Only allow unprivileged mounts of proc and sysfs if they are already mounted when the user namespace is created. proc and sysfs are interesting because they have content that is per namespace, and so fresh mounts are needed when new namespaces are created while at the same time proc and sysfs have content that is shared between every instance. Respect the policy of who may see the shared content of proc and sysfs by only allowing new mounts if there was an existing mount at the time the user namespace was created. In practice there are only two interesting cases: proc and sysfs are mounted at their usual places, proc and sysfs are not mounted at all (some form of mount namespace jail). Cc: stable@vger.kernel.org Acked-by: Serge Hallyn <serge.hallyn@canonical.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
224 lines
5.2 KiB
C
224 lines
5.2 KiB
C
/*
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* The "user cache".
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*
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* (C) Copyright 1991-2000 Linus Torvalds
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*
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* We have a per-user structure to keep track of how many
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* processes, files etc the user has claimed, in order to be
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* able to have per-user limits for system resources.
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*/
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#include <linux/init.h>
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#include <linux/sched.h>
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#include <linux/slab.h>
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#include <linux/bitops.h>
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#include <linux/key.h>
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#include <linux/interrupt.h>
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#include <linux/export.h>
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#include <linux/user_namespace.h>
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#include <linux/proc_fs.h>
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/*
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* userns count is 1 for root user, 1 for init_uts_ns,
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* and 1 for... ?
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*/
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struct user_namespace init_user_ns = {
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.uid_map = {
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.nr_extents = 1,
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.extent[0] = {
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.first = 0,
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.lower_first = 0,
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.count = 4294967295U,
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},
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},
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.gid_map = {
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.nr_extents = 1,
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.extent[0] = {
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.first = 0,
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.lower_first = 0,
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.count = 4294967295U,
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},
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},
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.projid_map = {
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.nr_extents = 1,
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.extent[0] = {
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.first = 0,
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.lower_first = 0,
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.count = 4294967295U,
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},
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},
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.count = ATOMIC_INIT(3),
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.owner = GLOBAL_ROOT_UID,
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.group = GLOBAL_ROOT_GID,
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.proc_inum = PROC_USER_INIT_INO,
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.may_mount_sysfs = true,
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.may_mount_proc = true,
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};
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EXPORT_SYMBOL_GPL(init_user_ns);
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/*
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* UID task count cache, to get fast user lookup in "alloc_uid"
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* when changing user ID's (ie setuid() and friends).
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*/
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#define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7)
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#define UIDHASH_SZ (1 << UIDHASH_BITS)
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#define UIDHASH_MASK (UIDHASH_SZ - 1)
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#define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
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#define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid))))
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static struct kmem_cache *uid_cachep;
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struct hlist_head uidhash_table[UIDHASH_SZ];
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/*
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* The uidhash_lock is mostly taken from process context, but it is
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* occasionally also taken from softirq/tasklet context, when
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* task-structs get RCU-freed. Hence all locking must be softirq-safe.
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* But free_uid() is also called with local interrupts disabled, and running
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* local_bh_enable() with local interrupts disabled is an error - we'll run
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* softirq callbacks, and they can unconditionally enable interrupts, and
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* the caller of free_uid() didn't expect that..
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*/
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static DEFINE_SPINLOCK(uidhash_lock);
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/* root_user.__count is 1, for init task cred */
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struct user_struct root_user = {
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.__count = ATOMIC_INIT(1),
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.processes = ATOMIC_INIT(1),
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.files = ATOMIC_INIT(0),
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.sigpending = ATOMIC_INIT(0),
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.locked_shm = 0,
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.uid = GLOBAL_ROOT_UID,
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};
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/*
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* These routines must be called with the uidhash spinlock held!
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*/
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static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
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{
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hlist_add_head(&up->uidhash_node, hashent);
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}
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static void uid_hash_remove(struct user_struct *up)
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{
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hlist_del_init(&up->uidhash_node);
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}
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static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
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{
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struct user_struct *user;
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hlist_for_each_entry(user, hashent, uidhash_node) {
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if (uid_eq(user->uid, uid)) {
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atomic_inc(&user->__count);
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return user;
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}
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}
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return NULL;
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}
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/* IRQs are disabled and uidhash_lock is held upon function entry.
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* IRQ state (as stored in flags) is restored and uidhash_lock released
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* upon function exit.
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*/
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static void free_user(struct user_struct *up, unsigned long flags)
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__releases(&uidhash_lock)
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{
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uid_hash_remove(up);
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spin_unlock_irqrestore(&uidhash_lock, flags);
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key_put(up->uid_keyring);
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key_put(up->session_keyring);
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kmem_cache_free(uid_cachep, up);
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}
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/*
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* Locate the user_struct for the passed UID. If found, take a ref on it. The
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* caller must undo that ref with free_uid().
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*
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* If the user_struct could not be found, return NULL.
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*/
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struct user_struct *find_user(kuid_t uid)
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{
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struct user_struct *ret;
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unsigned long flags;
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spin_lock_irqsave(&uidhash_lock, flags);
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ret = uid_hash_find(uid, uidhashentry(uid));
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spin_unlock_irqrestore(&uidhash_lock, flags);
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return ret;
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}
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void free_uid(struct user_struct *up)
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{
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unsigned long flags;
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if (!up)
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return;
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local_irq_save(flags);
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if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
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free_user(up, flags);
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else
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local_irq_restore(flags);
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}
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struct user_struct *alloc_uid(kuid_t uid)
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{
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struct hlist_head *hashent = uidhashentry(uid);
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struct user_struct *up, *new;
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spin_lock_irq(&uidhash_lock);
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up = uid_hash_find(uid, hashent);
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spin_unlock_irq(&uidhash_lock);
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if (!up) {
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new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
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if (!new)
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goto out_unlock;
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new->uid = uid;
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atomic_set(&new->__count, 1);
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/*
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* Before adding this, check whether we raced
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* on adding the same user already..
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*/
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spin_lock_irq(&uidhash_lock);
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up = uid_hash_find(uid, hashent);
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if (up) {
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key_put(new->uid_keyring);
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key_put(new->session_keyring);
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kmem_cache_free(uid_cachep, new);
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} else {
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uid_hash_insert(new, hashent);
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up = new;
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}
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spin_unlock_irq(&uidhash_lock);
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}
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return up;
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out_unlock:
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return NULL;
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}
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static int __init uid_cache_init(void)
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{
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int n;
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uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
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0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
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for(n = 0; n < UIDHASH_SZ; ++n)
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INIT_HLIST_HEAD(uidhash_table + n);
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/* Insert the root user immediately (init already runs as root) */
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spin_lock_irq(&uidhash_lock);
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uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
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spin_unlock_irq(&uidhash_lock);
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return 0;
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}
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module_init(uid_cache_init);
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