From c3d830b244998b3686e2eb64db95996be5eb5e5c Mon Sep 17 00:00:00 2001
From: Andrew Cooper <andrew.cooper3@citrix.com>
Date: Tue, 12 Sep 2017 14:44:11 +0200
Subject: [PATCH] grant_table: fix GNTTABOP_cache_flush handling

Don't fall over a NULL grant_table pointer when the owner of the domain
is a system domain (DOMID_{XEN,IO} etc).

This is CVE-2017-14318 / XSA-232.

Reported-by: Matthew Daley <mattd@bugfuzz.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
 xen/common/grant_table.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
index fb3859ce8e..c3895e6201 100644
--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -3046,7 +3046,7 @@ static int cache_flush(gnttab_cache_flush_t *cflush, grant_ref_t *cur_ref)
 
     page = mfn_to_page(mfn);
     owner = page_get_owner_and_reference(page);
-    if ( !owner )
+    if ( !owner || !owner->grant_table )
     {
         rcu_unlock_domain(d);
         return -EPERM;
-- 
2.30.2