/* * 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; if (!up) return; local_irq_save(flags); if (atomic_dec_and_lock(&up->__count, &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); } else { 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);