[Spice-devel] [PATCH spice 1/5] spicec: Move setting of clipboard_owner to guest to platform code

[Hans de Goede]

Atleast under x11 there is a race condition when setting the clipboard
owner to guest from the RedClient code rather then doing it in Platform.

After the XSetSelectionOwner() in Platform::on_clipboard_grab(), which runs
from the main message loop thread, the x11 event thread can receive a
SelectionRequest event from another x11 app, before the RedClient code
has set the clipboard owner, which will trigger the owner != guest
check in the SelectionRequest event handling code.

By moving the setting of the owner in to Platform::on_clipboard_grab() it
gets protected by the clipboard lock, which closes this tiny race.
---
 client/platform.h           |    2 ++
 client/red_client.cpp       |    1 -
 client/windows/platform.cpp |    7 +++++++
 client/x11/platform.cpp     |   10 ++++++++--
 4 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/client/platform.h b/client/platform.h
index af4a0f6..a9a1715 100644
--- a/client/platform.h
+++ b/client/platform.h
@@ -132,6 +132,8 @@ public:
     static int  get_clipboard_owner() { return _clipboard_owner; }
 
 private:
+    static void set_clipboard_owner_unlocked(int new_owner);
+
     static int _clipboard_owner;
 };
 
diff --git a/client/red_client.cpp b/client/red_client.cpp
index 8e7dfe0..0650e35 100644
--- a/client/red_client.cpp
+++ b/client/red_client.cpp
@@ -1118,7 +1118,6 @@ void RedClient::dispatch_agent_message(VDAgentMessage* msg, void* data)
     case VD_AGENT_CLIPBOARD_GRAB:
         Platform::on_clipboard_grab((uint32_t *)data,
                                       msg->size / sizeof(uint32_t));
-        Platform::set_clipboard_owner(Platform::owner_guest);
         break;
     case VD_AGENT_CLIPBOARD_REQUEST:
         if (Platform::get_clipboard_owner() != Platform::owner_client) {
diff --git a/client/windows/platform.cpp b/client/windows/platform.cpp
index 580a40a..075d269 100644
--- a/client/windows/platform.cpp
+++ b/client/windows/platform.cpp
@@ -859,6 +859,11 @@ void WinPlatform::exit_modal_loop()
 
 int Platform::_clipboard_owner = Platform::owner_none;
 
+void Platform::set_clipboard_owner_unlocked(int new_owner)
+{
+    set_clipboard_owner(new_owner);
+}
+
 void Platform::set_clipboard_owner(int new_owner)
 {
     if (new_owner == owner_none) {
@@ -885,6 +890,8 @@ bool Platform::on_clipboard_grab(uint32_t *types, uint32_t type_count)
     EmptyClipboard();
     SetClipboardData(format, NULL);
     CloseClipboard();
+
+    set_clipboard_owner(owner_guest);
     return true;
 }
 
diff --git a/client/x11/platform.cpp b/client/x11/platform.cpp
index 29b5f75..8f0665c 100644
--- a/client/x11/platform.cpp
+++ b/client/x11/platform.cpp
@@ -3355,6 +3355,8 @@ bool Platform::on_clipboard_grab(uint32_t *types, uint32_t type_count)
 
     XSetSelectionOwner(x_display, clipboard_prop, platform_win, CurrentTime);
     XFlush(x_display);
+
+    set_clipboard_owner_unlocked(owner_guest);
     return true;
 }
 
@@ -3362,12 +3364,16 @@ int Platform::_clipboard_owner = Platform::owner_none;
 
 void Platform::set_clipboard_owner(int new_owner)
 {
+        Lock lock(clipboard_lock);
+        set_clipboard_owner_unlocked(new_owner);
+}
+
+void Platform::set_clipboard_owner_unlocked(int new_owner)
+{
     const char * const owner_str[] = { "none", "guest", "client" };
 
     /* Clear pending requests and clipboard data */
     {
-        Lock lock(clipboard_lock);
-
         if (next_selection_request) {
             LOG_INFO("selection requests pending upon clipboard owner change, clearing");
             while (next_selection_request)
-- 
1.7.2.2