Xen devel - Nov 2007 - [PATCH 0/2][PVFB][TOOLS] Bogus screen updates

The PVFB frontend can get confused and send a bogus screen update to the back
end when the screen is clean.

Two parts: fix the frontend not to do that, and fix the backend not to
choke on it.

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The PVFB frontend can get confused and send a screen update to the
backend when the screen is actually clean.  Such an update asks for
the impossible rectangle (x1, x2, y1, y2) = (INT_MAX, 0, INT_MAX, 0).
Fix by setting the dirty flag in the obvious place: when the dirty
rectangle is grown.

Signed-off-by: Markus Armbruster <armbru@redhat.com>

diff -r cf8b6cafa2f0 drivers/xen/fbfront/xenfb.c
--- a/drivers/xen/fbfront/xenfb.c	Thu Nov 08 18:26:08 2007 +0000
+++ b/drivers/xen/fbfront/xenfb.c	Tue Nov 13 17:32:48 2007 +0100
@@ -201,6 +201,11 @@ static void xenfb_update_screen(struct x
 
 	mutex_unlock(&info->mm_lock);
 
+	if (x2 < x1 || y2 < y1) {
+		printk("xenfb_update_screen bogus rect %d %d %d %d\n",
+		       x1, x2, y1, y2);
+		WARN_ON(1);
+	}
 	xenfb_do_update(info, x1, y1, x2 - x1, y2 - y1);
 }
 
@@ -252,7 +257,6 @@ static void xenfb_timer(unsigned long da
 static void xenfb_timer(unsigned long data)
 {
 	struct xenfb_info *info = (struct xenfb_info *)data;
-	info->dirty = 1;
 	wake_up(&info->wq);
 }
 
@@ -272,6 +276,7 @@ static void __xenfb_refresh(struct xenfb
 		info->x1 = x1;
 	if (info->x2 < x2)
 		info->x2 = x2;
+	info->dirty = 1;
 
 	if (timer_pending(&info->refresh))
 		return;

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Bogus screen update requests from buggy or malicous frontend make SDL
crash.  The VNC backend silently ignores them.  Catch and log them.

Signed-off-by: Markus Armbruster <armbru@redhat.com>


diff -r 837f83225153 tools/ioemu/hw/xenfb.c
--- a/tools/ioemu/hw/xenfb.c	Fri Nov 09 12:08:37 2007 +0000
+++ b/tools/ioemu/hw/xenfb.c	Tue Nov 13 17:30:22 2007 +0100
@@ -488,12 +488,27 @@ static void xenfb_on_fb_event(struct xen
 	rmb();			/* ensure we see ring contents up to prod */
 	for (cons = page->out_cons; cons != prod; cons++) {
 		union xenfb_out_event *event = &XENFB_OUT_RING_REF(page, cons);
+		int x, y, w, h;
 
 		switch (event->type) {
 		case XENFB_TYPE_UPDATE:
-			xenfb_guest_copy(xenfb,
-					 event->update.x, event->update.y,
-					 event->update.width, event->update.height);
+			x = MAX(event->update.x, 0);
+			y = MAX(event->update.y, 0);
+			w = MIN(event->update.width, xenfb->width - x);
+			h = MIN(event->update.height, xenfb->height - y);
+			if (w < 0 || h < 0) {
+				fprintf(stderr, "%s bogus update ignored\n",
+					xenfb->fb.nodename);
+				break;
+			}
+			if (x != event->update.x || y != event->update.y
+			    || w != event->update.width
+			    || h != event->update.height) {
+				fprintf(stderr, "%s bogus update clipped\n",
+					xenfb->fb.nodename);
+				break;
+			}
+			xenfb_guest_copy(xenfb, x, y, w, h);
 			break;
 		}
 	}

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