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userns: limit the maximum depth of user_namespace->parent chain

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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>
This commit is contained in:
Oleg Nesterov 2013-08-08 18:55:32 +02:00 • committed by Linus Torvalds
parent 55f5bfd4c9
commit 8742f229b6
2 changed files with 5 additions and 0 deletions
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1
include/linux/user_namespace.h
View file

@ -23,6 +23,7 @@ struct user_namespace {
struct uid_gid_map projid_map; struct uid_gid_map projid_map;
atomic_t count; atomic_t count;
struct user_namespace *parent; struct user_namespace *parent;
int level;
kuid_t owner; kuid_t owner;
kgid_t group; kgid_t group;
unsigned int proc_inum; unsigned int proc_inum;

4
kernel/user_namespace.c
View file

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