[PATCH 05/19] qxl_surface: handle destroyed pixmaps while evacuated

[Alon Levy]

Prevent access to freed memory when:
1. qxl_leave_vt/qxl_surface_cache_evacuate_all freed cache->all_surfaces
2. ProcRenderDispatch/damageDestroyPixmap/qxl_destroy_pixmap/qxl_surface_kill
access a surface that pointed inside the all_surfaces array

Solution in this patch:
1. never free all_surfaces
2. add an 'evacuated' field per surface, initialied to NULL, set during
evacuation.
3. on qxl_surface_kill, if surface->evacuated is set, don't destroy the
surface (it is already destroyed by this point via a reset in
qxl_surface_cache_evacuate_all's caller, qxl_leave_vt), just unref the
host pixmap, free the evacuated_surface_t and unlink it from the
evacuated linked list, so it isn't recreated later on
qxl_surface_cache_replace_all.
---
 src/qxl_surface.c |   44 +++++++++++++++++++++++++++++++++++++-------
 1 file changed, 37 insertions(+), 7 deletions(-)

diff --git a/src/qxl_surface.c b/src/qxl_surface.c
index cb0de1d..d999b4d 100644
--- a/src/qxl_surface.c
+++ b/src/qxl_surface.c
@@ -76,7 +76,9 @@ struct qxl_surface_t
     int			ref_count;
 
     PixmapPtr		pixmap;
-    
+
+    struct evacuated_surface_t *evacuated;
+
     union
     {
 	qxl_surface_t *copy_src;
@@ -90,6 +92,7 @@ struct evacuated_surface_t
     PixmapPtr		 pixmap;
     int			 bpp;
 
+    evacuated_surface_t *prev;
     evacuated_surface_t *next;
 };
 
@@ -125,9 +128,14 @@ surface_cache_init (surface_cache_t *cache, qxl_screen_t *qxl)
     int n_surfaces = qxl->rom->n_surfaces;
     int i;
 
-    cache->all_surfaces = calloc (n_surfaces, sizeof (qxl_surface_t));
-    if (!cache->all_surfaces)
-	return FALSE;
+    if (!cache->all_surfaces) {
+        /* all_surfaces is not freed when evacuating, since surfaces are still
+         * tied to pixmaps that may be destroyed after evacuation before
+         * recreation */
+        cache->all_surfaces = calloc (n_surfaces, sizeof (qxl_surface_t));
+        if (!cache->all_surfaces)
+            return FALSE;
+    }
 
     memset (cache->all_surfaces, 0, n_surfaces * sizeof (qxl_surface_t));
     memset (cache->cached_surfaces, 0, N_CACHED_SURFACES * sizeof (qxl_surface_t *));
@@ -141,6 +149,7 @@ surface_cache_init (surface_cache_t *cache, qxl_screen_t *qxl)
 	cache->all_surfaces[i].cache = cache;
 	cache->all_surfaces[i].dev_image = NULL;
 	cache->all_surfaces[i].host_image = NULL;
+	cache->all_surfaces[i].evacuated = NULL;
 	
 	REGION_INIT (
 	    NULL, &(cache->all_surfaces[i].access_region), (BoxPtr)NULL, 0);
@@ -165,6 +174,7 @@ qxl_surface_cache_create (qxl_screen_t *qxl)
     if (!cache)
 	return NULL;
 
+    memset(cache, 0, sizeof(*cache));
     cache->qxl = qxl;
     if (!surface_cache_init (cache, qxl))
     {
@@ -344,6 +354,7 @@ qxl_surface_cache_create_primary (surface_cache_t	*cache,
     surface->bpp = mode->bits;
     surface->next = NULL;
     surface->prev = NULL;
+    surface->evacuated = NULL;
     
     REGION_INIT (NULL, &(surface->access_region), (BoxPtr)NULL, 0);
     surface->access_type = UXA_ACCESS_RO;
@@ -790,6 +801,23 @@ qxl_surface_unref (surface_cache_t *cache, uint32_t id)
 void
 qxl_surface_kill (qxl_surface_t *surface)
 {
+    struct evacuated_surface_t *ev = surface->evacuated;
+
+    if (ev) {
+        /* server side surface is already destroyed (via reset), don't
+         * resend a destroy. Just mark surface as not to be recreated */
+        ev->pixmap = NULL;
+        if (ev->image)
+            pixman_image_unref (ev->image);
+        if (ev->next)
+            ev->next->prev = ev->prev;
+        if (ev->prev)
+            ev->prev->next = ev->next;
+        free(ev);
+        surface->evacuated = NULL;
+        return;
+    }
+
     unlink_surface (surface);
 
     if (surface->id != 0					&&
@@ -1041,16 +1069,18 @@ qxl_surface_cache_evacuate_all (surface_cache_t *cache)
 	unlink_surface (s);
 	
 	evacuated->next = evacuated_surfaces;
+        if (evacuated_surfaces) {
+            evacuated_surfaces->prev = evacuated;
+        }
 	evacuated_surfaces = evacuated;
+        s->evacuated = evacuated;
 
 	s = next;
     }
 
-    free (cache->all_surfaces);
-    cache->all_surfaces = NULL;
     cache->live_surfaces = NULL;
     cache->free_surfaces = NULL;
-    
+
     return evacuated_surfaces;
 }
 
-- 
1.7.10.1