1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
|
//===- FuzzerUtilDarwin.cpp - Misc utils ----------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
// Misc utils for Darwin.
//===----------------------------------------------------------------------===//
#include "FuzzerPlatform.h"
#if LIBFUZZER_APPLE
#include "FuzzerCommand.h"
#include "FuzzerIO.h"
#include <mutex>
#include <signal.h>
#include <spawn.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <unistd.h>
// There is no header for this on macOS so declare here
extern "C" char **environ;
namespace fuzzer {
static std::mutex SignalMutex;
// Global variables used to keep track of how signal handling should be
// restored. They should **not** be accessed without holding `SignalMutex`.
static int ActiveThreadCount = 0;
static struct sigaction OldSigIntAction;
static struct sigaction OldSigQuitAction;
static sigset_t OldBlockedSignalsSet;
// This is a reimplementation of Libc's `system()`. On Darwin the Libc
// implementation contains a mutex which prevents it from being used
// concurrently. This implementation **can** be used concurrently. It sets the
// signal handlers when the first thread enters and restores them when the last
// thread finishes execution of the function and ensures this is not racey by
// using a mutex.
int ExecuteCommand(const Command &Cmd) {
std::string CmdLine = Cmd.toString();
posix_spawnattr_t SpawnAttributes;
if (posix_spawnattr_init(&SpawnAttributes))
return -1;
// Block and ignore signals of the current process when the first thread
// enters.
{
std::lock_guard<std::mutex> Lock(SignalMutex);
if (ActiveThreadCount == 0) {
static struct sigaction IgnoreSignalAction;
sigset_t BlockedSignalsSet;
memset(&IgnoreSignalAction, 0, sizeof(IgnoreSignalAction));
IgnoreSignalAction.sa_handler = SIG_IGN;
if (sigaction(SIGINT, &IgnoreSignalAction, &OldSigIntAction) == -1) {
Printf("Failed to ignore SIGINT\n");
(void)posix_spawnattr_destroy(&SpawnAttributes);
return -1;
}
if (sigaction(SIGQUIT, &IgnoreSignalAction, &OldSigQuitAction) == -1) {
Printf("Failed to ignore SIGQUIT\n");
// Try our best to restore the signal handlers.
(void)sigaction(SIGINT, &OldSigIntAction, NULL);
(void)posix_spawnattr_destroy(&SpawnAttributes);
return -1;
}
(void)sigemptyset(&BlockedSignalsSet);
(void)sigaddset(&BlockedSignalsSet, SIGCHLD);
if (sigprocmask(SIG_BLOCK, &BlockedSignalsSet, &OldBlockedSignalsSet) ==
-1) {
Printf("Failed to block SIGCHLD\n");
// Try our best to restore the signal handlers.
(void)sigaction(SIGQUIT, &OldSigQuitAction, NULL);
(void)sigaction(SIGINT, &OldSigIntAction, NULL);
(void)posix_spawnattr_destroy(&SpawnAttributes);
return -1;
}
}
++ActiveThreadCount;
}
// NOTE: Do not introduce any new `return` statements past this
// point. It is important that `ActiveThreadCount` always be decremented
// when leaving this function.
// Make sure the child process uses the default handlers for the
// following signals rather than inheriting what the parent has.
sigset_t DefaultSigSet;
(void)sigemptyset(&DefaultSigSet);
(void)sigaddset(&DefaultSigSet, SIGQUIT);
(void)sigaddset(&DefaultSigSet, SIGINT);
(void)posix_spawnattr_setsigdefault(&SpawnAttributes, &DefaultSigSet);
// Make sure the child process doesn't block SIGCHLD
(void)posix_spawnattr_setsigmask(&SpawnAttributes, &OldBlockedSignalsSet);
short SpawnFlags = POSIX_SPAWN_SETSIGDEF | POSIX_SPAWN_SETSIGMASK;
(void)posix_spawnattr_setflags(&SpawnAttributes, SpawnFlags);
pid_t Pid;
char **Environ = environ; // Read from global
const char *CommandCStr = CmdLine.c_str();
char *const Argv[] = {
strdup("sh"),
strdup("-c"),
strdup(CommandCStr),
NULL
};
int ErrorCode = 0, ProcessStatus = 0;
// FIXME: We probably shouldn't hardcode the shell path.
ErrorCode = posix_spawn(&Pid, "/bin/sh", NULL, &SpawnAttributes,
Argv, Environ);
(void)posix_spawnattr_destroy(&SpawnAttributes);
if (!ErrorCode) {
pid_t SavedPid = Pid;
do {
// Repeat until call completes uninterrupted.
Pid = waitpid(SavedPid, &ProcessStatus, /*options=*/0);
} while (Pid == -1 && errno == EINTR);
if (Pid == -1) {
// Fail for some other reason.
ProcessStatus = -1;
}
} else if (ErrorCode == ENOMEM || ErrorCode == EAGAIN) {
// Fork failure.
ProcessStatus = -1;
} else {
// Shell execution failure.
ProcessStatus = W_EXITCODE(127, 0);
}
for (unsigned i = 0, n = sizeof(Argv) / sizeof(Argv[0]); i < n; ++i)
free(Argv[i]);
// Restore the signal handlers of the current process when the last thread
// using this function finishes.
{
std::lock_guard<std::mutex> Lock(SignalMutex);
--ActiveThreadCount;
if (ActiveThreadCount == 0) {
bool FailedRestore = false;
if (sigaction(SIGINT, &OldSigIntAction, NULL) == -1) {
Printf("Failed to restore SIGINT handling\n");
FailedRestore = true;
}
if (sigaction(SIGQUIT, &OldSigQuitAction, NULL) == -1) {
Printf("Failed to restore SIGQUIT handling\n");
FailedRestore = true;
}
if (sigprocmask(SIG_BLOCK, &OldBlockedSignalsSet, NULL) == -1) {
Printf("Failed to unblock SIGCHLD\n");
FailedRestore = true;
}
if (FailedRestore)
ProcessStatus = -1;
}
}
return ProcessStatus;
}
void DiscardOutput(int Fd) {
FILE* Temp = fopen("/dev/null", "w");
if (!Temp)
return;
dup2(fileno(Temp), Fd);
fclose(Temp);
}
} // namespace fuzzer
#endif // LIBFUZZER_APPLE
|
