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Diffstat (limited to '')
| -rw-r--r-- | kernel/user.c | 229 |
1 files changed, 229 insertions, 0 deletions
diff --git a/kernel/user.c b/kernel/user.c new file mode 100644 index 000000000..b1635d94a --- /dev/null +++ b/kernel/user.c @@ -0,0 +1,229 @@ +// 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/proc_ns.h> + +/* + * userns count is 1 for root user, 1 for init_uts_ns, + * and 1 for... ? + */ +struct user_namespace init_user_ns = { + .uid_map = { + .nr_extents = 1, + { + .extent[0] = { + .first = 0, + .lower_first = 0, + .count = 4294967295U, + }, + }, + }, + .gid_map = { + .nr_extents = 1, + { + .extent[0] = { + .first = 0, + .lower_first = 0, + .count = 4294967295U, + }, + }, + }, + .projid_map = { + .nr_extents = 1, + { + .extent[0] = { + .first = 0, + .lower_first = 0, + .count = 4294967295U, + }, + }, + }, + .count = ATOMIC_INIT(3), + .owner = GLOBAL_ROOT_UID, + .group = GLOBAL_ROOT_GID, + .ns.inum = PROC_USER_INIT_INO, +#ifdef CONFIG_USER_NS + .ns.ops = &userns_operations, +#endif + .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 +}; +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 (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), + .processes = ATOMIC_INIT(1), + .sigpending = ATOMIC_INIT(0), + .locked_shm = 0, + .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; +} + +/* 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); + 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); +} + +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); + 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) { + 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); + + /* 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); |