[PATCH 16/43] userns: Simplify the user_namespace by making userns->creator a kuid.

"Eric W. Beiderman
2012-04-08T05:12:59Z

From: Eric W. Biederman <ebiederm@xmission.com>

- Transform userns->creator from a user_struct reference to a simple
kuid_t, kgid_t pair.

In cap_capable this allows the check to see if we are the creator of
a namespace to become the classic suser style euid permission check.

This allows us to remove the need for a struct cred in the mapping
functions and still be able to dispaly the user namespace creators
uid and gid as 0.

- Remove the now unnecessary delayed_work in free_user_ns.

All that is left for free_user_ns to do is to call kmem_cache_free
and put_user_ns. Those functions can be called in any context
so call them directly from free_user_ns removing the need for delayed work.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---
include/linux/user_namespace.h | 4 ++--
kernel/user.c | 7 ++++---
kernel/user_namespace.c | 39 ++++++++++++++++++---------------------
security/commoncap.c | 5 +++--
4 files changed, 27 insertions(+), 28 deletions(-)

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index d767508..8a391bd 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -9,8 +9,8 @@
struct user_namespace {
struct kref kref;
struct user_namespace *parent;
- struct user_struct *creator;
- struct work_struct destroyer;
+ kuid_t owner;
+ kgid_t group;
};

extern struct user_namespace init_user_ns;
diff --git a/kernel/user.c b/kernel/user.c
index 025077e..cff3856 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -25,7 +25,8 @@ struct user_namespace init_user_ns = {
.kref = {
.refcount = ATOMIC_INIT(3),
},
- .creator = &root_user,
+ .owner = GLOBAL_ROOT_UID,
+ .group = GLOBAL_ROOT_GID,
};
EXPORT_SYMBOL_GPL(init_user_ns);

@@ -54,9 +55,9 @@ struct hlist_head uidhash_table[UIDHASH_SZ];
*/
static DEFINE_SPINLOCK(uidhash_lock);

-/* root_user.__count is 2, 1 for init task cred, 1 for init_user_ns->user_ns */
+/* root_user.__count is 1, for init task cred */
struct user_struct root_user = {
- .__count = ATOMIC_INIT(2),
+ .__count = ATOMIC_INIT(1),
.processes = ATOMIC_INIT(1),
.files = ATOMIC_INIT(0),
.sigpending = ATOMIC_INIT(0),
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 898e973..f69741a 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -27,6 +27,16 @@ int create_user_ns(struct cred *new)
{
struct user_namespace *ns, *parent_ns = new->user_ns;
struct user_struct *root_user;
+ kuid_t owner = make_kuid(new->user_ns, new->euid);
+ kgid_t group = make_kgid(new->user_ns, new->egid);
+
+ /* The creator needs a mapping in the parent user namespace
+ * or else we won't be able to reasonably tell userspace who
+ * created a user_namespace.
+ */
+ if (!kuid_has_mapping(parent_ns, owner) ||
+ !kgid_has_mapping(parent_ns, group))
+ return -EPERM;

ns = kmem_cache_alloc(user_ns_cachep, GFP_KERNEL);
if (!ns)
@@ -43,7 +53,9 @@ int create_user_ns(struct cred *new)

/* set the new root user in the credentials under preparation */
ns->parent = parent_ns;
- ns->creator = new->user;
+ ns->owner = owner;
+ ns->group = group;
+ free_uid(new->user);
new->user = root_user;
new->uid = new->euid = new->suid = new->fsuid = 0;
new->gid = new->egid = new->sgid = new->fsgid = 0;
@@ -69,29 +81,15 @@ int create_user_ns(struct cred *new)
return 0;
}

-/*
- * Deferred destructor for a user namespace. This is required because
- * free_user_ns() may be called with uidhash_lock held, but we need to call
- * back to free_uid() which will want to take the lock again.
- */
-static void free_user_ns_work(struct work_struct *work)
+void free_user_ns(struct kref *kref)
{
struct user_namespace *parent, *ns =
- container_of(work, struct user_namespace, destroyer);
+ container_of(kref, struct user_namespace, kref);
+
parent = ns->parent;
- free_uid(ns->creator);
kmem_cache_free(user_ns_cachep, ns);
put_user_ns(parent);
}
-
-void free_user_ns(struct kref *kref)
-{
- struct user_namespace *ns =
- container_of(kref, struct user_namespace, kref);
-
- INIT_WORK(&ns->destroyer, free_user_ns_work);
- schedule_work(&ns->destroyer);
-}
EXPORT_SYMBOL(free_user_ns);

uid_t user_ns_map_uid(struct user_namespace *to, const struct cred *cred, uid_t uid)
@@ -101,12 +99,11 @@ uid_t user_ns_map_uid(struct user_namespace *to, const struct cred *cred, uid_t
if (likely(to == cred->user_ns))
return uid;

-
/* Is cred->user the creator of the target user_ns
* or the creator of one of it's parents?
*/
for ( tmp = to; tmp != &init_user_ns; tmp = tmp->parent ) {
- if (cred->user == tmp->creator) {
+ if (uid_eq(cred->user->uid, tmp->owner)) {
return (uid_t)0;
}
}
@@ -126,7 +123,7 @@ gid_t user_ns_map_gid(struct user_namespace *to, const struct cred *cred, gid_t
* or the creator of one of it's parents?
*/
for ( tmp = to; tmp != &init_user_ns; tmp = tmp->parent ) {
- if (cred->user == tmp->creator) {
+ if (uid_eq(cred->user->uid, tmp->owner)) {
return (gid_t)0;
}
}
diff --git a/security/commoncap.c b/security/commoncap.c
index 435d074..f2399d8 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -76,8 +76,9 @@ int cap_capable(const struct cred *cred, struct user_namespace *targ_ns,
int cap, int audit)
{
for (;;) {
- /* The creator of the user namespace has all caps. */
- if (targ_ns != &init_user_ns && targ_ns->creator == cred->user)
+ /* The owner of the user namespace has all caps. */
+ if (targ_ns != &init_user_ns && uid_eq(targ_ns->owner,
+ make_kuid(cred->user_ns, cred->euid)))
return 0;

/* Do we have the necessary capabilities? */
--
1.7.2.5