILENO)
     56       return false;
     57   }
     58 
     59   int fd = HANDLE_EINTR(open("/dev/null", O_RDONLY));
     60   if (fd < 0)
     61     return false;
     62   if (HANDLE_EINTR(dup2(fd, STDIN_FILENO)) != STDIN_FILENO)
     63     return false;
     64   IGNORE_EINTR(close(fd));
     65 
     66   return true;
     67 }
     68 
     69 // Helper function to launch a process with the given Subprocess::Flags.
     70 // This function only sets up and starts the process according to the |flags|.
     71 // The caller is responsible for watching the termination of the subprocess.
     72 // Return whether the process was successfully launched and fills in the |proc|
     73 // Process.
     74 bool LaunchProcess(const vector<string>& cmd,
     75                    uint32_t flags,
     76                    const vector<int>& output_pipes,
     77                    brillo::Process* proc) {
     78   for (const string& arg : cmd)
     79     proc->AddArg(arg);
     80   proc->SetSearchPath((flags & Subprocess::kSearchPath) != 0);
     81 
     82   // Create an environment for the child process with just the required PATHs.
     83   std::map<string, string> env;
     84   for (const char* key : {"LD_LIBRARY_PATH", "PATH"}) {
     85     const char* value = getenv(key);
     86     if (value)
     87       env.emplace(key, value);
     88   }
     89 
     90   for (const int fd : output_pipes) {
     91     proc->RedirectUsingPipe(fd, false);
     92   }
     93   proc->SetCloseUnusedFileDescriptors(true);
     94   proc->RedirectUsingPipe(STDOUT_FILENO, false);
     95   proc->SetPreExecCallback(base::Bind(&SetupChild, env, flags));
     96 
     97   return proc->Start();
     98 }
     99 
    100 }  // namespace
    101 
    102 void Subprocess::Init(
    103       brillo::AsynchronousSignalHandlerInterface* async_signal_handler) {
    104   if (subprocess_singleton_ == this)
    105     return;
    106   CHECK(subprocess_singleton_ == nullptr);
    107   subprocess_singleton_ = this;
    108 
    109   process_reaper_.Register(async_signal_handler);
    110 }
    111 
    112 Subprocess::~Subprocess() {
    113   if (subprocess_singleton_ == this)
    114     subprocess_singleton_ = nullptr;
    115 }
    116 
    117 void Subprocess::OnStdoutReady(SubprocessRecord* record) {
    118   char buf[1024];
    119   size_t bytes_read;
    120   do {
    121     bytes_read = 0;
    122     bool eof;
    123     bool ok = utils::ReadAll(
    124         record->stdout_fd, buf, arraysize(buf), &bytes_read, &eof);
    125     record->stdout.append(buf, bytes_read);
    126     if (!ok || eof) {
    127       // There was either an error or an EOF condition, so we are done watching
    128       // the file descriptor.
    129       MessageLoop::current()->CancelTask(record->stdout_task_id);
    130       record->stdout_task_id = MessageLoop::kTaskIdNull;
    131       return;
    132     }
    133   } while (bytes_read);
    134 }
    135 
    136 void Subprocess::ChildExitedCallback(const siginfo_t& info) {
    137   auto pid_record = subprocess_records_.find(info.si_pid);
    138   if (pid_record == subprocess_records_.end())
    139     return;
    140   SubprocessRecord* record = pid_record->second.get();
    141 
    142   // Make sure we read any remaining process output and then close the pipe.
    143   OnStdoutReady(record);
    144 
    145   MessageLoop::current()->CancelTask(record->stdout_task_id);
    146   record->stdout_task_id = MessageLoop::kTaskIdNull;
    147 
    148   // Don't print any log if the subprocess exited with exit code 0.
    149   if (info.si_code != CLD_EXITED) {
    150     LOG(INFO) << "Subprocess terminated with si_code " << info.si_code;
    151   } else if (info.si_status != 0) {
    152     LOG(INFO) << "Subprocess exited with si_status: " << info.si_status;
    153   }
    154 
    155   if (!record->stdout.empty()) {
    156     LOG(INFO) << "Subprocess output:\n" << record->stdout;
    157   }
    158   if (!record->callback.is_null()) {
    159     record->callback.Run(info.si_status, record->stdout);
    160   }
    161   // Release and close all the pipes after calling the callback so our
    162   // redirected pipes are still alive. Releasing the process first makes
    163   // Reset(0) not attempt to kill the process, which is already a zombie at this
    164   // point.
    165   record->proc.Release();
    166   record->proc.Reset(0);
    167 
    168   subprocess_records_.erase(pid_record);
    169 }
    170 
    171 pid_t Subprocess::Exec(const vector<string>& cmd,
    172                        const ExecCallback& callback) {
    173   return ExecFlags(cmd, kRedirectStderrToStdout, {}, callback);
    174 }
    175 
    176 pid_t Subprocess::ExecFlags(const vector<string>& cmd,
    177                             uint32_t flags,
    178                             const vector<int>& output_pipes,
    179                             const ExecCallback& callback) {
    180   unique_ptr<SubprocessRecord> record(new SubprocessRecord(callback));
    181 
    182   if (!LaunchProcess(cmd, flags, output_pipes, &record->proc)) {
    183     LOG(ERROR) << "Failed to launch subprocess";
    184     return 0;
    185   }
    186 
    187   pid_t pid = record->proc.pid();
    188   CHECK(process_reaper_.WatchForChild(FROM_HERE, pid, base::Bind(
    189       &Subprocess::ChildExitedCallback,
    190       base::Unretained(this))));
    191 
    192   record->stdout_fd = record->proc.GetPipe(STDOUT_FILENO);
    193   // Capture the subprocess output. Make our end of the pipe non-blocking.
    194   int fd_flags = fcntl(record->stdout_fd, F_GETFL, 0) | O_NONBLOCK;
    195   if (HANDLE_EINTR(fcntl(record->stdout_fd, F_SETFL, fd_flags)) < 0) {
    196     LOG(ERROR) << "Unable to set non-blocking I/O mode on fd "
    197                << record->stdout_fd << ".";
    198   }
    199 
    200   record->stdout_task_id = MessageLoop::current()->WatchFileDescriptor(
    201       FROM_HERE,
    202       record->stdout_fd,
    203       MessageLoop::WatchMode::kWatchRead,
    204       true,
    205       base::Bind(&Subprocess::OnStdoutReady, record.get()));
    206 
    207   subprocess_records_[pid].reset(record.release());
    208   return pid;
    209 }
    210 
    211 void Subprocess::KillExec(pid_t pid) {
    212   auto pid_record = subprocess_records_.find(pid);
    213   if (pid_record == subprocess_records_.end())
    214     return;
    215   pid_record->second->callback.Reset();
    216   if (kill(pid, SIGTERM) != 0) {
    217     PLOG(WARNING) << "Error sending SIGTERM to " << pid;
    218   }
    219   // Release the pid now so we don't try to kill it if Subprocess is destroyed
    220   // before the corresponding ChildExitedCallback() is called.
    221   pid_record->second->proc.Release();
    222 }
    223 
    224 int Subprocess::GetPipeFd(pid_t pid, int fd) const {
    225   auto pid_record = subprocess_records_.find(pid);
    226   if (pid_record == subprocess_records_.end())
    227     return -1;
    228   return pid_record->second->proc.GetPipe(fd);
    229 }
    230 
    231 bool Subprocess::SynchronousExec(const vector<string>& cmd,
    232                                  int* return_code,
    233                                  string* stdout) {
    234   // The default for SynchronousExec is to use kSearchPath since the code relies
    235   // on that.
    236   return SynchronousExecFlags(
    237       cmd,
    238       kRedirectStderrToStdout | kSearchPath,
    239       return_code,
    240       stdout);
    241 }
    242 
    243 bool Subprocess::SynchronousExecFlags(const vector<string>& cmd,
    244                                       uint32_t flags,
    245                                       int* return_code,
    246                                       string* stdout) {
    247   brillo::ProcessImpl proc;
    248   // It doesn't make sense to redirect some pipes in the synchronous case
    249   // because we won't be reading on our end, so we don't expose the output_pipes
    250   // in this case.
    251   if (!LaunchProcess(cmd, flags, {}, &proc)) {
    252     LOG(ERROR) << "Failed to launch subprocess";
    253     return false;
    254   }
    255 
    256   if (stdout) {
    257     stdout->clear();
    258   }
    259 
    260   int fd = proc.GetPipe(STDOUT_FILENO);
    261   vector<char> buffer(32 * 1024);
    262   while (true) {
    263     int rc = HANDLE_EINTR(read(fd, buffer.data(), buffer.size()));
    264     if (rc < 0) {
    265       PLOG(ERROR) << "Reading from child's output";
    266       break;
    267     } else if (rc == 0) {
    268       break;
    269     } else {
    270       if (stdout)
    271         stdout->append(buffer.data(), rc);
    272     }
    273   }
    274   // At this point, the subprocess already closed the output, so we only need to
    275   // wait for it to finish.
    276   int proc_return_code = proc.Wait();
    277   if (return_code)
    278     *return_code = proc_return_code;
    279   return proc_return_code != brillo::Process::kErrorExitStatus;
    280 }
    281 
    282 bool Subprocess::SubprocessInFlight() {
    283   for (const auto& pid_record : subprocess_records_) {
    284     if (!pid_record.second->callback.is_null())
    285       return true;
    286   }
    287   return false;
    288 }
    289 
    290 Subprocess* Subprocess::subprocess_singleton_ = nullptr;
    291 
    292 }  // namespace chromeos_update_engine
    293