Run container as unprivileged for enhanced security

On the Android side this requires no change with the current setup.

src/anbox/container/lxc_container.cpp

@@ -35,7 +35,8 @@ namespace fs = boost::filesystem;
 
 namespace anbox {
 namespace container {
-LxcContainer::LxcContainer() : state_(State::inactive), container_(nullptr) {
+LxcContainer::LxcContainer(const network::Credentials &creds)
+    : state_(State::inactive), container_(nullptr), creds_(creds) {
   utils::ensure_paths({
       config::container_config_path(), config::log_path(),
   });
@@ -49,6 +50,32 @@ LxcContainer::~LxcContainer() {
   if (container_) lxc_container_put(container_);
 }
 
+void LxcContainer::setup_id_maps() {
+  const auto base_id = 100000;
+  const auto max_id = 65536;
+  set_config_item("lxc.id_map",
+                  utils::string_format("u 0 %d %d", base_id, creds_.uid() - 1));
+  set_config_item("lxc.id_map",
+                  utils::string_format("g 0 %d %d", base_id, creds_.gid() - 1));
+
+  // We need to bind the user id for the one running the client side
+  // process as he is the owner of various socket files we bind mount
+  // into the container.
+  set_config_item("lxc.id_map",
+                  utils::string_format("u %d %d 1", creds_.uid(), creds_.uid()));
+  set_config_item("lxc.id_map",
+                  utils::string_format("g %d %d 1", creds_.gid(), creds_.gid()));
+
+  set_config_item("lxc.id_map",
+                  utils::string_format("u %d %d %d", creds_.uid() + 1,
+                                       base_id + creds_.uid() + 1,
+                                       max_id - creds_.uid() - 1));
+  set_config_item("lxc.id_map",
+                  utils::string_format("g %d %d %d", creds_.uid() + 1,
+                                       base_id + creds_.gid() + 1,
+                                       max_id - creds_.gid() - 1));
+}
+
 void LxcContainer::start(const Configuration &configuration) {
   if (getuid() != 0)
     BOOST_THROW_EXCEPTION(
@@ -128,7 +155,20 @@ void LxcContainer::start(const Configuration &configuration) {
   set_config_item("lxc.aa_profile", "unconfined");
 #endif
 
-  for (const auto &bind_mount : configuration.bind_mounts) {
+  setup_id_maps();
+
+  auto bind_mounts = configuration.bind_mounts;
+
+  // Extra bind-mounts for user-namespace setup
+  bind_mounts.insert({"/dev/console", "dev/console"});
+  bind_mounts.insert({"/dev/full", "dev/full"});
+  bind_mounts.insert({"/dev/null", "dev/null"});
+  bind_mounts.insert({"/dev/random", "dev/random"});
+  bind_mounts.insert({"/dev/tty", "dev/tty"});
+  bind_mounts.insert({"/dev/urandom", "dev/urandom"});
+  bind_mounts.insert({"/dev/zero", "dev/zero"});
+
+  for (const auto &bind_mount : bind_mounts) {
     std::string create_type = "file";
 
     if (fs::is_directory(bind_mount.first)) create_type = "dir";

src/anbox/container/lxc_container.h

@@ -19,6 +19,7 @@
 #define ANBOX_CONTAINER_LXC_CONTAINER_H_
 
 #include "anbox/container/container.h"
+#include "anbox/network/credentials.h"
 
 #include <string>
 
@@ -28,7 +29,7 @@ namespace anbox {
 namespace container {
 class LxcContainer : public Container {
  public:
-  LxcContainer();
+  LxcContainer(const network::Credentials &creds);
   ~LxcContainer();
 
   void start(const Configuration &configuration) override;
@@ -37,9 +38,11 @@ class LxcContainer : public Container {
 
  private:
   void set_config_item(const std::string &key, const std::string &value);
+  void setup_id_maps();
 
   State state_;
   lxc_container *container_;
+  network::Credentials creds_;
 };
 }  // namespace container
 }  // namespace anbox

src/anbox/container/management_api_skeleton.cpp

@@ -59,8 +59,6 @@ void ManagementApiSkeleton::start_container(
         utils::string_format("Failed to start container: %s", err.what()));
   }
 
-  DEBUG("");
-
   done->Run();
 }
 }  // namespace container

src/anbox/container/service.cpp

@@ -77,7 +77,7 @@ void Service::new_client(
   auto pending_calls = std::make_shared<rpc::PendingCallCache>();
   auto rpc_channel = std::make_shared<rpc::Channel>(pending_calls, messenger);
   auto server = std::make_shared<container::ManagementApiSkeleton>(
-      pending_calls, std::make_shared<LxcContainer>());
+      pending_calls, std::make_shared<LxcContainer>(messenger->creds()));
   auto processor = std::make_shared<container::ManagementApiMessageProcessor>(
       messenger, pending_calls, server);