/* * 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/interrupt.h>#include <linux/module.h>#include <linux/user_namespace.h> /* * userns count is 1 for root user, 1 for init_uts_ns, * and 1 for... ? */struct user_namespace init_user_ns = {	.kref = {		.refcount	= ATOMIC_INIT(3),	},	.creator = &root_user,};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_MASK		(UIDHASH_SZ - 1)#define __uidhashfn(uid)	(((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)#define uidhashentry(ns, uid)	((ns)->uidhash_table + __uidhashfn((uid))) static struct kmem_cache *uid_cachep; /* * 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 2, 1 for init task cred, 1 for init_user_ns->user_ns */struct user_struct root_user = {	.__count	= ATOMIC_INIT(2),	.processes	= ATOMIC_INIT(1),	.files		= ATOMIC_INIT(0),	.sigpending	= ATOMIC_INIT(0),	.locked_shm     = 0,	.user_ns	= &init_user_ns,}; /* * 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);	put_user_ns(up->user_ns);} static struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent){	struct user_struct *user;	struct hlist_node *h; 	hlist_for_each_entry(user, h, hashent, uidhash_node) {		if (user->uid == uid) {			atomic_inc(&user->__count);			return user;		}	} 	return NULL;} /* 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);	key_put(up->uid_keyring);	key_put(up->session_keyring);	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(uid_t uid){	struct user_struct *ret;	unsigned long flags;	struct user_namespace *ns = current_user_ns(); 	spin_lock_irqsave(&uidhash_lock, flags);	ret = uid_hash_find(uid, uidhashentry(ns, uid));	spin_unlock_irqrestore(&uidhash_lock, flags);	return ret;} void free_uid(struct user_struct *up){	unsigned long flags; 	if (!up)		return; 	local_irq_save(flags);	if (atomic_dec_and_lock(&up->__count, &uidhash_lock))		free_user(up, flags);	else		local_irq_restore(flags);} struct user_struct *alloc_uid(struct user_namespace *ns, uid_t uid){	struct hlist_head *hashent = uidhashentry(ns, 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)			goto out_unlock; 		new->uid = uid;		atomic_set(&new->__count, 1); 		new->user_ns = get_user_ns(ns); 		/*		 * 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) {			put_user_ns(ns);			key_put(new->uid_keyring);			key_put(new->session_keyring);			kmem_cache_free(uid_cachep, new);		} else {			uid_hash_insert(new, hashent);			up = new;		}		spin_unlock_irq(&uidhash_lock);	} 	return up; out_unlock:	return NULL;} 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(init_user_ns.uidhash_table + n); 	/* Insert the root user immediately (init already runs as root) */	spin_lock_irq(&uidhash_lock);	uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0));	spin_unlock_irq(&uidhash_lock); 	return 0;} module_init(uid_cache_init);