Commit 783291e6 authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

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



- 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: default avatarSerge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: default avatarEric W. Biederman <ebiederm@xmission.com>
parent 7b44ab97

include/linux/user_namespace.h

+2 −2
Original line number Diff line number Diff line
@@ -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;

kernel/user.c

+4 −3
Original line number Diff line number Diff line
@@ -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),

kernel/user_namespace.c

+20 −22
Original line number Diff line number Diff line
@@ -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;
@@ -63,35 +75,22 @@ 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)

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 +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;

		}

	}

security/commoncap.c

+3 −2
Original line number Diff line number Diff line
@@ -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? */

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