// SPDX-License-Identifier: GPL-2.0-only/* * The "user cache". * * (C) Copyright 1991-2000 Linus Torvalds * * We have a per-user structure to keep track of how many * processes, files etc the user has claimed, in order to be * able to have per-user limits for system resources.  */ #include <linux/init.h>#include <linux/sched.h>#include <linux/slab.h>#include <linux/bitops.h>#include <linux/key.h>#include <linux/sched/user.h>#include <linux/interrupt.h>#include <linux/export.h>#include <linux/user_namespace.h>#include <linux/binfmts.h>#include <linux/proc_ns.h> #if IS_ENABLED(CONFIG_BINFMT_MISC)struct binfmt_misc init_binfmt_misc = {	.entries = HLIST_HEAD_INIT,	.enabled = true,	.entries_lock = __SPIN_LOCK_UNLOCKED(init_binfmt_misc.entries_lock),};EXPORT_SYMBOL_GPL(init_binfmt_misc);#endif /* * userns count is 1 for root user, 1 for init_uts_ns, * and 1 for... ? */struct user_namespace init_user_ns = {	.ns = NS_COMMON_INIT(init_user_ns),	.uid_map = {		{			.extent[0] = {				.first = 0,				.lower_first = 0,				.count = 4294967295U,			},			.nr_extents = 1,		},	},	.gid_map = {		{			.extent[0] = {				.first = 0,				.lower_first = 0,				.count = 4294967295U,			},			.nr_extents = 1,		},	},	.projid_map = {		{			.extent[0] = {				.first = 0,				.lower_first = 0,				.count = 4294967295U,			},			.nr_extents = 1,		},	},	.owner = GLOBAL_ROOT_UID,	.group = GLOBAL_ROOT_GID,	.flags = USERNS_INIT_FLAGS,#ifdef CONFIG_KEYS	.keyring_name_list = LIST_HEAD_INIT(init_user_ns.keyring_name_list),	.keyring_sem = __RWSEM_INITIALIZER(init_user_ns.keyring_sem),#endif#if IS_ENABLED(CONFIG_BINFMT_MISC)	.binfmt_misc = &init_binfmt_misc,#endif};EXPORT_SYMBOL_GPL(init_user_ns); /* * UID task count cache, to get fast user lookup in "alloc_uid" * when changing user ID's (ie setuid() and friends). */ #define UIDHASH_BITS	(IS_ENABLED(CONFIG_BASE_SMALL) ? 3 : 7)#define UIDHASH_SZ	(1 << UIDHASH_BITS)#define UIDHASH_MASK		(UIDHASH_SZ - 1)#define __uidhashfn(uid)	(((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)#define uidhashentry(uid)	(uidhash_table + __uidhashfn((__kuid_val(uid)))) static struct kmem_cache *uid_cachep;static struct hlist_head uidhash_table[UIDHASH_SZ]; /* * The uidhash_lock is mostly taken from process context, but it is * occasionally also taken from softirq/tasklet context, when * task-structs get RCU-freed. Hence all locking must be softirq-safe. * But free_uid() is also called with local interrupts disabled, and running * local_bh_enable() with local interrupts disabled is an error - we'll run * softirq callbacks, and they can unconditionally enable interrupts, and * the caller of free_uid() didn't expect that.. */static DEFINE_SPINLOCK(uidhash_lock); /* root_user.__count is 1, for init task cred */struct user_struct root_user = {	.__count	= REFCOUNT_INIT(1),	.uid		= GLOBAL_ROOT_UID,	.ratelimit	= RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0),}; /* * These routines must be called with the uidhash spinlock held! */static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent){	hlist_add_head(&up->uidhash_node, hashent);} static void uid_hash_remove(struct user_struct *up){	hlist_del_init(&up->uidhash_node);} static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent){	struct user_struct *user; 	hlist_for_each_entry(user, hashent, uidhash_node) {		if (uid_eq(user->uid, uid)) {			refcount_inc(&user->__count);			return user;		}	} 	return NULL;} static int user_epoll_alloc(struct user_struct *up){#ifdef CONFIG_EPOLL	return percpu_counter_init(&up->epoll_watches, 0, GFP_KERNEL);#else	return 0;#endif} static void user_epoll_free(struct user_struct *up){#ifdef CONFIG_EPOLL	percpu_counter_destroy(&up->epoll_watches);#endif} /* IRQs are disabled and uidhash_lock is held upon function entry. * IRQ state (as stored in flags) is restored and uidhash_lock released * upon function exit. */static void free_user(struct user_struct *up, unsigned long flags)	__releases(&uidhash_lock){	uid_hash_remove(up);	spin_unlock_irqrestore(&uidhash_lock, flags);	user_epoll_free(up);	kmem_cache_free(uid_cachep, up);} /* * Locate the user_struct for the passed UID.  If found, take a ref on it.  The * caller must undo that ref with free_uid(). * * If the user_struct could not be found, return NULL. */struct user_struct *find_user(kuid_t uid){	struct user_struct *ret;	unsigned long flags; 	spin_lock_irqsave(&uidhash_lock, flags);	ret = uid_hash_find(uid, uidhashentry(uid));	spin_unlock_irqrestore(&uidhash_lock, flags);	return ret;} void free_uid(struct user_struct *up){	unsigned long flags; 	if (!up)		return; 	if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))		free_user(up, flags);}EXPORT_SYMBOL_GPL(free_uid); struct user_struct *alloc_uid(kuid_t uid){	struct hlist_head *hashent = uidhashentry(uid);	struct user_struct *up, *new; 	spin_lock_irq(&uidhash_lock);	up = uid_hash_find(uid, hashent);	spin_unlock_irq(&uidhash_lock); 	if (!up) {		new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);		if (!new)			return NULL; 		new->uid = uid;		refcount_set(&new->__count, 1);		if (user_epoll_alloc(new)) {			kmem_cache_free(uid_cachep, new);			return NULL;		}		ratelimit_state_init(&new->ratelimit, HZ, 100);		ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE); 		/*		 * Before adding this, check whether we raced		 * on adding the same user already..		 */		spin_lock_irq(&uidhash_lock);		up = uid_hash_find(uid, hashent);		if (up) {			user_epoll_free(new);			kmem_cache_free(uid_cachep, new);		} else {			uid_hash_insert(new, hashent);			up = new;		}		spin_unlock_irq(&uidhash_lock);	} 	return up;} static int __init uid_cache_init(void){	int n; 	uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); 	for(n = 0; n < UIDHASH_SZ; ++n)		INIT_HLIST_HEAD(uidhash_table + n); 	if (user_epoll_alloc(&root_user))		panic("root_user epoll percpu counter alloc failed"); 	/* Insert the root user immediately (init already runs as root) */	spin_lock_irq(&uidhash_lock);	uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));	spin_unlock_irq(&uidhash_lock); 	return 0;}subsys_initcall(uid_cache_init);