diff options
Diffstat (limited to 'kernel/user.c')
| -rw-r--r-- | kernel/user.c | 200 |
1 files changed, 200 insertions, 0 deletions
diff --git a/kernel/user.c b/kernel/user.c new file mode 100644 index 00000000..9e03e9c1 --- /dev/null +++ b/kernel/user.c @@ -0,0 +1,200 @@ +/* + * 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); |