Index: xen-3.2-testing/tools/ioemu/hw/xenfb.c
===================================================================
--- xen-3.2-testing.orig/tools/ioemu/hw/xenfb.c	2008-04-29 08:52:06.000000000 -0600
+++ xen-3.2-testing/tools/ioemu/hw/xenfb.c	2008-04-29 10:12:41.000000000 -0600
@@ -23,8 +23,6 @@
 #define BTN_LEFT 0x110 /* from <linux/input.h> */
 #endif
 
-// FIXME defend against malicious frontend?
-
 struct xenfb;
 
 struct xenfb_device {
@@ -50,6 +48,7 @@
 	int depth;              /* colour depth of guest framebuffer */
 	int width;              /* pixel width of guest framebuffer */
 	int height;             /* pixel height of guest framebuffer */
+	int offset;             /* offset of the framebuffer */
 	int abs_pointer_wanted; /* Whether guest supports absolute pointer */
 	int button_state;       /* Last seen pointer button state */
 	char protocol[64];	/* frontend protocol */
@@ -476,6 +475,75 @@
 	free(xenfb);
 }
 
+static int xenfb_configure_fb(struct xenfb *xenfb, size_t fb_len_lim,
+			      int width, int height, int depth,
+			      size_t fb_len, int offset, int row_stride)
+{
+	size_t mfn_sz = sizeof(*((struct xenfb_page *)0)->pd);
+	size_t pd_len = sizeof(((struct xenfb_page *)0)->pd) / mfn_sz;
+	size_t fb_pages = pd_len * XC_PAGE_SIZE / mfn_sz;
+	size_t fb_len_max = fb_pages * XC_PAGE_SIZE;
+	int max_width, max_height;
+
+	if (fb_len_lim == 0) {
+		fprintf(stderr,
+			"FB: No fb size limit, limit set to %zu\n",
+			fb_len_max);
+		fb_len_lim = fb_len_max;
+	}
+	if (fb_len_lim > fb_len_max) {
+		fprintf(stderr,
+			"FB: fb size limit %zu exceeds %zu, corrected\n",
+			fb_len_lim, fb_len_max);
+		fb_len_lim = fb_len_max;
+	}
+	if (fb_len > fb_len_lim) {
+		fprintf(stderr,
+			"FB: frontend fb size %zu limited to %zu\n",
+			fb_len, fb_len_lim);
+		fb_len = fb_len_lim;
+	}
+	if (depth != 8 && depth != 16 && depth != 24 && depth != 32) {
+		fprintf(stderr,
+			"FB: can't handle frontend fb depth %d\n",
+			depth);
+		return -1;
+	}
+	if (row_stride < 0 || row_stride > fb_len) {
+		fprintf(stderr,
+			"FB: invalid frontend stride %d\n", row_stride);
+		return -1;
+	}
+	max_width = row_stride / (depth / 8);
+	if (width < 0 || width > max_width) {
+		fprintf(stderr,
+			"FB: invalid frontend width %d limited to %d\n",
+			width, max_width);
+		width = max_width;
+	}
+	if (offset < 0 || offset >= fb_len) {
+		fprintf(stderr,
+			"FB: invalid frontend offset %d (max %zu)\n",
+			offset, fb_len - 1);
+		return -1;
+	}
+	max_height = (fb_len - offset) / row_stride;
+	if (height < 0 || height > max_height) {
+		fprintf(stderr,
+			"FB: invalid frontend height %d limited to %d\n",
+			height, max_height);
+		height = max_height;
+	}
+	xenfb->fb_len = fb_len;
+	xenfb->row_stride = row_stride;
+	xenfb->depth = depth;
+	xenfb->width = width;
+	xenfb->height = height;
+	xenfb->offset = offset;
+	fprintf(stderr, "Framebuffer %dx%dx%d offset %d stride %d\n",
+		width, height, depth, offset, row_stride);
+	return 0;
+}
 
 static void xenfb_on_fb_event(struct xenfb *xenfb)
 {
@@ -511,10 +579,17 @@
 			xenfb_guest_copy(xenfb, x, y, w, h);
 			break;
 		case XENFB_TYPE_RESIZE:
-			xenfb->width  = event->resize.width;
-			xenfb->height = event->resize.height;
-			xenfb->row_stride = event->resize.stride;
+            if (xenfb_configure_fb(xenfb, xenfb->fb_len,
+                           event->resize.width,
+                           event->resize.height,
+                           event->resize.depth,
+                           xenfb->fb_len,
+                           0,
+                           event->resize.stride) < 0)
+                break;
+
 			dpy_resize(xenfb->ds, xenfb->width, xenfb->height);
+			xenfb_invalidate(xenfb);
 			break;
 		}
 	}
@@ -695,22 +770,14 @@
 
         if (xenfb_xs_scanf1(xenfb->xsh, xenfb->fb.nodename, "videoram", "%d", &videoram) < 0)
                 videoram = 0;
-        videoram = videoram * 1024 * 1024;
 
         fb_page = xenfb->fb.page;
-        xenfb->depth = fb_page->depth;
-        xenfb->width = fb_page->width;
-        xenfb->height = fb_page->height;
-        xenfb->fb_len = fb_page->mem_length;
-        xenfb->row_stride = fb_page->line_length;
-        /* Protect against hostile frontend, limit fb_len to configured */
-        if (videoram && xenfb->fb_len > videoram) {
-                xenfb->fb_len = videoram;
-                if (xenfb->row_stride * xenfb->height > xenfb->fb_len)
-                        xenfb->height = xenfb->fb_len / xenfb->row_stride;
+        if (xenfb_configure_fb(xenfb, videoram * 1024 * 1024U,
+                               fb_page->width, fb_page->height, fb_page->depth,
+                               fb_page->mem_length, 0, fb_page->line_length) < 0) {
+                errno = EINVAL;
+                return -1;
         }
-        fprintf(stderr, "Framebuffer depth %d width %d height %d line %d\n",
-                fb_page->depth, fb_page->width, fb_page->height, fb_page->line_length);
         if (xenfb_map_fb(xenfb, xenfb->fb.otherend_id) < 0)
 		return -1;