266 lines
6.3 KiB
C
266 lines
6.3 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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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/sched/user.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/binfmts.h>
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#include <linux/proc_ns.h>
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#if IS_ENABLED(CONFIG_BINFMT_MISC)
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struct binfmt_misc init_binfmt_misc = {
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.entries = LIST_HEAD_INIT(init_binfmt_misc.entries),
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.enabled = true,
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.entries_lock = __RW_LOCK_UNLOCKED(init_binfmt_misc.entries_lock),
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};
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EXPORT_SYMBOL_GPL(init_binfmt_misc);
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#endif
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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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{
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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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},
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.gid_map = {
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.nr_extents = 1,
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{
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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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},
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.projid_map = {
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.nr_extents = 1,
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{
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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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},
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.ns.count = REFCOUNT_INIT(3),
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.owner = GLOBAL_ROOT_UID,
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.group = GLOBAL_ROOT_GID,
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.ns.inum = PROC_USER_INIT_INO,
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#ifdef CONFIG_USER_NS
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.ns.ops = &userns_operations,
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#endif
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.flags = USERNS_INIT_FLAGS,
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#ifdef CONFIG_KEYS
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.keyring_name_list = LIST_HEAD_INIT(init_user_ns.keyring_name_list),
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.keyring_sem = __RWSEM_INITIALIZER(init_user_ns.keyring_sem),
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#endif
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#if IS_ENABLED(CONFIG_BINFMT_MISC)
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.binfmt_misc = &init_binfmt_misc,
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#endif
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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 (IS_ENABLED(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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static 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 = REFCOUNT_INIT(1),
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.uid = GLOBAL_ROOT_UID,
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.ratelimit = RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0),
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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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refcount_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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static int user_epoll_alloc(struct user_struct *up)
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{
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#ifdef CONFIG_EPOLL
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return percpu_counter_init(&up->epoll_watches, 0, GFP_KERNEL);
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#else
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return 0;
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#endif
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}
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static void user_epoll_free(struct user_struct *up)
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{
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#ifdef CONFIG_EPOLL
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percpu_counter_destroy(&up->epoll_watches);
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#endif
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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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user_epoll_free(up);
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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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if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))
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free_user(up, flags);
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}
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EXPORT_SYMBOL_GPL(free_uid);
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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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return NULL;
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new->uid = uid;
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refcount_set(&new->__count, 1);
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if (user_epoll_alloc(new)) {
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kmem_cache_free(uid_cachep, new);
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return NULL;
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}
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ratelimit_state_init(&new->ratelimit, HZ, 100);
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ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE);
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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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user_epoll_free(new);
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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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}
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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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if (user_epoll_alloc(&root_user))
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panic("root_user epoll percpu counter alloc failed");
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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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subsys_initcall(uid_cache_init);
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