Update from chromium 62675d9fb31fb8cedc40f68e78e8445a74f362e7

sandbox/linux/services/broker_process.cc

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "sandbox/linux/services/broker_process.h"
+
+#include <fcntl.h>
+#include <signal.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include <algorithm>
+#include <string>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/callback.h"
+#include "base/compiler_specific.h"
+#include "base/files/scoped_file.h"
+#include "base/logging.h"
+#include "base/memory/scoped_vector.h"
+#include "base/pickle.h"
+#include "base/posix/eintr_wrapper.h"
+#include "base/posix/unix_domain_socket_linux.h"
+#include "base/process/process_metrics.h"
+#include "base/third_party/valgrind/valgrind.h"
+#include "build/build_config.h"
+#include "sandbox/linux/services/linux_syscalls.h"
+
+#if defined(OS_ANDROID) && !defined(MSG_CMSG_CLOEXEC)
+#define MSG_CMSG_CLOEXEC 0x40000000
+#endif
+
+namespace {
+
+bool IsRunningOnValgrind() { return RUNNING_ON_VALGRIND; }
+
+// A little open(2) wrapper to handle some oddities for us. In the general case
+// make a direct system call since we want to keep in control of the broker
+// process' system calls profile to be able to loosely sandbox it.
+int sys_open(const char* pathname, int flags) {
+  // Always pass a defined |mode| in case flags mistakenly contains O_CREAT.
+  const int mode = 0;
+  if (IsRunningOnValgrind()) {
+    // Valgrind does not support AT_FDCWD, just use libc's open() in this case.
+    return open(pathname, flags, mode);
+  } else {
+    return syscall(__NR_openat, AT_FDCWD, pathname, flags, mode);
+  }
+}
+
+static const size_t kMaxMessageLength = 4096;
+
+// Some flags are local to the current process and cannot be sent over a Unix
+// socket. They need special treatment from the client.
+// O_CLOEXEC is tricky because in theory another thread could call execve()
+// before special treatment is made on the client, so a client needs to call
+// recvmsg(2) with MSG_CMSG_CLOEXEC.
+// To make things worse, there are two CLOEXEC related flags, FD_CLOEXEC (see
+// F_GETFD in fcntl(2)) and O_CLOEXEC (see F_GETFL in fcntl(2)). O_CLOEXEC
+// doesn't affect the semantics on execve(), it's merely a note that the
+// descriptor was originally opened with O_CLOEXEC as a flag. And it is sent
+// over unix sockets just fine, so a receiver that would (incorrectly) look at
+// O_CLOEXEC instead of FD_CLOEXEC may be tricked in thinking that the file
+// descriptor will or won't be closed on execve().
+static const int kCurrentProcessOpenFlagsMask = O_CLOEXEC;
+
+// Check whether |requested_filename| is in |allowed_file_names|.
+// See GetFileNameIfAllowedToOpen() for an explanation of |file_to_open|.
+// async signal safe if |file_to_open| is NULL.
+// TODO(jln): assert signal safety.
+bool GetFileNameInWhitelist(const std::vector<std::string>& allowed_file_names,
+                            const char* requested_filename,
+                            const char** file_to_open) {
+  if (file_to_open && *file_to_open) {
+    // Make sure that callers never pass a non-empty string. In case callers
+    // wrongly forget to check the return value and look at the string
+    // instead, this could catch bugs.
+    RAW_LOG(FATAL, "*file_to_open should be NULL");
+    return false;
+  }
+
+  // Look for |requested_filename| in |allowed_file_names|.
+  // We don't use ::find() because it takes a std::string and
+  // the conversion allocates memory.
+  std::vector<std::string>::const_iterator it;
+  for (it = allowed_file_names.begin(); it != allowed_file_names.end(); it++) {
+    if (strcmp(requested_filename, it->c_str()) == 0) {
+      if (file_to_open)
+        *file_to_open = it->c_str();
+      return true;
+    }
+  }
+  return false;
+}
+
+// We maintain a list of flags that have been reviewed for "sanity" and that
+// we're ok to allow in the broker.
+// I.e. here is where we wouldn't add O_RESET_FILE_SYSTEM.
+bool IsAllowedOpenFlags(int flags) {
+  // First, check the access mode.
+  const int access_mode = flags & O_ACCMODE;
+  if (access_mode != O_RDONLY && access_mode != O_WRONLY &&
+      access_mode != O_RDWR) {
+    return false;
+  }
+
+  // We only support a 2-parameters open, so we forbid O_CREAT.
+  if (flags & O_CREAT) {
+    return false;
+  }
+
+  // Some flags affect the behavior of the current process. We don't support
+  // them and don't allow them for now.
+  if (flags & kCurrentProcessOpenFlagsMask)
+    return false;
+
+  // Now check that all the flags are known to us.
+  const int creation_and_status_flags = flags & ~O_ACCMODE;
+
+  const int known_flags =
+    O_APPEND | O_ASYNC | O_CLOEXEC | O_CREAT | O_DIRECT |
+    O_DIRECTORY | O_EXCL | O_LARGEFILE | O_NOATIME | O_NOCTTY |
+    O_NOFOLLOW | O_NONBLOCK | O_NDELAY | O_SYNC | O_TRUNC;
+
+  const int unknown_flags = ~known_flags;
+  const bool has_unknown_flags = creation_and_status_flags & unknown_flags;
+  return !has_unknown_flags;
+}
+
+}  // namespace
+
+namespace sandbox {
+
+BrokerProcess::BrokerProcess(int denied_errno,
+                             const std::vector<std::string>& allowed_r_files,
+                             const std::vector<std::string>& allowed_w_files,
+                             bool fast_check_in_client,
+                             bool quiet_failures_for_tests)
+    : denied_errno_(denied_errno),
+      initialized_(false),
+      is_child_(false),
+      fast_check_in_client_(fast_check_in_client),
+      quiet_failures_for_tests_(quiet_failures_for_tests),
+      broker_pid_(-1),
+      allowed_r_files_(allowed_r_files),
+      allowed_w_files_(allowed_w_files),
+      ipc_socketpair_(-1) {
+}
+
+BrokerProcess::~BrokerProcess() {
+  if (initialized_ && ipc_socketpair_ != -1) {
+    // Closing the socket should be enough to notify the child to die,
+    // unless it has been duplicated.
+    PCHECK(0 == IGNORE_EINTR(close(ipc_socketpair_)));
+    PCHECK(0 == kill(broker_pid_, SIGKILL));
+    siginfo_t process_info;
+    // Reap the child.
+    int ret = HANDLE_EINTR(waitid(P_PID, broker_pid_, &process_info, WEXITED));
+    PCHECK(0 == ret);
+  }
+}
+
+bool BrokerProcess::Init(
+    const base::Callback<bool(void)>& broker_process_init_callback) {
+  CHECK(!initialized_);
+  int socket_pair[2];
+  // Use SOCK_SEQPACKET, because we need to preserve message boundaries
+  // but we also want to be notified (recvmsg should return and not block)
+  // when the connection has been broken (one of the processes died).
+  if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, socket_pair)) {
+    LOG(ERROR) << "Failed to create socketpair";
+    return false;
+  }
+
+#if !defined(THREAD_SANITIZER)
+  DCHECK_EQ(1, base::GetNumberOfThreads(base::GetCurrentProcessHandle()));
+#endif
+  int child_pid = fork();
+  if (child_pid == -1) {
+    close(socket_pair[0]);
+    close(socket_pair[1]);
+    return false;
+  }
+  if (child_pid) {
+    // We are the parent and we have just forked our broker process.
+    close(socket_pair[0]);
+    // We should only be able to write to the IPC channel. We'll always send
+    // a new file descriptor to receive the reply on.
+    shutdown(socket_pair[1], SHUT_RD);
+    ipc_socketpair_ = socket_pair[1];
+    is_child_ = false;
+    broker_pid_ = child_pid;
+    initialized_ = true;
+    return true;
+  } else {
+    // We are the broker.
+    close(socket_pair[1]);
+    // We should only be able to read from this IPC channel. We will send our
+    // replies on a new file descriptor attached to the requests.
+    shutdown(socket_pair[0], SHUT_WR);
+    ipc_socketpair_ = socket_pair[0];
+    is_child_ = true;
+    CHECK(broker_process_init_callback.Run());
+    initialized_ = true;
+    for (;;) {
+      HandleRequest();
+    }
+    _exit(1);
+  }
+  NOTREACHED();
+}
+
+int BrokerProcess::Access(const char* pathname, int mode) const {
+  return PathAndFlagsSyscall(kCommandAccess, pathname, mode);
+}
+
+int BrokerProcess::Open(const char* pathname, int flags) const {
+  return PathAndFlagsSyscall(kCommandOpen, pathname, flags);
+}
+
+// Make a remote system call over IPC for syscalls that take a path and flags
+// as arguments, currently open() and access().
+// Will return -errno like a real system call.
+// This function needs to be async signal safe.
+int BrokerProcess::PathAndFlagsSyscall(enum IPCCommands syscall_type,
+                                       const char* pathname, int flags) const {
+  int recvmsg_flags = 0;
+  RAW_CHECK(initialized_);  // async signal safe CHECK().
+  RAW_CHECK(syscall_type == kCommandOpen || syscall_type == kCommandAccess);
+  if (!pathname)
+    return -EFAULT;
+
+  // For this "remote system call" to work, we need to handle any flag that
+  // cannot be sent over a Unix socket in a special way.
+  // See the comments around kCurrentProcessOpenFlagsMask.
+  if (syscall_type == kCommandOpen && (flags & kCurrentProcessOpenFlagsMask)) {
+    // This implementation only knows about O_CLOEXEC, someone needs to look at
+    // this code if other flags are added.
+    RAW_CHECK(kCurrentProcessOpenFlagsMask == O_CLOEXEC);
+    recvmsg_flags |= MSG_CMSG_CLOEXEC;
+    flags &= ~O_CLOEXEC;
+  }
+
+  // There is no point in forwarding a request that we know will be denied.
+  // Of course, the real security check needs to be on the other side of the
+  // IPC.
+  if (fast_check_in_client_) {
+    if (syscall_type == kCommandOpen &&
+        !GetFileNameIfAllowedToOpen(pathname, flags, NULL)) {
+      return -denied_errno_;
+    }
+    if (syscall_type == kCommandAccess &&
+        !GetFileNameIfAllowedToAccess(pathname, flags, NULL)) {
+      return -denied_errno_;
+    }
+  }
+
+  Pickle write_pickle;
+  write_pickle.WriteInt(syscall_type);
+  write_pickle.WriteString(pathname);
+  write_pickle.WriteInt(flags);
+  RAW_CHECK(write_pickle.size() <= kMaxMessageLength);
+
+  int returned_fd = -1;
+  uint8_t reply_buf[kMaxMessageLength];
+
+  // Send a request (in write_pickle) as well that will include a new
+  // temporary socketpair (created internally by SendRecvMsg()).
+  // Then read the reply on this new socketpair in reply_buf and put an
+  // eventual attached file descriptor in |returned_fd|.
+  ssize_t msg_len = UnixDomainSocket::SendRecvMsgWithFlags(ipc_socketpair_,
+                                                           reply_buf,
+                                                           sizeof(reply_buf),
+                                                           recvmsg_flags,
+                                                           &returned_fd,
+                                                           write_pickle);
+  if (msg_len <= 0) {
+    if (!quiet_failures_for_tests_)
+      RAW_LOG(ERROR, "Could not make request to broker process");
+    return -ENOMEM;
+  }
+
+  Pickle read_pickle(reinterpret_cast<char*>(reply_buf), msg_len);
+  PickleIterator iter(read_pickle);
+  int return_value = -1;
+  // Now deserialize the return value and eventually return the file
+  // descriptor.
+  if (read_pickle.ReadInt(&iter, &return_value)) {
+    switch (syscall_type) {
+      case kCommandAccess:
+        // We should never have a fd to return.
+        RAW_CHECK(returned_fd == -1);
+        return return_value;
+      case kCommandOpen:
+        if (return_value < 0) {
+          RAW_CHECK(returned_fd == -1);
+          return return_value;
+        } else {
+          // We have a real file descriptor to return.
+          RAW_CHECK(returned_fd >= 0);
+          return returned_fd;
+        }
+      default:
+        RAW_LOG(ERROR, "Unsupported command");
+        return -ENOSYS;
+    }
+  } else {
+    RAW_LOG(ERROR, "Could not read pickle");
+    NOTREACHED();
+    return -ENOMEM;
+  }
+}
+
+// Handle a request on the IPC channel ipc_socketpair_.
+// A request should have a file descriptor attached on which we will reply and
+// that we will then close.
+// A request should start with an int that will be used as the command type.
+bool BrokerProcess::HandleRequest() const {
+  ScopedVector<base::ScopedFD> fds;
+  char buf[kMaxMessageLength];
+  errno = 0;
+  const ssize_t msg_len = UnixDomainSocket::RecvMsg(ipc_socketpair_, buf,
+                                                    sizeof(buf), &fds);
+
+  if (msg_len == 0 || (msg_len == -1 && errno == ECONNRESET)) {
+    // EOF from our parent, or our parent died, we should die.
+    _exit(0);
+  }
+
+  // The parent should send exactly one file descriptor, on which we
+  // will write the reply.
+  // TODO(mdempsky): ScopedVector doesn't have 'at()', only 'operator[]'.
+  if (msg_len < 0 || fds.size() != 1 || fds[0]->get() < 0) {
+    PLOG(ERROR) << "Error reading message from the client";
+    return false;
+  }
+
+  base::ScopedFD temporary_ipc(fds[0]->Pass());
+
+  Pickle pickle(buf, msg_len);
+  PickleIterator iter(pickle);
+  int command_type;
+  if (pickle.ReadInt(&iter, &command_type)) {
+    bool r = false;
+    // Go through all the possible IPC messages.
+    switch (command_type) {
+      case kCommandAccess:
+      case kCommandOpen:
+        // We reply on the file descriptor sent to us via the IPC channel.
+        r = HandleRemoteCommand(static_cast<IPCCommands>(command_type),
+                                temporary_ipc.get(), pickle, iter);
+        break;
+      default:
+        NOTREACHED();
+        r = false;
+        break;
+    }
+    return r;
+  }
+
+  LOG(ERROR) << "Error parsing IPC request";
+  return false;
+}
+
+// Handle a |command_type| request contained in |read_pickle| and send the reply
+// on |reply_ipc|.
+// Currently kCommandOpen and kCommandAccess are supported.
+bool BrokerProcess::HandleRemoteCommand(IPCCommands command_type, int reply_ipc,
+                                        const Pickle& read_pickle,
+                                        PickleIterator iter) const {
+  // Currently all commands have two arguments: filename and flags.
+  std::string requested_filename;
+  int flags = 0;
+  if (!read_pickle.ReadString(&iter, &requested_filename) ||
+      !read_pickle.ReadInt(&iter, &flags)) {
+    return -1;
+  }
+
+  Pickle write_pickle;
+  std::vector<int> opened_files;
+
+  switch (command_type) {
+    case kCommandAccess:
+      AccessFileForIPC(requested_filename, flags, &write_pickle);
+      break;
+    case kCommandOpen:
+      OpenFileForIPC(requested_filename, flags, &write_pickle, &opened_files);
+      break;
+    default:
+      LOG(ERROR) << "Invalid IPC command";
+      break;
+  }
+
+  CHECK_LE(write_pickle.size(), kMaxMessageLength);
+  ssize_t sent = UnixDomainSocket::SendMsg(reply_ipc, write_pickle.data(),
+                                           write_pickle.size(), opened_files);
+
+  // Close anything we have opened in this process.
+  for (std::vector<int>::iterator it = opened_files.begin();
+       it != opened_files.end(); ++it) {
+    int ret = IGNORE_EINTR(close(*it));
+    DCHECK(!ret) << "Could not close file descriptor";
+  }
+
+  if (sent <= 0) {
+    LOG(ERROR) << "Could not send IPC reply";
+    return false;
+  }
+  return true;
+}
+
+// Perform access(2) on |requested_filename| with mode |mode| if allowed by our
+// policy. Write the syscall return value (-errno) to |write_pickle|.
+void BrokerProcess::AccessFileForIPC(const std::string& requested_filename,
+                                     int mode, Pickle* write_pickle) const {
+  DCHECK(write_pickle);
+  const char* file_to_access = NULL;
+  const bool safe_to_access_file = GetFileNameIfAllowedToAccess(
+      requested_filename.c_str(), mode, &file_to_access);
+
+  if (safe_to_access_file) {
+    CHECK(file_to_access);
+    int access_ret = access(file_to_access, mode);
+    int access_errno = errno;
+    if (!access_ret)
+      write_pickle->WriteInt(0);
+    else
+      write_pickle->WriteInt(-access_errno);
+  } else {
+    write_pickle->WriteInt(-denied_errno_);
+  }
+}
+
+// Open |requested_filename| with |flags| if allowed by our policy.
+// Write the syscall return value (-errno) to |write_pickle| and append
+// a file descriptor to |opened_files| if relevant.
+void BrokerProcess::OpenFileForIPC(const std::string& requested_filename,
+                                   int flags, Pickle* write_pickle,
+                                   std::vector<int>* opened_files) const {
+  DCHECK(write_pickle);
+  DCHECK(opened_files);
+  const char* file_to_open = NULL;
+  const bool safe_to_open_file = GetFileNameIfAllowedToOpen(
+      requested_filename.c_str(), flags, &file_to_open);
+
+  if (safe_to_open_file) {
+    CHECK(file_to_open);
+    int opened_fd = sys_open(file_to_open, flags);
+    if (opened_fd < 0) {
+      write_pickle->WriteInt(-errno);
+    } else {
+      // Success.
+      opened_files->push_back(opened_fd);
+      write_pickle->WriteInt(0);
+    }
+  } else {
+    write_pickle->WriteInt(-denied_errno_);
+  }
+}
+
+
+// Check if calling access() should be allowed on |requested_filename| with
+// mode |requested_mode|.
+// Note: access() being a system call to check permissions, this can get a bit
+// confusing. We're checking if calling access() should even be allowed with
+// the same policy we would use for open().
+// If |file_to_access| is not NULL, we will return the matching pointer from
+// the whitelist. For paranoia a caller should then use |file_to_access|. See
+// GetFileNameIfAllowedToOpen() fore more explanation.
+// return true if calling access() on this file should be allowed, false
+// otherwise.
+// Async signal safe if and only if |file_to_access| is NULL.
+bool BrokerProcess::GetFileNameIfAllowedToAccess(const char* requested_filename,
+    int requested_mode, const char** file_to_access) const {
+  // First, check if |requested_mode| is existence, ability to read or ability
+  // to write. We do not support X_OK.
+  if (requested_mode != F_OK &&
+      requested_mode & ~(R_OK | W_OK)) {
+    return false;
+  }
+  switch (requested_mode) {
+    case F_OK:
+      // We allow to check for file existence if we can either read or write.
+      return GetFileNameInWhitelist(allowed_r_files_, requested_filename,
+                                    file_to_access) ||
+             GetFileNameInWhitelist(allowed_w_files_, requested_filename,
+                                    file_to_access);
+    case R_OK:
+      return GetFileNameInWhitelist(allowed_r_files_, requested_filename,
+                                    file_to_access);
+    case W_OK:
+      return GetFileNameInWhitelist(allowed_w_files_, requested_filename,
+                                    file_to_access);
+    case R_OK | W_OK:
+    {
+      bool allowed_for_read_and_write =
+          GetFileNameInWhitelist(allowed_r_files_, requested_filename, NULL) &&
+          GetFileNameInWhitelist(allowed_w_files_, requested_filename,
+                                 file_to_access);
+      return allowed_for_read_and_write;
+    }
+    default:
+      return false;
+  }
+}
+
+// Check if |requested_filename| can be opened with flags |requested_flags|.
+// If |file_to_open| is not NULL, we will return the matching pointer from the
+// whitelist. For paranoia, a caller should then use |file_to_open| rather
+// than |requested_filename|, so that it never attempts to open an
+// attacker-controlled file name, even if an attacker managed to fool the
+// string comparison mechanism.
+// Return true if opening should be allowed, false otherwise.
+// Async signal safe if and only if |file_to_open| is NULL.
+bool BrokerProcess::GetFileNameIfAllowedToOpen(const char* requested_filename,
+    int requested_flags, const char** file_to_open) const {
+  if (!IsAllowedOpenFlags(requested_flags)) {
+    return false;
+  }
+  switch (requested_flags & O_ACCMODE) {
+    case O_RDONLY:
+      return GetFileNameInWhitelist(allowed_r_files_, requested_filename,
+                                    file_to_open);
+    case O_WRONLY:
+      return GetFileNameInWhitelist(allowed_w_files_, requested_filename,
+                                    file_to_open);
+    case O_RDWR:
+    {
+      bool allowed_for_read_and_write =
+          GetFileNameInWhitelist(allowed_r_files_, requested_filename, NULL) &&
+          GetFileNameInWhitelist(allowed_w_files_, requested_filename,
+                                 file_to_open);
+      return allowed_for_read_and_write;
+    }
+    default:
+      return false;
+  }
+}
+
+}  // namespace sandbox.