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$NetBSD: patch-CVE-2013-4494,v 1.1 2013/11/23 14:04:59 drochner Exp $
http://lists.xenproject.org/archives/html/xen-devel/2013-11/msg00225.html
--- xen/common/grant_table.c.orig 2013-09-10 06:42:18.000000000 +0000
+++ xen/common/grant_table.c 2013-11-19 16:46:13.000000000 +0000
@@ -1459,6 +1459,8 @@ gnttab_transfer(
for ( i = 0; i < count; i++ )
{
+ bool_t okay;
+
if (i && hypercall_preempt_check())
return i;
@@ -1555,16 +1557,18 @@ gnttab_transfer(
* pages when it is dying.
*/
if ( unlikely(e->is_dying) ||
- unlikely(e->tot_pages >= e->max_pages) ||
- unlikely(!gnttab_prepare_for_transfer(e, d, gop.ref)) )
+ unlikely(e->tot_pages >= e->max_pages) )
{
- if ( !e->is_dying )
- gdprintk(XENLOG_INFO, "gnttab_transfer: "
- "Transferee has no reservation "
- "headroom (%d,%d) or provided a bad grant ref (%08x) "
- "or is dying (%d)\n",
- e->tot_pages, e->max_pages, gop.ref, e->is_dying);
spin_unlock(&e->page_alloc_lock);
+
+ if ( e->is_dying )
+ gdprintk(XENLOG_INFO, "gnttab_transfer: "
+ "Transferee (d%d) is dying\n", e->domain_id);
+ else
+ gdprintk(XENLOG_INFO, "gnttab_transfer: "
+ "Transferee (d%d) has no headroom (tot %u, max %u)\n",
+ e->domain_id, e->tot_pages, e->max_pages);
+
rcu_unlock_domain(e);
page->count_info &= ~(PGC_count_mask|PGC_allocated);
free_domheap_page(page);
@@ -1575,6 +1579,37 @@ gnttab_transfer(
/* Okay, add the page to 'e'. */
if ( unlikely(e->tot_pages++ == 0) )
get_knownalive_domain(e);
+
+ /*
+ * We must drop the lock to avoid a possible deadlock in
+ * gnttab_prepare_for_transfer. We have reserved a page in e so can
+ * safely drop the lock and re-aquire it later to add page to the
+ * pagelist.
+ */
+ spin_unlock(&e->page_alloc_lock);
+ okay = gnttab_prepare_for_transfer(e, d, gop.ref);
+ spin_lock(&e->page_alloc_lock);
+
+ if ( unlikely(!okay) || unlikely(e->is_dying) )
+ {
+ bool_t drop_dom_ref = (e->tot_pages-- == 1);
+
+ spin_unlock(&e->page_alloc_lock);
+
+ if ( okay /* i.e. e->is_dying due to the surrounding if() */ )
+ gdprintk(XENLOG_INFO, "gnttab_transfer: "
+ "Transferee (d%d) is now dying\n", e->domain_id);
+
+ if ( drop_dom_ref )
+ put_domain(e);
+ rcu_unlock_domain(e);
+
+ page->count_info &= ~(PGC_count_mask|PGC_allocated);
+ free_domheap_page(page);
+ gop.status = GNTST_general_error;
+ goto copyback;
+ }
+
page_list_add_tail(page, &e->page_list);
page_set_owner(page, e);
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