1//===- FuzzerUtilDarwin.cpp - Misc utils ----------------------------------===//
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// Misc utils for Darwin.
9//===----------------------------------------------------------------------===//
10#include "FuzzerPlatform.h"
11#if LIBFUZZER_APPLE
12#include "FuzzerCommand.h"
13#include "FuzzerIO.h"
14#include <mutex>
15#include <signal.h>
16#include <spawn.h>
17#include <stdlib.h>
18#include <string.h>
19#include <sys/wait.h>
20#include <unistd.h>
21
22// There is no header for this on macOS so declare here
23extern "C" char **environ;
24
25namespace fuzzer {
26
27static std::mutex SignalMutex;
28// Global variables used to keep track of how signal handling should be
29// restored. They should **not** be accessed without holding `SignalMutex`.
30static int ActiveThreadCount = 0;
31static struct sigaction OldSigIntAction;
32static struct sigaction OldSigQuitAction;
33static sigset_t OldBlockedSignalsSet;
34
35// This is a reimplementation of Libc's `system()`. On Darwin the Libc
36// implementation contains a mutex which prevents it from being used
37// concurrently. This implementation **can** be used concurrently. It sets the
38// signal handlers when the first thread enters and restores them when the last
39// thread finishes execution of the function and ensures this is not racey by
40// using a mutex.
41int ExecuteCommand(const Command &Cmd) {
42 std::string CmdLine = Cmd.toString();
43 posix_spawnattr_t SpawnAttributes;
44 if (posix_spawnattr_init(&SpawnAttributes))
45 return -1;
46 // Block and ignore signals of the current process when the first thread
47 // enters.
48 {
49 std::lock_guard<std::mutex> Lock(SignalMutex);
50 if (ActiveThreadCount == 0) {
51 static struct sigaction IgnoreSignalAction;
52 sigset_t BlockedSignalsSet;
53 memset(&IgnoreSignalAction, 0, sizeof(IgnoreSignalAction));
54 IgnoreSignalAction.sa_handler = SIG_IGN;
55
56 if (sigaction(SIGINT, &IgnoreSignalAction, &OldSigIntAction) == -1) {
57 Printf("Failed to ignore SIGINT\n");
58 (void)posix_spawnattr_destroy(&SpawnAttributes);
59 return -1;
60 }
61 if (sigaction(SIGQUIT, &IgnoreSignalAction, &OldSigQuitAction) == -1) {
62 Printf("Failed to ignore SIGQUIT\n");
63 // Try our best to restore the signal handlers.
64 (void)sigaction(SIGINT, &OldSigIntAction, NULL);
65 (void)posix_spawnattr_destroy(&SpawnAttributes);
66 return -1;
67 }
68
69 (void)sigemptyset(&BlockedSignalsSet);
70 (void)sigaddset(&BlockedSignalsSet, SIGCHLD);
71 if (sigprocmask(SIG_BLOCK, &BlockedSignalsSet, &OldBlockedSignalsSet) ==
72 -1) {
73 Printf("Failed to block SIGCHLD\n");
74 // Try our best to restore the signal handlers.
75 (void)sigaction(SIGQUIT, &OldSigQuitAction, NULL);
76 (void)sigaction(SIGINT, &OldSigIntAction, NULL);
77 (void)posix_spawnattr_destroy(&SpawnAttributes);
78 return -1;
79 }
80 }
81 ++ActiveThreadCount;
82 }
83
84 // NOTE: Do not introduce any new `return` statements past this
85 // point. It is important that `ActiveThreadCount` always be decremented
86 // when leaving this function.
87
88 // Make sure the child process uses the default handlers for the
89 // following signals rather than inheriting what the parent has.
90 sigset_t DefaultSigSet;
91 (void)sigemptyset(&DefaultSigSet);
92 (void)sigaddset(&DefaultSigSet, SIGQUIT);
93 (void)sigaddset(&DefaultSigSet, SIGINT);
94 (void)posix_spawnattr_setsigdefault(&SpawnAttributes, &DefaultSigSet);
95 // Make sure the child process doesn't block SIGCHLD
96 (void)posix_spawnattr_setsigmask(&SpawnAttributes, &OldBlockedSignalsSet);
97 short SpawnFlags = POSIX_SPAWN_SETSIGDEF | POSIX_SPAWN_SETSIGMASK;
98 (void)posix_spawnattr_setflags(&SpawnAttributes, SpawnFlags);
99
100 pid_t Pid;
101 char **Environ = environ; // Read from global
102 const char *CommandCStr = CmdLine.c_str();
103 char *const Argv[] = {
104 strdup("sh"),
105 strdup("-c"),
106 strdup(CommandCStr),
107 NULL
108 };
109 int ErrorCode = 0, ProcessStatus = 0;
110 // FIXME: We probably shouldn't hardcode the shell path.
111 ErrorCode = posix_spawn(&Pid, "/bin/sh", NULL, &SpawnAttributes,
112 Argv, Environ);
113 (void)posix_spawnattr_destroy(&SpawnAttributes);
114 if (!ErrorCode) {
115 pid_t SavedPid = Pid;
116 do {
117 // Repeat until call completes uninterrupted.
118 Pid = waitpid(SavedPid, &ProcessStatus, /*options=*/0);
119 } while (Pid == -1 && errno == EINTR);
120 if (Pid == -1) {
121 // Fail for some other reason.
122 ProcessStatus = -1;
123 }
124 } else if (ErrorCode == ENOMEM || ErrorCode == EAGAIN) {
125 // Fork failure.
126 ProcessStatus = -1;
127 } else {
128 // Shell execution failure.
129 ProcessStatus = W_EXITCODE(127, 0);
130 }
131 for (unsigned i = 0, n = sizeof(Argv) / sizeof(Argv[0]); i < n; ++i)
132 free(Argv[i]);
133
134 // Restore the signal handlers of the current process when the last thread
135 // using this function finishes.
136 {
137 std::lock_guard<std::mutex> Lock(SignalMutex);
138 --ActiveThreadCount;
139 if (ActiveThreadCount == 0) {
140 bool FailedRestore = false;
141 if (sigaction(SIGINT, &OldSigIntAction, NULL) == -1) {
142 Printf("Failed to restore SIGINT handling\n");
143 FailedRestore = true;
144 }
145 if (sigaction(SIGQUIT, &OldSigQuitAction, NULL) == -1) {
146 Printf("Failed to restore SIGQUIT handling\n");
147 FailedRestore = true;
148 }
149 if (sigprocmask(SIG_BLOCK, &OldBlockedSignalsSet, NULL) == -1) {
150 Printf("Failed to unblock SIGCHLD\n");
151 FailedRestore = true;
152 }
153 if (FailedRestore)
154 ProcessStatus = -1;
155 }
156 }
157 return ProcessStatus;
158}
159
160void DiscardOutput(int Fd) {
161 FILE* Temp = fopen("/dev/null", "w");
162 if (!Temp)
163 return;
164 dup2(fileno(Temp), Fd);
165 fclose(Temp);
166}
167
168void SetThreadName(std::thread &thread, const std::string &name) {
169 // TODO ?
170 // Darwin allows to set the name only on the current thread it seems
171}
172
173} // namespace fuzzer
174
175#endif // LIBFUZZER_APPLE
176

source code of compiler-rt/lib/fuzzer/FuzzerUtilDarwin.cpp