1 //===-- ProcessLauncherPosixFork.cpp --------------------------------------===//
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 <climits>
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 
37 using namespace lldb;
38 using namespace lldb_private;
39 
40 static 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 
49 static 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 
58 static 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 
73 static 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 
91 static 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 
178 HostProcess
179 ProcessLauncherPosixFork::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