cregit-Linux how code gets into the kernel

Release 4.15 kernel/user.c

Directory: kernel
/*
 * 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_PERSISTENT_KEYRINGS
	.persistent_keyring_register_sem =
	__RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_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;

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	= ATOMIC_INIT(1),
	.processes	= ATOMIC_INIT(1),
	.sigpending	= ATOMIC_INIT(0),
	.locked_shm     = 0,
	.uid		= GLOBAL_ROOT_UID,
};

/*
 * 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); }

Contributors

PersonTokensPropCommitsCommitProp
Dhaval Giani2284.62%375.00%
Kay Sievers415.38%125.00%
Total26100.00%4100.00%


static void uid_hash_remove(struct user_struct *up) { hlist_del_init(&up->uidhash_node); }

Contributors

PersonTokensPropCommitsCommitProp
Dhaval Giani1894.74%266.67%
Srivatsa Vaddagiri15.26%133.33%
Total19100.00%3100.00%


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)) { atomic_inc(&user->__count); return user; } } return NULL; }

Contributors

PersonTokensPropCommitsCommitProp
Kay Sievers5391.38%150.00%
Eric W. Biedermann58.62%150.00%
Total58100.00%2100.00%

/* 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

Contributors

PersonTokensPropCommitsCommitProp
Dhaval Giani743.75%133.33%
Linus Torvalds (pre-git)637.50%133.33%
Namhyung Kim318.75%133.33%
Total16100.00%3100.00%

) { 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(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; }

Contributors

PersonTokensPropCommitsCommitProp
Andrew Morton3060.00%250.00%
Ingo Molnar1938.00%125.00%
Eric W. Biedermann12.00%125.00%
Total50100.00%4100.00%


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); }

Contributors

PersonTokensPropCommitsCommitProp
Linus Torvalds (pre-git)2549.02%233.33%
Andrew Morton2345.10%233.33%
Ingo Molnar23.92%116.67%
Dhaval Giani11.96%116.67%
Total51100.00%6100.00%


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) goto out_unlock; new->uid = uid; atomic_set(&new->__count, 1); /* * 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; out_unlock: return NULL; }

Contributors

PersonTokensPropCommitsCommitProp
Linus Torvalds (pre-git)12779.38%222.22%
David Howells148.75%111.11%
Pavel Emelyanov127.50%222.22%
Andrew Morton53.12%222.22%
Christoph Lameter10.62%111.11%
Eric W. Biedermann10.62%111.11%
Total160100.00%9100.00%


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; }

Contributors

PersonTokensPropCommitsCommitProp
Linus Torvalds (pre-git)4151.25%222.22%
Dave Jones2126.25%111.11%
Andrew Morton1518.75%333.33%
Eric W. Biedermann11.25%111.11%
Linus Torvalds11.25%111.11%
Pavel Emelyanov11.25%111.11%
Total80100.00%9100.00%

subsys_initcall(uid_cache_init);

Overall Contributors

PersonTokensPropCommitsCommitProp
Linus Torvalds (pre-git)25732.12%35.88%
Eric W. Biedermann14618.25%815.69%
Dhaval Giani789.75%35.88%
Andrew Morton759.38%611.76%
Kay Sievers577.12%23.92%
David Howells334.12%35.88%
Pavel Emelyanov324.00%35.88%
Dave Jones283.50%11.96%
Ingo Molnar273.38%35.88%
Al Viro162.00%23.92%
Chris Wright101.25%23.92%
Christian Brauner60.75%11.96%
Cédric Le Goater50.62%11.96%
Thomas Gleixner40.50%11.96%
Serge E. Hallyn40.50%23.92%
Namhyung Kim40.50%11.96%
Art Haas40.50%11.96%
Christoph Lameter30.38%23.92%
Rik Van Riel30.38%11.96%
Xiao Guangrong30.38%11.96%
Paul Gortmaker20.25%23.92%
Linus Torvalds20.25%11.96%
Srivatsa Vaddagiri10.12%11.96%
Total800100.00%51100.00%
Directory: kernel
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