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;
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 6e50a44..9064b91 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -62,6 +62,9 @@
kgid_t group = new->egid;
int ret;
+ if (parent_ns->level > 32)
+ return -EUSERS;
+
/*
* Verify that we can not violate the policy of which files
* may be accessed that is specified by the root directory,
@@ -92,6 +95,7 @@
atomic_set(&ns->count, 1);
/* Leave the new->user_ns reference with the new user namespace. */
ns->parent = parent_ns;
+ ns->level = parent_ns->level + 1;
ns->owner = owner;
ns->group = group;