kernel/user.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * The "user cache".
   4  *
   5  * (C) Copyright 1991-2000 Linus Torvalds
   6  *
   7  * We have a per-user structure to keep track of how many
   8  * processes, files etc the user has claimed, in order to be
   9  * able to have per-user limits for system resources.
  10  */
  11
  12 #include <linux/init.h>
  13 #include <linux/sched.h>
  14 #include <linux/slab.h>
  15 #include <linux/bitops.h>
  16 #include <linux/key.h>
  17 #include <linux/sched/user.h>
  18 #include <linux/interrupt.h>
  19 #include <linux/export.h>
  20 #include <linux/user_namespace.h>
  21 #include <linux/binfmts.h>
  22 #include <linux/proc_ns.h>
  23
  24 #if IS_ENABLED(CONFIG_BINFMT_MISC)
  25 struct binfmt_misc init_binfmt_misc = {
  26         .entries = LIST_HEAD_INIT(init_binfmt_misc.entries),
  27         .enabled = true,
  28         .entries_lock = __RW_LOCK_UNLOCKED(init_binfmt_misc.entries_lock),
  29 };
  30 EXPORT_SYMBOL_GPL(init_binfmt_misc);
  31 #endif
  32
  33 /*
  34  * userns count is 1 for root user, 1 for init_uts_ns,
  35  * and 1 for... ?
  36  */
  37 struct user_namespace init_user_ns = {
  38         .uid_map = {
  39                 {
  40                         .extent[0] = {
  41                                 .first = 0,
  42                                 .lower_first = 0,
  43                                 .count = 4294967295U,
  44                         },
  45                         .nr_extents = 1,
  46                 },
  47         },
  48         .gid_map = {
  49                 {
  50                         .extent[0] = {
  51                                 .first = 0,
  52                                 .lower_first = 0,
  53                                 .count = 4294967295U,
  54                         },
  55                         .nr_extents = 1,
  56                 },
  57         },
  58         .projid_map = {
  59                 {
  60                         .extent[0] = {
  61                                 .first = 0,
  62                                 .lower_first = 0,
  63                                 .count = 4294967295U,
  64                         },
  65                         .nr_extents = 1,
  66                 },
  67         },
  68         .ns.count = REFCOUNT_INIT(3),
  69         .owner = GLOBAL_ROOT_UID,
  70         .group = GLOBAL_ROOT_GID,
  71         .ns.inum = PROC_USER_INIT_INO,
  72 #ifdef CONFIG_USER_NS
  73         .ns.ops = &userns_operations,
  74 #endif
  75         .flags = USERNS_INIT_FLAGS,
  76 #ifdef CONFIG_KEYS
  77         .keyring_name_list = LIST_HEAD_INIT(init_user_ns.keyring_name_list),
  78         .keyring_sem = __RWSEM_INITIALIZER(init_user_ns.keyring_sem),
  79 #endif
  80 #if IS_ENABLED(CONFIG_BINFMT_MISC)
  81         .binfmt_misc = &init_binfmt_misc,
  82 #endif
  83 };
  84 EXPORT_SYMBOL_GPL(init_user_ns);
  85
  86 /*
  87  * UID task count cache, to get fast user lookup in "alloc_uid"
  88  * when changing user ID's (ie setuid() and friends).
  89  */
  90
  91 #define UIDHASH_BITS    (IS_ENABLED(CONFIG_BASE_SMALL) ? 3 : 7)
  92 #define UIDHASH_SZ      (1 << UIDHASH_BITS)
  93 #define UIDHASH_MASK            (UIDHASH_SZ - 1)
  94 #define __uidhashfn(uid)        (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
  95 #define uidhashentry(uid)       (uidhash_table + __uidhashfn((__kuid_val(uid))))
  96
  97 static struct kmem_cache *uid_cachep;
  98 static struct hlist_head uidhash_table[UIDHASH_SZ];
  99
 100 /*
 101  * The uidhash_lock is mostly taken from process context, but it is
 102  * occasionally also taken from softirq/tasklet context, when
 103  * task-structs get RCU-freed. Hence all locking must be softirq-safe.
 104  * But free_uid() is also called with local interrupts disabled, and running
 105  * local_bh_enable() with local interrupts disabled is an error - we'll run
 106  * softirq callbacks, and they can unconditionally enable interrupts, and
 107  * the caller of free_uid() didn't expect that..
 108  */
 109 static DEFINE_SPINLOCK(uidhash_lock);
 110
 111 /* root_user.__count is 1, for init task cred */
 112 struct user_struct root_user = {
 113         .__count        = REFCOUNT_INIT(1),
 114         .uid            = GLOBAL_ROOT_UID,
 115         .ratelimit      = RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0),
 116 };
 117
 118 /*
 119  * These routines must be called with the uidhash spinlock held!
 120  */
 121 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
 122 {
 123         hlist_add_head(&up->uidhash_node, hashent);
 124 }
 125
 126 static void uid_hash_remove(struct user_struct *up)
 127 {
 128         hlist_del_init(&up->uidhash_node);
 129 }
 130
 131 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
 132 {
 133         struct user_struct *user;
 134
 135         hlist_for_each_entry(user, hashent, uidhash_node) {
 136                 if (uid_eq(user->uid, uid)) {
 137                         refcount_inc(&user->__count);
 138                         return user;
 139                 }
 140         }
 141
 142         return NULL;
 143 }
 144
 145 static int user_epoll_alloc(struct user_struct *up)
 146 {
 147 #ifdef CONFIG_EPOLL
 148         return percpu_counter_init(&up->epoll_watches, 0, GFP_KERNEL);
 149 #else
 150         return 0;
 151 #endif
 152 }
 153
 154 static void user_epoll_free(struct user_struct *up)
 155 {
 156 #ifdef CONFIG_EPOLL
 157         percpu_counter_destroy(&up->epoll_watches);
 158 #endif
 159 }
 160
 161 /* IRQs are disabled and uidhash_lock is held upon function entry.
 162  * IRQ state (as stored in flags) is restored and uidhash_lock released
 163  * upon function exit.
 164  */
 165 static void free_user(struct user_struct *up, unsigned long flags)
 166         __releases(&uidhash_lock)
 167 {
 168         uid_hash_remove(up);
 169         spin_unlock_irqrestore(&uidhash_lock, flags);
 170         user_epoll_free(up);
 171         kmem_cache_free(uid_cachep, up);
 172 }
 173
 174 /*
 175  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
 176  * caller must undo that ref with free_uid().
 177  *
 178  * If the user_struct could not be found, return NULL.
 179  */
 180 struct user_struct *find_user(kuid_t uid)
 181 {
 182         struct user_struct *ret;
 183         unsigned long flags;
 184
 185         spin_lock_irqsave(&uidhash_lock, flags);
 186         ret = uid_hash_find(uid, uidhashentry(uid));
 187         spin_unlock_irqrestore(&uidhash_lock, flags);
 188         return ret;
 189 }
 190
 191 void free_uid(struct user_struct *up)
 192 {
 193         unsigned long flags;
 194
 195         if (!up)
 196                 return;
 197
 198         if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))
 199                 free_user(up, flags);
 200 }
 201 EXPORT_SYMBOL_GPL(free_uid);
 202
 203 struct user_struct *alloc_uid(kuid_t uid)
 204 {
 205         struct hlist_head *hashent = uidhashentry(uid);
 206         struct user_struct *up, *new;
 207
 208         spin_lock_irq(&uidhash_lock);
 209         up = uid_hash_find(uid, hashent);
 210         spin_unlock_irq(&uidhash_lock);
 211
 212         if (!up) {
 213                 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
 214                 if (!new)
 215                         return NULL;
 216
 217                 new->uid = uid;
 218                 refcount_set(&new->__count, 1);
 219                 if (user_epoll_alloc(new)) {
 220                         kmem_cache_free(uid_cachep, new);
 221                         return NULL;
 222                 }
 223                 ratelimit_state_init(&new->ratelimit, HZ, 100);
 224                 ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE);
 225
 226                 /*
 227                  * Before adding this, check whether we raced
 228                  * on adding the same user already..
 229                  */
 230                 spin_lock_irq(&uidhash_lock);
 231                 up = uid_hash_find(uid, hashent);
 232                 if (up) {
 233                         user_epoll_free(new);
 234                         kmem_cache_free(uid_cachep, new);
 235                 } else {
 236                         uid_hash_insert(new, hashent);
 237                         up = new;
 238                 }
 239                 spin_unlock_irq(&uidhash_lock);
 240         }
 241
 242         return up;
 243 }
 244
 245 static int __init uid_cache_init(void)
 246 {
 247         int n;
 248
 249         uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
 250                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 251
 252         for(n = 0; n < UIDHASH_SZ; ++n)
 253                 INIT_HLIST_HEAD(uidhash_table + n);
 254
 255         if (user_epoll_alloc(&root_user))
 256                 panic("root_user epoll percpu counter alloc failed");
 257
 258         /* Insert the root user immediately (init already runs as root) */
 259         spin_lock_irq(&uidhash_lock);
 260         uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
 261         spin_unlock_irq(&uidhash_lock);
 262
 263         return 0;
 264 }
 265 subsys_initcall(uid_cache_init);