1 files changed, 212 insertions, 0 deletions
diff --git a/security/sandbox/linux/SandboxChroot.cpp b/security/sandbox/linux/SandboxChroot.cpp
new file mode 100644
index 000000000..2091bfe05
--- /dev/null
+++ b/security/sandbox/linux/SandboxChroot.cpp
@@ -0,0 +1,212 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "SandboxChroot.h"
+
+#include "SandboxLogging.h"
+#include "LinuxCapabilities.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "base/posix/eintr_wrapper.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/NullPtr.h"
+
+#define MOZ_ALWAYS_ZERO(e) MOZ_ALWAYS_TRUE((e) == 0)
+
+namespace mozilla {
+
+SandboxChroot::SandboxChroot()
+{
+  pthread_mutexattr_t attr;
+  MOZ_ALWAYS_ZERO(pthread_mutexattr_init(&attr));
+  MOZ_ALWAYS_ZERO(pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_ERRORCHECK));
+  MOZ_ALWAYS_ZERO(pthread_mutex_init(&mMutex, &attr));
+  MOZ_ALWAYS_ZERO(pthread_cond_init(&mWakeup, nullptr));
+  mCommand = NO_THREAD;
+}
+
+SandboxChroot::~SandboxChroot()
+{
+  SendCommand(JUST_EXIT);
+  MOZ_ALWAYS_ZERO(pthread_mutex_destroy(&mMutex));
+  MOZ_ALWAYS_ZERO(pthread_cond_destroy(&mWakeup));
+}
+
+bool
+SandboxChroot::SendCommand(Command aComm)
+{
+  MOZ_ALWAYS_ZERO(pthread_mutex_lock(&mMutex));
+  if (mCommand == NO_THREAD) {
+    MOZ_RELEASE_ASSERT(aComm == JUST_EXIT);
+    MOZ_ALWAYS_ZERO(pthread_mutex_unlock(&mMutex));
+    return false;
+  } else {
+    MOZ_ASSERT(mCommand == NO_COMMAND);
+    mCommand = aComm;
+    MOZ_ALWAYS_ZERO(pthread_mutex_unlock(&mMutex));
+    MOZ_ALWAYS_ZERO(pthread_cond_signal(&mWakeup));
+    void *retval;
+    if (pthread_join(mThread, &retval) != 0 || retval != nullptr) {
+      MOZ_CRASH("Failed to stop privileged chroot thread");
+    }
+    MOZ_ASSERT(mCommand == NO_THREAD);
+  }
+  return true;
+}
+
+static void
+AlwaysClose(int fd)
+{
+  if (IGNORE_EINTR(close(fd)) != 0) {
+    SANDBOX_LOG_ERROR("close: %s", strerror(errno));
+    MOZ_CRASH("failed to close()");
+  }
+}
+
+static int
+OpenDeletedDirectory()
+{
+  // We don't need this directory to persist between invocations of
+  // the program (nor need it to be cleaned up if something goes wrong
+  // here, because mkdtemp will choose a fresh name), so /tmp as
+  // specified by FHS is adequate.
+  //
+  // However, this needs a filesystem where a deleted directory can
+  // still be used, and /tmp is sometimes not that; e.g., aufs(5),
+  // often used for containers, will cause the chroot() to fail with
+  // ESTALE (bug 1162965).  So this uses /dev/shm if possible instead.
+  char tmpPath[] = "/tmp/mozsandbox.XXXXXX";
+  char shmPath[] = "/dev/shm/mozsandbox.XXXXXX";
+  char* path;
+  if (mkdtemp(shmPath)) {
+    path = shmPath;
+  } else if (mkdtemp(tmpPath)) {
+    path = tmpPath;
+  } else {
+    SANDBOX_LOG_ERROR("mkdtemp: %s", strerror(errno));
+    return -1;
+  }
+  int fd = HANDLE_EINTR(open(path, O_RDONLY | O_DIRECTORY));
+  if (fd < 0) {
+    SANDBOX_LOG_ERROR("open %s: %s", path, strerror(errno));
+    // Try to clean up.  Shouldn't fail, but livable if it does.
+    DebugOnly<bool> ok = HANDLE_EINTR(rmdir(path)) == 0;
+    MOZ_ASSERT(ok);
+    return -1;
+  }
+  if (HANDLE_EINTR(rmdir(path)) != 0) {
+    SANDBOX_LOG_ERROR("rmdir %s: %s", path, strerror(errno));
+    AlwaysClose(fd);
+    return -1;
+  }
+  return fd;
+}
+
+bool
+SandboxChroot::Prepare()
+{
+  LinuxCapabilities caps;
+  if (!caps.GetCurrent() || !caps.Effective(CAP_SYS_CHROOT)) {
+    SANDBOX_LOG_ERROR("don't have permission to chroot");
+    return false;
+  }
+  mFd = OpenDeletedDirectory();
+  if (mFd < 0) {
+    SANDBOX_LOG_ERROR("failed to create empty directory for chroot");
+    return false;
+  }
+  MOZ_ALWAYS_ZERO(pthread_mutex_lock(&mMutex));
+  MOZ_ASSERT(mCommand == NO_THREAD);
+  if (pthread_create(&mThread, nullptr, StaticThreadMain, this) != 0) {
+    MOZ_ALWAYS_ZERO(pthread_mutex_unlock(&mMutex));
+    SANDBOX_LOG_ERROR("pthread_create: %s", strerror(errno));
+    return false;
+  }
+  while (mCommand != NO_COMMAND) {
+    MOZ_ASSERT(mCommand == NO_THREAD);
+    MOZ_ALWAYS_ZERO(pthread_cond_wait(&mWakeup, &mMutex));
+  }
+  MOZ_ALWAYS_ZERO(pthread_mutex_unlock(&mMutex));
+  return true;
+}
+
+void
+SandboxChroot::Invoke()
+{
+  MOZ_ALWAYS_TRUE(SendCommand(DO_CHROOT));
+}
+
+static bool
+ChrootToFileDesc(int fd)
+{
+  if (fchdir(fd) != 0) {
+    SANDBOX_LOG_ERROR("fchdir: %s", strerror(errno));
+    return false;
+  }
+  if (chroot(".") != 0) {
+    SANDBOX_LOG_ERROR("chroot: %s", strerror(errno));
+    return false;
+  }
+  return true;
+}
+
+/* static */ void*
+SandboxChroot::StaticThreadMain(void* aVoidPtr)
+{
+  static_cast<SandboxChroot*>(aVoidPtr)->ThreadMain();
+  return nullptr;
+}
+
+void
+SandboxChroot::ThreadMain()
+{
+  // First, drop everything that isn't CAP_SYS_CHROOT.  (This code
+  // assumes that this thread already has effective CAP_SYS_CHROOT,
+  // because Prepare() checked for it before creating this thread.)
+  LinuxCapabilities caps;
+  caps.Effective(CAP_SYS_CHROOT) = true;
+  if (!caps.SetCurrent()) {
+    SANDBOX_LOG_ERROR("capset: %s", strerror(errno));
+    MOZ_CRASH("Can't limit chroot thread's capabilities");
+  }
+
+  MOZ_ALWAYS_ZERO(pthread_mutex_lock(&mMutex));
+  MOZ_ASSERT(mCommand == NO_THREAD);
+  mCommand = NO_COMMAND;
+  MOZ_ALWAYS_ZERO(pthread_cond_signal(&mWakeup));
+  while (mCommand == NO_COMMAND) {
+    MOZ_ALWAYS_ZERO(pthread_cond_wait(&mWakeup, &mMutex));
+  }
+  if (mCommand == DO_CHROOT) {
+    MOZ_ASSERT(mFd >= 0);
+    if (!ChrootToFileDesc(mFd)) {
+      MOZ_CRASH("Failed to chroot");
+    }
+  } else {
+    MOZ_ASSERT(mCommand == JUST_EXIT);
+  }
+  if (mFd >= 0) {
+    AlwaysClose(mFd);
+    mFd = -1;
+  }
+  mCommand = NO_THREAD;
+  MOZ_ALWAYS_ZERO(pthread_mutex_unlock(&mMutex));
+  // Drop the remaining capabilities; see note in SandboxChroot.h
+  // about the potential unreliability of pthread_join.
+  if (!LinuxCapabilities().SetCurrent()) {
+    MOZ_CRASH("can't drop capabilities");
+  }
+}
+
+} // namespace mozilla
+
+#undef MOZ_ALWAYS_ZERO