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// Copyright 2015 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "sandbox/policy/linux/sandbox_debug_handling_linux.h"
#include <errno.h>
#include <signal.h>
#include <stddef.h>
#include <sys/prctl.h>
#include <unistd.h>
#include <tuple>
#include "base/check.h"
#include "base/check_op.h"
#include "base/command_line.h"
#include "base/logging.h"
#include "base/strings/safe_sprintf.h"
#include "sandbox/policy/switches.h"
namespace sandbox {
namespace policy {
namespace {
void DoChrootSignalHandler(int) {
const int old_errno = errno;
const char kFirstMessage[] = "Chroot signal handler called.\n";
std::ignore = write(STDERR_FILENO, kFirstMessage, sizeof(kFirstMessage) - 1);
const int chroot_ret = chroot("/");
char kSecondMessage[100];
const ssize_t printed = base::strings::SafeSPrintf(
kSecondMessage, "chroot() returned %d. Errno is %d.\n", chroot_ret,
errno);
if (printed > 0 && printed < static_cast<ssize_t>(sizeof(kSecondMessage))) {
std::ignore = write(STDERR_FILENO, kSecondMessage, printed);
}
errno = old_errno;
}
// This is a quick hack to allow testing sandbox crash reports in production
// binaries.
// This installs a signal handler for SIGUSR2 that performs a chroot().
// In most of our BPF policies, it is a "watched" system call which will
// trigger a SIGSYS signal whose handler will crash.
// This has been added during the investigation of https://crbug.com/415842.
void InstallCrashTestHandler() {
struct sigaction act = {};
act.sa_handler = DoChrootSignalHandler;
CHECK_EQ(0, sigemptyset(&act.sa_mask));
act.sa_flags = 0;
PCHECK(0 == sigaction(SIGUSR2, &act, NULL));
}
bool IsSandboxDebuggingEnabled() {
return base::CommandLine::ForCurrentProcess()->HasSwitch(
switches::kAllowSandboxDebugging);
}
} // namespace
// static
bool SandboxDebugHandling::SetDumpableStatusAndHandlers() {
if (IsSandboxDebuggingEnabled()) {
// If sandbox debugging is allowed, install a handler for sandbox-related
// crash testing.
InstallCrashTestHandler();
return true;
}
if (prctl(PR_SET_DUMPABLE, 0) != 0) {
PLOG(ERROR) << "Failed to set non-dumpable flag";
return false;
}
return prctl(PR_GET_DUMPABLE) == 0;
}
} // namespace policy
} // namespace sandbox
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