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userns: Simplify the user_namespace by making userns->creator a kuid.

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- 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.

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2011-11-17 01:32:59 -08:00
parent 7b44ab978b
commit 783291e690
4 changed files with 30 additions and 30 deletions
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4
include/linux/user_namespace.h
View File

@ -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;

7
kernel/user.c
View File

@ -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),

44
kernel/user_namespace.c
View File

@ -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;
@ -63,34 +75,21 @@ int create_user_ns(struct cred *new)
#endif
/* tgcred will be cleared in our caller bc CLONE_THREAD won't be set */
/* Leave the reference to our user_ns with the new cred */
/* Leave the new->user_ns reference with the new user namespace. */
/* Leave the reference to our user_ns with the new cred. */
new->user_ns = ns;
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)
{
struct user_namespace *parent, *ns =
container_of(work, struct user_namespace, destroyer);
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 =
struct user_namespace *parent, *ns =
container_of(kref, struct user_namespace, kref);
INIT_WORK(&ns->destroyer, free_user_ns_work);
schedule_work(&ns->destroyer);
parent = ns->parent;
kmem_cache_free(user_ns_cachep, ns);
put_user_ns(parent);
}
EXPORT_SYMBOL(free_user_ns);
@ -101,12 +100,11 @@ 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 +124,7 @@ 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;
}
}

5
security/commoncap.c
View File

@ -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? */