userns: Don't read extents twice in m_start
This is important so reading /proc/<pid>/{uid_map,gid_map,projid_map} while
the map is being written does not do strange things.
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 563a298..4f7e357 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -683,11 +683,13 @@
struct uid_gid_map *map)
{
loff_t pos = *ppos;
+ unsigned extents = map->nr_extents;
+ smp_rmb();
- if (pos >= map->nr_extents)
+ if (pos >= extents)
return NULL;
- if (map->nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
+ if (extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
return &map->extent[pos];
return &map->forward[pos];