mir/agent: fix indefinite wait if fail to start prompt session

src/core/trust/mir/agent.cpp

@@ -56,6 +56,11 @@ mir::PromptSessionVirtualTable::PromptSessionVirtualTable()
 {
 }
 
+std::string mir::PromptSessionVirtualTable::error_message()
+{
+    return std::string(mir_prompt_session_error_message(prompt_session));
+}
+
 int mir::PromptSessionVirtualTable::new_fd_for_prompt_provider()
 {
     static const unsigned int fd_count = 1;
@@ -241,10 +246,19 @@ core::trust::Request::Answer mir::Agent::authenticate_request_with_parameters(co
                     parameters.application.pid,
                     Agent::on_trust_session_changed_state,
                     &cb_context),
-        // Acquire a new fd for the prompt provider.
-        scope.prompt_session->new_fd_for_prompt_provider()
+        /* fd */ -1
     };
 
+    auto error = scope.prompt_session->error_message();
+    if (!error.empty()) {
+        throw std::runtime_error{
+            "Unable to create a prompt session: " + error
+        };
+    }
+
+    // Acquire a new fd for the prompt provider.
+    scope.fd = scope.prompt_session->new_fd_for_prompt_provider();
+
     // And prepare the actual execution in a child process.
     mir::PromptProviderHelper::InvocationArguments args
     {

src/core/trust/mir/agent.h

@@ -64,6 +64,9 @@ class CORE_TRUST_DLL_PUBLIC PromptSessionVirtualTable
     PromptSessionVirtualTable(MirPromptSession* prompt_session);
     virtual ~PromptSessionVirtualTable() = default;
 
+    // Retrieve a text description of the last error.
+    virtual std::string error_message();
+
     // Requests a new, pre-authenticated fd for associating prompt providers.
     // Returns the fd or throws std::runtime_error.
     virtual int new_fd_for_prompt_provider();

tests/mir_agent_test.cpp

@@ -42,6 +42,9 @@ struct MockPromptSessionVirtualTable : public core::trust::mir::PromptSessionVir
     {
     }
 
+    // Retrieve a text description of the last error.
+    MOCK_METHOD0(error_message, std::string());
+
     // Requests a new, pre-authenticated fd for associating prompt providers.
     // Returns the fd or throws std::runtime_error.
     MOCK_METHOD0(new_fd_for_prompt_provider, int());
@@ -234,6 +237,9 @@ TEST(MirAgent, creates_prompt_session_and_execs_helper_with_preauthenticated_fd)
     ON_CALL(*connection_vtable, create_prompt_session_sync(_, _, _))
             .WillByDefault(Return(prompt_session_vtable));
 
+    ON_CALL(*prompt_session_vtable, error_message())
+            .WillByDefault(Return(std::string()));
+
     ON_CALL(*prompt_session_vtable, new_fd_for_prompt_provider())
             .WillByDefault(Return(pre_authenticated_fd));
 
@@ -305,6 +311,9 @@ TEST(MirAgent, calls_into_app_info_resolver_with_app_id)
     ON_CALL(*connection_vtable, create_prompt_session_sync(_, _, _))
             .WillByDefault(Return(prompt_session_vtable));
 
+    ON_CALL(*prompt_session_vtable, error_message())
+            .WillByDefault(Return(std::string()));
+
     ON_CALL(*prompt_session_vtable, new_fd_for_prompt_provider())
             .WillByDefault(Return(pre_authenticated_fd));
 
@@ -380,6 +389,9 @@ TEST(MirAgent, sig_kills_prompt_provider_process_on_status_change)
                         a_spinning_process,
                         core::posix::StandardStream::empty)));
 
+    ON_CALL(*prompt_session_vtable, error_message())
+            .WillByDefault(Return(std::string()));
+
     ON_CALL(*prompt_session_vtable, new_fd_for_prompt_provider())
             .WillByDefault(
                 Return(
@@ -445,6 +457,65 @@ TEST(MirAgent, sig_kills_prompt_provider_process_on_status_change)
         asynchronously_stop_the_prompting_session.join();
 }
 
+TEST(MirAgent, dont_exec_provider_when_unable_to_create_a_prompt_session)
+{
+    using namespace ::testing;
+
+    const core::trust::Pid app_pid {21};
+    const std::string app_icon{"/tmp"};
+    const std::string app_name {"Does not exist"};
+    const std::string app_id {"does.not.exist.application"};
+    const core::trust::Feature feature{42};
+    const std::string app_description {"This is just an extended description %1%"};
+    const int pre_authenticated_fd {42};
+
+    auto connection_vtable = a_mocked_connection_vtable();
+    auto prompt_session_vtable = a_mocked_prompt_session_vtable();
+
+    auto prompt_provider_exec_helper = a_mocked_prompt_provider_calling_bin_false();
+    auto app_info_resolver = a_mocked_app_info_resolver();
+
+    ON_CALL(*connection_vtable, create_prompt_session_sync(_, _, _))
+            .WillByDefault(Return(prompt_session_vtable));
+
+    ON_CALL(*prompt_session_vtable, error_message())
+            .WillByDefault(Return(std::string("Fabricated error.")));
+    ON_CALL(*prompt_session_vtable, new_fd_for_prompt_provider())
+            .WillByDefault(Return(pre_authenticated_fd));
+
+    ON_CALL(*app_info_resolver, resolve(_))
+            .WillByDefault(Return(core::trust::mir::AppInfo{app_icon, app_name, app_id}));
+
+    EXPECT_CALL(*connection_vtable, create_prompt_session_sync(app_pid, _, _)).Times(1);
+    EXPECT_CALL(*prompt_session_vtable, error_message()).Times(1);
+    // We have an error. New FD shouldn't be requested, and the prompt provider
+    // shouldn't be exec'ed, otherwise the provider can hang.
+    EXPECT_CALL(*prompt_session_vtable, new_fd_for_prompt_provider()).Times(0);
+    EXPECT_CALL(*prompt_provider_exec_helper,
+                exec_prompt_provider_with_arguments(_)).Times(0);
+
+    core::trust::mir::Agent agent
+    {
+        core::trust::mir::Agent::Configuration
+        {
+            connection_vtable,
+            prompt_provider_exec_helper,
+            core::trust::mir::Agent::translator_only_accepting_exit_status_success(),
+            app_info_resolver
+        }
+    };
+
+    EXPECT_THROW(agent.authenticate_request_with_parameters(
+                  core::trust::Agent::RequestParameters
+                  {
+                     core::trust::Uid{::getuid()},
+                     app_pid,
+                     app_id,
+                     feature,
+                     app_description
+                  }), std::runtime_error);
+}
+
 TEST(TrustPrompt, aborts_for_missing_title)
 {
     // And we pass in an empty argument vector