[RFC PATCH xserver v3] xwayland: Monitor client states to destroy callbacks

[Olivier Fourdan]

Client resources can survive the client itself, in which case we
may end up in our sync callback trying to access client's data after
it's been freed/reclaimed.

Add a ClientStateCallback handler to monitor the client state changes
and clear the sync callback set up by the glamor drm code if any.

Signed-off-by: Olivier Fourdan <ofourdan at redhat.com>
---
 v2: [facepalm] forgot to use the state->callback
 v3: - Rename xwlGlamorPrivateKey as xwl_auth_state_private_key getting
       rid of camelCase along the way (c'mon, this is xwayland in 2017)
     - Remove test for clientGone in the sync callback and add a comment
       as to why this is not needed anymore
     - Fix GNOME-style-coding space between parenthesis
     - Register private key before the callback in xwl_glamor_init() so
       that we don't need to delete the callback if the register fails.
     

 hw/xwayland/xwayland-glamor.c | 59 ++++++++++++++++++++++++++++++++++++-------
 1 file changed, 50 insertions(+), 9 deletions(-)

diff --git a/hw/xwayland/xwayland-glamor.c b/hw/xwayland/xwayland-glamor.c
index 65c3c00..63f2303 100644
--- a/hw/xwayland/xwayland-glamor.c
+++ b/hw/xwayland/xwayland-glamor.c
@@ -38,6 +38,8 @@
 #include <dri3.h>
 #include "drm-client-protocol.h"
 
+static DevPrivateKeyRec xwl_auth_state_private_key;
+
 struct xwl_pixmap {
     struct wl_buffer *buffer;
     struct gbm_bo *bo;
@@ -429,20 +431,49 @@ glamor_egl_dri3_fd_name_from_tex(ScreenPtr screen,
 struct xwl_auth_state {
     int fd;
     ClientPtr client;
+    struct wl_callback *callback;
 };
 
 static void
+free_xwl_auth_state(ClientPtr pClient, struct xwl_auth_state *state)
+{
+    dixSetPrivate(&pClient->devPrivates, &xwl_auth_state_private_key, NULL);
+    if (state) {
+        wl_callback_destroy(state->callback);
+        free(state);
+    }
+}
+
+static void
+xwl_auth_state_client_callback(CallbackListPtr *pcbl, void *unused, void *data)
+{
+    NewClientInfoRec *clientinfo = (NewClientInfoRec *) data;
+    ClientPtr pClient = clientinfo->client;
+    struct xwl_auth_state *state;
+
+    switch (pClient->clientState) {
+    case ClientStateGone:
+    case ClientStateRetained:
+        state = dixLookupPrivate(&pClient->devPrivates, &xwl_auth_state_private_key);
+        free_xwl_auth_state(pClient, state);
+        break;
+    default:
+        break;
+    }
+}
+
+static void
 sync_callback(void *data, struct wl_callback *callback, uint32_t serial)
 {
     struct xwl_auth_state *state = data;
     ClientPtr client = state->client;
 
-    if (!client->clientGone) {
-        dri3_send_open_reply(client, state->fd);
-        AttendClient(client);
-    }
-    free(state);
-    wl_callback_destroy(callback);
+    /* if the client is gone, the callback is cancelled so it's safe to
+     * assume the client is still in ClientStateRunning at this point...
+     */
+    dri3_send_open_reply(client, state->fd);
+    AttendClient(client);
+    free_xwl_auth_state(client, state);
 }
 
 static const struct wl_callback_listener sync_listener = {
@@ -457,7 +488,6 @@ xwl_dri3_open_client(ClientPtr client,
 {
     struct xwl_screen *xwl_screen = xwl_screen_get(screen);
     struct xwl_auth_state *state;
-    struct wl_callback *callback;
     drm_magic_t magic;
     int fd;
 
@@ -485,8 +515,9 @@ xwl_dri3_open_client(ClientPtr client,
     }
 
     wl_drm_authenticate(xwl_screen->drm, magic);
-    callback = wl_display_sync(xwl_screen->display);
-    wl_callback_add_listener(callback, &sync_listener, state);
+    state->callback = wl_display_sync(xwl_screen->display);
+    wl_callback_add_listener(state->callback, &sync_listener, state);
+    dixSetPrivate(&client->devPrivates, &xwl_auth_state_private_key, state);
 
     IgnoreClient(client);
 
@@ -568,6 +599,16 @@ xwl_glamor_init(struct xwl_screen *xwl_screen)
         return FALSE;
     }
 
+    if (!dixRegisterPrivateKey(&xwl_auth_state_private_key, PRIVATE_CLIENT, 0)) {
+        ErrorF("Failed to register private key\n");
+        return FALSE;
+    }
+
+    if (!AddCallback(&ClientStateCallback, xwl_auth_state_client_callback, NULL)) {
+        ErrorF("Failed to add client state callback\n");
+        return FALSE;
+    }
+
     xwl_screen->CreateScreenResources = screen->CreateScreenResources;
     screen->CreateScreenResources = xwl_glamor_create_screen_resources;
     screen->CreatePixmap = xwl_glamor_create_pixmap;
-- 
2.9.3