1//===-- ProcessLauncherPosixFork.cpp ----------------------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#include "lldb/Host/posix/ProcessLauncherPosixFork.h"
10#include "lldb/Host/Host.h"
11#include "lldb/Host/HostProcess.h"
12#include "lldb/Host/Pipe.h"
13#include "lldb/Host/ProcessLaunchInfo.h"
14#include "lldb/Utility/FileSpec.h"
15#include "lldb/Utility/Log.h"
16#include "llvm/Support/Errno.h"
17
18#include <limits.h>
19#include <sys/ptrace.h>
20#include <sys/wait.h>
21#include <unistd.h>
22
23#include <sstream>
24#include <csignal>
25
26#ifdef __ANDROID__
27#include <android/api-level.h>
28#define PT_TRACE_ME PTRACE_TRACEME
29#endif
30
31#if defined(__ANDROID_API__) && __ANDROID_API__ < 15
32#include <linux/personality.h>
33#elif defined(__linux__)
34#include <sys/personality.h>
35#endif
36
37using namespace lldb;
38using namespace lldb_private;
39
40static void FixupEnvironment(Environment &env) {
41#ifdef __ANDROID__
42  // If there is no PATH variable specified inside the environment then set the
43  // path to /system/bin. It is required because the default path used by
44  // execve() is wrong on android.
45  env.try_emplace("PATH", "/system/bin");
46#endif
47}
48
49static void LLVM_ATTRIBUTE_NORETURN ExitWithError(int error_fd,
50                                                  const char *operation) {
51  int err = errno;
52  llvm::raw_fd_ostream os(error_fd, true);
53  os << operation << " failed: " << llvm::sys::StrError(err);
54  os.flush();
55  _exit(1);
56}
57
58static void DisableASLRIfRequested(int error_fd, const ProcessLaunchInfo &info) {
59#if defined(__linux__)
60  if (info.GetFlags().Test(lldb::eLaunchFlagDisableASLR)) {
61    const unsigned long personality_get_current = 0xffffffff;
62    int value = personality(personality_get_current);
63    if (value == -1)
64      ExitWithError(error_fd, "personality get");
65
66    value = personality(ADDR_NO_RANDOMIZE | value);
67    if (value == -1)
68      ExitWithError(error_fd, "personality set");
69  }
70#endif
71}
72
73static void DupDescriptor(int error_fd, const FileSpec &file_spec, int fd,
74                          int flags) {
75  int target_fd = llvm::sys::RetryAfterSignal(-1, ::open,
76      file_spec.GetCString(), flags, 0666);
77
78  if (target_fd == -1)
79    ExitWithError(error_fd, "DupDescriptor-open");
80
81  if (target_fd == fd)
82    return;
83
84  if (::dup2(target_fd, fd) == -1)
85    ExitWithError(error_fd, "DupDescriptor-dup2");
86
87  ::close(target_fd);
88  return;
89}
90
91static void LLVM_ATTRIBUTE_NORETURN ChildFunc(int error_fd,
92                                              const ProcessLaunchInfo &info) {
93  if (info.GetFlags().Test(eLaunchFlagLaunchInSeparateProcessGroup)) {
94    if (setpgid(0, 0) != 0)
95      ExitWithError(error_fd, "setpgid");
96  }
97
98  for (size_t i = 0; i < info.GetNumFileActions(); ++i) {
99    const FileAction &action = *info.GetFileActionAtIndex(i);
100    switch (action.GetAction()) {
101    case FileAction::eFileActionClose:
102      if (close(action.GetFD()) != 0)
103        ExitWithError(error_fd, "close");
104      break;
105    case FileAction::eFileActionDuplicate:
106      if (dup2(action.GetFD(), action.GetActionArgument()) == -1)
107        ExitWithError(error_fd, "dup2");
108      break;
109    case FileAction::eFileActionOpen:
110      DupDescriptor(error_fd, action.GetFileSpec(), action.GetFD(),
111                    action.GetActionArgument());
112      break;
113    case FileAction::eFileActionNone:
114      break;
115    }
116  }
117
118  const char **argv = info.GetArguments().GetConstArgumentVector();
119
120  // Change working directory
121  if (info.GetWorkingDirectory() &&
122      0 != ::chdir(info.GetWorkingDirectory().GetCString()))
123    ExitWithError(error_fd, "chdir");
124
125  DisableASLRIfRequested(error_fd, info);
126  Environment env = info.GetEnvironment();
127  FixupEnvironment(env);
128  Environment::Envp envp = env.getEnvp();
129
130  // Clear the signal mask to prevent the child from being affected by any
131  // masking done by the parent.
132  sigset_t set;
133  if (sigemptyset(&set) != 0 ||
134      pthread_sigmask(SIG_SETMASK, &set, nullptr) != 0)
135    ExitWithError(error_fd, "pthread_sigmask");
136
137  if (info.GetFlags().Test(eLaunchFlagDebug)) {
138    // Do not inherit setgid powers.
139    if (setgid(getgid()) != 0)
140      ExitWithError(error_fd, "setgid");
141
142    // HACK:
143    // Close everything besides stdin, stdout, and stderr that has no file
144    // action to avoid leaking. Only do this when debugging, as elsewhere we
145    // actually rely on passing open descriptors to child processes.
146    for (int fd = 3; fd < sysconf(_SC_OPEN_MAX); ++fd)
147      if (!info.GetFileActionForFD(fd) && fd != error_fd)
148        close(fd);
149
150    // Start tracing this child that is about to exec.
151    if (ptrace(PT_TRACE_ME, 0, nullptr, 0) == -1)
152      ExitWithError(error_fd, "ptrace");
153  }
154
155  // Execute.  We should never return...
156  execve(argv[0], const_cast<char *const *>(argv), envp);
157
158#if defined(__linux__)
159  if (errno == ETXTBSY) {
160    // On android M and earlier we can get this error because the adb daemon
161    // can hold a write handle on the executable even after it has finished
162    // uploading it. This state lasts only a short time and happens only when
163    // there are many concurrent adb commands being issued, such as when
164    // running the test suite. (The file remains open when someone does an "adb
165    // shell" command in the fork() child before it has had a chance to exec.)
166    // Since this state should clear up quickly, wait a while and then give it
167    // one more go.
168    usleep(50000);
169    execve(argv[0], const_cast<char *const *>(argv), envp);
170  }
171#endif
172
173  // ...unless exec fails.  In which case we definitely need to end the child
174  // here.
175  ExitWithError(error_fd, "execve");
176}
177
178HostProcess
179ProcessLauncherPosixFork::LaunchProcess(const ProcessLaunchInfo &launch_info,
180                                        Status &error) {
181  char exe_path[PATH_MAX];
182  launch_info.GetExecutableFile().GetPath(exe_path, sizeof(exe_path));
183
184  // A pipe used by the child process to report errors.
185  PipePosix pipe;
186  const bool child_processes_inherit = false;
187  error = pipe.CreateNew(child_processes_inherit);
188  if (error.Fail())
189    return HostProcess();
190
191  ::pid_t pid = ::fork();
192  if (pid == -1) {
193    // Fork failed
194    error.SetErrorStringWithFormatv("Fork failed with error message: {0}",
195                                    llvm::sys::StrError());
196    return HostProcess(LLDB_INVALID_PROCESS_ID);
197  }
198  if (pid == 0) {
199    // child process
200    pipe.CloseReadFileDescriptor();
201    ChildFunc(pipe.ReleaseWriteFileDescriptor(), launch_info);
202  }
203
204  // parent process
205
206  pipe.CloseWriteFileDescriptor();
207  char buf[1000];
208  int r = read(pipe.GetReadFileDescriptor(), buf, sizeof buf);
209
210  if (r == 0)
211    return HostProcess(pid); // No error. We're done.
212
213  error.SetErrorString(buf);
214
215  llvm::sys::RetryAfterSignal(-1, waitpid, pid, nullptr, 0);
216
217  return HostProcess();
218}
219