Release 4.13 kernel/user.c

/*
 * 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);
}

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

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3
100.00%



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;
}

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Eric W. Biedermann
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8.62%
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58
100.00%
2
100.00%

/* 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
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6
37.50%
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Namhyung Kim
3
18.75%
1
33.33%
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16
100.00%
3
100.00%

)
{
	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;
}

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2.00%
1
25.00%
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50
100.00%
4
100.00%



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);
}

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25
49.02%
2
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Andrew Morton
23
45.10%
2
33.33%
Ingo Molnar
2
3.92%
1
16.67%
Dhaval Giani
1
1.96%
1
16.67%
Total
51
100.00%
6
100.00%



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;
}

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22.22%
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14
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1
11.11%
Pavel Emelyanov
12
7.50%
2
22.22%
Andrew Morton
5
3.12%
2
22.22%
Christoph Lameter
1
0.62%
1
11.11%
Eric W. Biedermann
1
0.62%
1
11.11%
Total
160
100.00%
9
100.00%



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;
}
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11.11%
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15
18.75%
3
33.33%
Eric W. Biedermann
1
1.25%
1
11.11%
Linus Torvalds
1
1.25%
1
11.11%
Pavel Emelyanov
1
1.25%
1
11.11%
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subsys_initcall(uid_cache_init);
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18.39%
8
16.00%
Dhaval Giani
78
9.82%
3
6.00%
Andrew Morton
75
9.45%
6
12.00%
Kay Sievers
57
7.18%
2
4.00%
David Howells
33
4.16%
3
6.00%
Pavel Emelyanov
32
4.03%
3
6.00%
Dave Jones
28
3.53%
1
2.00%
Ingo Molnar
27
3.40%
3
6.00%
Al Viro
16
2.02%
2
4.00%
Chris Wright
10
1.26%
2
4.00%
Cédric Le Goater
5
0.63%
1
2.00%
Namhyung Kim
4
0.50%
1
2.00%
Thomas Gleixner
4
0.50%
1
2.00%
Art Haas
4
0.50%
1
2.00%
Serge E. Hallyn
4
0.50%
2
4.00%
Xiao Guangrong
3
0.38%
1
2.00%
Christoph Lameter
3
0.38%
2
4.00%
Rik Van Riel
3
0.38%
1
2.00%
Paul Gortmaker
2
0.25%
2
4.00%
Linus Torvalds
2
0.25%
1
2.00%
Srivatsa Vaddagiri
1
0.13%
1
2.00%
Total
794
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50
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Directory: kernel

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