4 * (C) Copyright 1991-2000 Linus Torvalds
6 * We have a per-user structure to keep track of how many
7 * processes, files etc the user has claimed, in order to be
8 * able to have per-user limits for system resources.
11 #include <linux/init.h>
12 #include <linux/sched.h>
13 #include <linux/slab.h>
14 #include <linux/bitops.h>
17 * UID task count cache, to get fast user lookup in "alloc_uid"
18 * when changing user ID's (ie setuid() and friends).
20 #define UIDHASH_BITS 8
21 #define UIDHASH_SZ (1 << UIDHASH_BITS)
22 #define UIDHASH_MASK (UIDHASH_SZ - 1)
23 #define __uidhashfn(xid,uid) ((((uid) >> UIDHASH_BITS) + ((uid)^(xid))) & UIDHASH_MASK)
24 #define uidhashentry(xid,uid) (uidhash_table + __uidhashfn((xid),(uid)))
26 static kmem_cache_t *uid_cachep;
27 static struct list_head uidhash_table[UIDHASH_SZ];
28 static spinlock_t uidhash_lock = SPIN_LOCK_UNLOCKED;
30 struct user_struct root_user = {
31 .__count = ATOMIC_INIT(1),
32 .processes = ATOMIC_INIT(1),
33 .files = ATOMIC_INIT(0)
37 * These routines must be called with the uidhash spinlock held!
39 static inline void uid_hash_insert(struct user_struct *up, struct list_head *hashent)
41 list_add(&up->uidhash_list, hashent);
44 static inline void uid_hash_remove(struct user_struct *up)
46 list_del(&up->uidhash_list);
49 static inline struct user_struct *uid_hash_find(xid_t xid, uid_t uid, struct list_head *hashent)
53 list_for_each(up, hashent) {
54 struct user_struct *user;
56 user = list_entry(up, struct user_struct, uidhash_list);
58 if(user->uid == uid && user->xid == xid) {
59 atomic_inc(&user->__count);
67 struct user_struct *find_user(xid_t xid, uid_t uid)
69 return uid_hash_find(xid, uid, uidhashentry(xid, uid));
72 void free_uid(struct user_struct *up)
74 if (up && atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
76 kmem_cache_free(uid_cachep, up);
77 spin_unlock(&uidhash_lock);
81 struct user_struct * alloc_uid(xid_t xid, uid_t uid)
83 struct list_head *hashent = uidhashentry(xid, uid);
84 struct user_struct *up;
86 spin_lock(&uidhash_lock);
87 up = uid_hash_find(xid, uid, hashent);
88 spin_unlock(&uidhash_lock);
91 struct user_struct *new;
93 new = kmem_cache_alloc(uid_cachep, SLAB_KERNEL);
98 atomic_set(&new->__count, 1);
99 atomic_set(&new->processes, 0);
100 atomic_set(&new->files, 0);
103 * Before adding this, check whether we raced
104 * on adding the same user already..
106 spin_lock(&uidhash_lock);
107 up = uid_hash_find(xid, uid, hashent);
109 kmem_cache_free(uid_cachep, new);
111 uid_hash_insert(new, hashent);
114 spin_unlock(&uidhash_lock);
120 void switch_uid(struct user_struct *new_user)
122 struct user_struct *old_user;
124 /* What if a process setreuid()'s and this brings the
125 * new uid over his NPROC rlimit? We can check this now
126 * cheaply with the new uid cache, so if it matters
127 * we should be checking for it. -DaveM
129 old_user = current->user;
130 atomic_inc(&new_user->processes);
131 atomic_dec(&old_user->processes);
132 current->user = new_user;
137 static int __init uid_cache_init(void)
141 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
143 SLAB_HWCACHE_ALIGN, NULL, NULL);
145 panic("Cannot create uid taskcount SLAB cache\n");
147 for(n = 0; n < UIDHASH_SZ; ++n)
148 INIT_LIST_HEAD(uidhash_table + n);
150 /* Insert the root user immediately (init already runs as root) */
151 spin_lock(&uidhash_lock);
152 uid_hash_insert(&root_user, uidhashentry(0,0));
153 spin_unlock(&uidhash_lock);
158 module_init(uid_cache_init);