userns: limit the maximum depth of user_namespace->parent chain
Ensure that user_namespace->parent chain can't grow too much.
Currently we use the hardroded 32 as limit.
Reported-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index b6b215f..14105c2 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -23,6 +23,7 @@
struct uid_gid_map projid_map;
atomic_t count;
struct user_namespace *parent;
+ int level;
kuid_t owner;
kgid_t group;
unsigned int proc_inum;