/* * 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> /* * UID task count cache, to get fast user lookup in "alloc_uid" * when changing user ID's (ie setuid() and friends). */ #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 8)#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((uid))) static kmem_cache_t *uid_cachep;static struct list_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); struct user_struct root_user = {	.__count	= ATOMIC_INIT(1),	.processes	= ATOMIC_INIT(1),	.files		= ATOMIC_INIT(0),	.sigpending	= ATOMIC_INIT(0),	.mq_bytes	= 0,	.locked_shm     = 0,#ifdef CONFIG_KEYS	.uid_keyring	= &root_user_keyring,	.session_keyring = &root_session_keyring,#endif}; /* * These routines must be called with the uidhash spinlock held! */static inline void uid_hash_insert(struct user_struct *up, struct list_head *hashent){	list_add(&up->uidhash_list, hashent);} static inline void uid_hash_remove(struct user_struct *up){	list_del(&up->uidhash_list);} static inline struct user_struct *uid_hash_find(uid_t uid, struct list_head *hashent){	struct list_head *up; 	list_for_each(up, hashent) {		struct user_struct *user; 		user = list_entry(up, struct user_struct, uidhash_list); 		if(user->uid == uid) {			atomic_inc(&user->__count);			return user;		}	} 	return NULL;} /* * 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; 	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; 	local_irq_save(flags);	if (up && atomic_dec_and_lock(&up->__count, &uidhash_lock)) {		uid_hash_remove(up);		key_put(up->uid_keyring);		key_put(up->session_keyring);		kmem_cache_free(uid_cachep, up);		spin_unlock(&uidhash_lock);	}	local_irq_restore(flags);} struct user_struct * alloc_uid(uid_t uid){	struct list_head *hashent = uidhashentry(uid);	struct user_struct *up; 	spin_lock_irq(&uidhash_lock);	up = uid_hash_find(uid, hashent);	spin_unlock_irq(&uidhash_lock); 	if (!up) {		struct user_struct *new; 		new = kmem_cache_alloc(uid_cachep, SLAB_KERNEL);		if (!new)			return NULL;		new->uid = uid;		atomic_set(&new->__count, 1);		atomic_set(&new->processes, 0);		atomic_set(&new->files, 0);		atomic_set(&new->sigpending, 0);#ifdef CONFIG_INOTIFY		atomic_set(&new->inotify_watches, 0);		atomic_set(&new->inotify_devs, 0);#endif 		new->mq_bytes = 0;		new->locked_shm = 0; 		if (alloc_uid_keyring(new) < 0) {			kmem_cache_free(uid_cachep, new);			return NULL;		} 		/*		 * 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) {			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;} void switch_uid(struct user_struct *new_user){	struct user_struct *old_user; 	/* What if a process setreuid()'s and this brings the	 * new uid over his NPROC rlimit?  We can check this now	 * cheaply with the new uid cache, so if it matters	 * we should be checking for it.  -DaveM	 */	old_user = current->user;	atomic_inc(&new_user->processes);	atomic_dec(&old_user->processes);	switch_uid_keyring(new_user);	current->user = new_user;	free_uid(old_user);	suid_keys(current);}  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, NULL); 	for(n = 0; n < UIDHASH_SZ; ++n)		INIT_LIST_HEAD(uidhash_table + n); 	/* Insert the root user immediately (init already runs as root) */	spin_lock_irq(&uidhash_lock);	uid_hash_insert(&root_user, uidhashentry(0));	spin_unlock_irq(&uidhash_lock); 	return 0;} module_init(uid_cache_init);