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

Serge E. Hallyn
2012-04-18T18:47:54Z

Quoting Eric W. Beiderman (ebiederm@xmission.com):
> 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;

I think in the past the creator cred pinned the ns->parent. Do you now
need to explicitly pin ns->parent (and release it in free_user_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
>
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