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//===- FuzzerUtilDarwin.cpp - Misc utils ----------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// 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