Initial implementation of the Mac Bootstrap Sandbox.

sandbox/mac/launchd_interception_server.cc

+// Copyright 2014 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/mac/launchd_interception_server.h"
+
+#include <bsm/libbsm.h>
+#include <servers/bootstrap.h>
+
+#include "base/logging.h"
+#include "base/mac/mach_logging.h"
+#include "sandbox/mac/bootstrap_sandbox.h"
+
+namespace sandbox {
+
+// The buffer size for all launchd messages. This comes from
+// sizeof(union __RequestUnion__vproc_mig_job_subsystem) in launchd, and it
+// is larger than the __ReplyUnion.
+const mach_msg_size_t kBufferSize = mach_vm_round_page(2096 +
+    sizeof(mach_msg_audit_trailer_t));
+
+LaunchdInterceptionServer::LaunchdInterceptionServer(
+    const BootstrapSandbox* sandbox)
+    : sandbox_(sandbox),
+      server_port_(MACH_PORT_NULL),
+      server_queue_(NULL),
+      server_source_(NULL),
+      sandbox_port_(MACH_PORT_NULL),
+      compat_shim_(GetLaunchdCompatibilityShim()) {
+}
+
+LaunchdInterceptionServer::~LaunchdInterceptionServer() {
+  if (server_source_)

[Mark Mentovai, 2014/05/09 22:34:23]

Good call. The source code shows that dispatch_release doesn’t NULL-check, so
this is necessary.

The compiler had no way to know whether you were doing anything dangerous.

+    dispatch_release(server_source_);
+  if (server_queue_)
+    dispatch_release(server_queue_);
+}
+
+bool LaunchdInterceptionServer::Initialize() {
+  mach_port_t task = mach_task_self();
+  kern_return_t kr;
+
+  // Allocate a port for use as a new bootstrap port.
+  mach_port_t port;
+  if ((kr = mach_port_allocate(task, MACH_PORT_RIGHT_RECEIVE, &port)) !=
+          KERN_SUCCESS) {
+    MACH_LOG(ERROR, kr) << "Failed to allocate new bootstrap port.";
+    return false;
+  }
+  if ((kr = mach_port_insert_right(task, port, port, MACH_MSG_TYPE_MAKE_SEND))
+          != KERN_SUCCESS) {
+    MACH_LOG(ERROR, kr) << "Failed to insert send right on bootstrap port.";
+    return false;
+  }
+  server_port_.reset(port);
+
+  // Allocate the message request and reply buffers.
+  const int kMachMsgMemoryFlags = VM_MAKE_TAG(VM_MEMORY_MACH_MSG) |
+                                  VM_FLAGS_ANYWHERE;
+  vm_address_t buffer = 0;
+
+  kr = vm_allocate(task, &buffer, kBufferSize, kMachMsgMemoryFlags);
+  if (kr != KERN_SUCCESS) {
+    MACH_LOG(ERROR, kr) << "Failed to allocate request buffer.";
+    return false;
+  }
+  request_buffer_.reset(buffer, kBufferSize);
+
+  kr = vm_allocate(task, &buffer, kBufferSize, kMachMsgMemoryFlags);
+  if (kr != KERN_SUCCESS) {
+    MACH_LOG(ERROR, kr) << "Failed to allocate reply buffer.";
+    return false;
+  }
+  reply_buffer_.reset(buffer, kBufferSize);
+
+  // Allocate the dummy sandbox port.
+  if ((kr = mach_port_allocate(task, MACH_PORT_RIGHT_RECEIVE, &port)) !=
+          KERN_SUCCESS) {
+    MACH_LOG(ERROR, kr) << "Failed to allocate dummy sandbox port.";
+    return false;
+  }
+  sandbox_port_.reset(port);
+
+  // Set up the dispatch queue to service the bootstrap port.
+  // TODO(rsesek): Specify DISPATCH_QUEUE_SERIAL, in the 10.7 SDK. NULL means
+  // the same thing but is not symbolically clear.
+  server_queue_ = dispatch_queue_create(
+      "org.chromium.sandbox.LaunchdInterceptionServer", NULL);
+  server_source_ = dispatch_source_create(DISPATCH_SOURCE_TYPE_MACH_RECV,
+      server_port_.get(), 0, server_queue_);
+  dispatch_source_set_event_handler(server_source_, ^{ ReceiveMessage(); });
+  dispatch_resume(server_source_);
+
+  return true;
+}
+
+void LaunchdInterceptionServer::ReceiveMessage() {
+  const mach_msg_options_t kRcvOptions = MACH_RCV_MSG |
+      MACH_RCV_TRAILER_TYPE(MACH_MSG_TRAILER_FORMAT_0) |
+      MACH_RCV_TRAILER_ELEMENTS(MACH_RCV_TRAILER_AUDIT);
+
+  mach_msg_header_t* request =
+      reinterpret_cast<mach_msg_header_t*>(request_buffer_.address());
+  mach_msg_header_t* reply =
+      reinterpret_cast<mach_msg_header_t*>(reply_buffer_.address());
+
+  // Zero out the buffers from handling any previous message.
+  bzero(request, kBufferSize);
+  bzero(reply, kBufferSize);
+
+  // A Mach message server-once. The system library to run a message server
+  // cannot be used here, because some requests are conditionally forwarded
+  // to another server.
+  kern_return_t kr = mach_msg(request, kRcvOptions, 0, kBufferSize,
+      server_port_.get(), MACH_MSG_TIMEOUT_NONE, MACH_PORT_NULL);
+  if (kr != KERN_SUCCESS) {
+    MACH_LOG(ERROR, kr) << "Unable to receive message.";
+    return;
+  }
+
+  // Set up a reply message in case it will be used.
+  reply->msgh_bits = MACH_MSGH_BITS_REMOTE(reply->msgh_bits);
+  // Since mach_msg will automatically swap the request and reply ports,
+  // undo that.
+  reply->msgh_remote_port = request->msgh_remote_port;
+  reply->msgh_local_port = MACH_PORT_NULL;
+  // MIG servers simply add 100 to the request ID to generate the reply ID.
+  reply->msgh_id = request->msgh_id + 100;
+
+  // Process the message.
+  DemuxMessage(request, reply);
+
+  // Free any descriptors in the message body.
+  mach_msg_destroy(request);
+  mach_msg_destroy(reply);
+}
+
+void LaunchdInterceptionServer::DemuxMessage(mach_msg_header_t* request,
+                                             mach_msg_header_t* reply) {
+  VLOG(3) << "Incoming message #" << request->msgh_id;
+
+  // Get the PID of the task that sent this request. This requires getting at
+  // the trailer of the message, from the header.
+  mach_msg_audit_trailer_t* trailer =
+      reinterpret_cast<mach_msg_audit_trailer_t*>(
+          reinterpret_cast<vm_address_t>(request) +
+              round_msg(request->msgh_size));
+  // TODO(rsesek): In the 10.7 SDK, there's audit_token_to_pid().
+  pid_t sender_pid;
+  audit_token_to_au32(trailer->msgh_audit,
+      NULL, NULL, NULL, NULL, NULL, &sender_pid, NULL, NULL);
+
+  if (sandbox_->PolicyForProcess(sender_pid) == NULL) {
+    // No sandbox policy is in place for the sender of this message, which
+    // means it is from the sandbox host process or an unsandboxed child.
+    VLOG(3) << "Message from pid " << sender_pid << " forwarded to launchd";
+    ForwardMessage(request, reply);
+    return;
+  }
+
+  if (request->msgh_id == compat_shim_.msg_id_look_up2) {
+    // Filter messages sent via bootstrap_look_up to enforce the sandbox policy
+    // over the bootstrap namespace.
+    HandleLookUp(request, reply, sender_pid);
+  } else if (request->msgh_id == compat_shim_.msg_id_swap_integer) {
+    // Ensure that any vproc_swap_integer requests are safe.
+    HandleSwapInteger(request, reply, sender_pid);
+  } else {
+    // All other messages are not permitted.
+    VLOG(1) << "Rejecting unhandled message #" << request->msgh_id;
+    RejectMessage(request, reply, MIG_REMOTE_ERROR);
+  }
+}
+
+void LaunchdInterceptionServer::HandleLookUp(mach_msg_header_t* request,
+                                             mach_msg_header_t* reply,
+                                             pid_t sender_pid) {
+  const std::string request_service_name(
+      compat_shim_.look_up2_get_request_name(request));
+  VLOG(2) << "Incoming look_up2 request for " << request_service_name;
+
+  // Find the Rule for this service. If one is not found, use
+  // a safe default, POLICY_DENY_ERROR.
+  const BootstrapSandboxPolicy* policy = sandbox_->PolicyForProcess(sender_pid);
+  const BootstrapSandboxPolicy::const_iterator it =
+      policy->find(request_service_name);
+  Rule rule(POLICY_DENY_ERROR);
+  if (it != policy->end())
+    rule = it->second;
+
+  if (rule.result == POLICY_ALLOW) {
+    // This service is explicitly allowed, so this message will not be
+    // intercepted by the sandbox.
+    VLOG(1) << "Permitting and forwarding look_up2: " << request_service_name;
+    ForwardMessage(request, reply);
+  } else if (rule.result == POLICY_DENY_ERROR) {
+    // The child is not permitted to look up this service. Send a MIG error
+    // reply to the client. Returning a NULL or unserviced port for a look up
+    // can cause clients to crash or hang.
+    VLOG(1) << "Denying look_up2 with MIG error: " << request_service_name;
+    RejectMessage(request, reply, BOOTSTRAP_UNKNOWN_SERVICE);
+  } else if (rule.result == POLICY_DENY_DUMMY_PORT ||
+             rule.result == POLICY_SUBSTITUTE_PORT) {
+    // The policy result is to deny access to the real service port, replying
+    // with a sandboxed port in its stead. Use either the dummy sandbox_port_
+    // or the one specified in the policy.
+    VLOG(1) << "Intercepting look_up2 with a sandboxed service port: "
+            << request_service_name;
+
+    mach_port_t result_port;
+    if (rule.result == POLICY_DENY_DUMMY_PORT)
+      result_port = sandbox_port_.get();
+    else
+      result_port = rule.substitute_port;
+
+    // Grant an additional send right on the result_port so that it can be
+    // sent to the sandboxed child process.
+    kern_return_t kr = mach_port_insert_right(mach_task_self(),
+        result_port, result_port, MACH_MSG_TYPE_MAKE_SEND);
+    if (kr != KERN_SUCCESS) {
+      MACH_LOG(ERROR, kr) << "Unable to insert right on result_port.";
+    }
+
+    compat_shim_.look_up2_fill_reply(reply, result_port);
+    SendReply(reply);
+  } else {
+    NOTREACHED();
+  }
+}
+
+void LaunchdInterceptionServer::HandleSwapInteger(mach_msg_header_t* request,
+                                                  mach_msg_header_t* reply,
+                                                  pid_t sender_pid) {
+  // TODO(rsesek): Crack the message and ensure that the swap is only being
+  // used to get the value of a VPROC key, and do not allow setting it.
+  VLOG(2) << "Forwarding vproc swap message #" << request->msgh_id;
+  ForwardMessage(request, reply);
+}
+
+void LaunchdInterceptionServer::SendReply(mach_msg_header_t* reply) {
+  kern_return_t kr = mach_msg(reply, MACH_SEND_MSG, reply->msgh_size, 0,
+      MACH_PORT_NULL, MACH_MSG_TIMEOUT_NONE, MACH_PORT_NULL);
+  if (kr != KERN_SUCCESS) {
+    MACH_LOG(ERROR, kr) << "Unable to send intercepted reply message.";
+  }
+}
+
+void LaunchdInterceptionServer::ForwardMessage(mach_msg_header_t* request,
+                                               mach_msg_header_t* reply) {
+  request->msgh_local_port = request->msgh_remote_port;
+  request->msgh_remote_port = sandbox_->real_bootstrap_port();
+  // Preserve the msgh_bits that do not deal with the local and remote ports.
+  request->msgh_bits = (request->msgh_bits & ~MACH_MSGH_BITS_PORTS_MASK) |
+      MACH_MSGH_BITS(MACH_MSG_TYPE_COPY_SEND, MACH_MSG_TYPE_MOVE_SEND_ONCE);
+  kern_return_t kr = mach_msg_send(request);
+  if (kr != KERN_SUCCESS) {
+    MACH_LOG(ERROR, kr) << "Unable to forward message to the real launchd.";
+  }
+}
+
+void LaunchdInterceptionServer::RejectMessage(mach_msg_header_t* request,
+                                              mach_msg_header_t* reply,
+                                              int error_code) {
+  mig_reply_error_t* error_reply = reinterpret_cast<mig_reply_error_t*>(reply);
+  error_reply->Head.msgh_size = sizeof(mig_reply_error_t);
+  error_reply->Head.msgh_bits =
+      MACH_MSGH_BITS_REMOTE(MACH_MSG_TYPE_MOVE_SEND_ONCE);
+  error_reply->NDR = NDR_record;
+  error_reply->RetCode = error_code;
+  SendReply(&error_reply->Head);
+}
+
+}  // namespace sandbox