Derived from
# HG changeset patch
# User Keir Fraser <keir.fraser@citrix.com>
# Date 1210687697 -3600
# Node ID 53195719f7621110dab7a97a2bca292b73baa715
# Parent  65eec0554f39049eab354abe1ee4c305f6d1e0aa
ioemu: Fix PVFB backend to validate frontend's frame buffer description

diff -rup a/tools/ioemu/hw/xenfb.c b/tools/ioemu/hw/xenfb.c
--- a/tools/ioemu/hw/xenfb.c	2008-04-22 18:51:35.000000000 +0200
+++ b/tools/ioemu/hw/xenfb.c	2008-04-22 18:52:07.000000000 +0200
@@ -23,8 +23,6 @@
 #define BTN_LEFT 0x110 /* from <linux/input.h> */
 #endif
 
-// FIXME defend against malicious frontend?
-
 struct xenfb;
 
 struct xenfb_device {
@@ -476,6 +474,56 @@ void xenfb_shutdown(struct xenfb *xenfb)
 	free(xenfb);
 }
 
+static int xenfb_configure_fb(struct xenfb *xenfb,
+			      int width, int height, int depth,
+			      size_t fb_len, 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_lim = fb_pages * XC_PAGE_SIZE;
+	int max_width, max_height;
+
+	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;
+	}
+	max_height = fb_len / 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;
+	fprintf(stderr, "Framebuffer %dx%dx%d stride %d\n",
+		width, height, depth, row_stride);
+	return 0;
+}
 
 static void xenfb_on_fb_event(struct xenfb *xenfb)
 {
@@ -506,7 +553,6 @@ static void xenfb_on_fb_event(struct xen
 			    || h != event->update.height) {
 				fprintf(stderr, "%s bogus update clipped\n",
 					xenfb->fb.nodename);
-				break;
 			}
 			xenfb_guest_copy(xenfb, x, y, w, h);
 			break;
@@ -686,16 +732,15 @@ static int xenfb_read_frontend_fb_config
                 xenfb->protocol[0] = '\0';
         xenfb_xs_printf(xenfb->xsh, xenfb->fb.nodename, "request-update", "1");
 
-        /* TODO check for permitted ranges */
         fb_page = xenfb->fb.page;
-        xenfb->depth = fb_page->depth;
-        xenfb->width = fb_page->width;
-        xenfb->height = fb_page->height;
-        /* TODO check for consistency with the above */
-        xenfb->fb_len = fb_page->mem_length;
-        xenfb->row_stride = fb_page->line_length;
-        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_configure_fb(xenfb,
+			       fb_page->width, fb_page->height, fb_page->depth,
+			       fb_page->mem_length, fb_page->line_length)
+	    < 0) {
+		errno = EINVAL;
+		return -1;
+	}
+
         if (xenfb_map_fb(xenfb, xenfb->fb.otherend_id) < 0)
 		return -1;