[PATCH v2] xen/gnttab: fix gnttab_acquire_resource()

[Juergen Gross <jgross@xxxxxxxx>]

Commit 9dc46386d89d ("gnttab: work around "may be used uninitialized"
warning") was wrong, as vaddrs can legitimately be NULL in case
XENMEM_resource_grant_table_id_status was specified for a grant table
v1. This would result in crashes in debug builds due to
ASSERT_UNREACHABLE() triggering.

Check vaddrs only to be NULL in the rc == 0 case.

Fixes: 9dc46386d89d ("gnttab: work around "may be used uninitialized" warning")
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Release-acked-by: Henry Wang <Henry.Wang@xxxxxxx>
---
Might be considered for backporting
---
 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 ad773a6996..fba329dcc2 100644
--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -4140,7 +4140,7 @@ int gnttab_acquire_resource(
      * on non-error paths, and hence it needs setting to NULL at the top of the
      * function.  Leave some runtime safety.
      */
-    if ( !vaddrs )
+    if ( !rc && !vaddrs )
     {
         ASSERT_UNREACHABLE();
         rc = -ENODATA;
-- 
2.35.3