1 /* 2 * The "user cache". 3 * 4 * (C) Copyright 1991-2000 Linus Torvalds 5 * 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. 9 */ 10 11 #include <linux/init.h> 12 #include <linux/sched.h> 13 #include <linux/slab.h> 14 #include <linux/bitops.h> 15 #include <linux/key.h> 16 #include <linux/interrupt.h> 17 #include <linux/module.h> 18 #include <linux/user_namespace.h> 19 20 /* 21 * UID task count cache, to get fast user lookup in "alloc_uid" 22 * when changing user ID's (ie setuid() and friends). 23 */ 24 25 #define UIDHASH_MASK (UIDHASH_SZ - 1) 26 #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK) 27 #define uidhashentry(ns, uid) ((ns)->uidhash_table + __uidhashfn((uid))) 28 29 static struct kmem_cache *uid_cachep; 30 31 /* 32 * The uidhash_lock is mostly taken from process context, but it is 33 * occasionally also taken from softirq/tasklet context, when 34 * task-structs get RCU-freed. Hence all locking must be softirq-safe. 35 * But free_uid() is also called with local interrupts disabled, and running 36 * local_bh_enable() with local interrupts disabled is an error - we'll run 37 * softirq callbacks, and they can unconditionally enable interrupts, and 38 * the caller of free_uid() didn't expect that.. 39 */ 40 static DEFINE_SPINLOCK(uidhash_lock); 41 42 struct user_struct root_user = { 43 .__count = ATOMIC_INIT(1), 44 .processes = ATOMIC_INIT(1), 45 .files = ATOMIC_INIT(0), 46 .sigpending = ATOMIC_INIT(0), 47 .mq_bytes = 0, 48 .locked_shm = 0, 49 #ifdef CONFIG_KEYS 50 .uid_keyring = &root_user_keyring, 51 .session_keyring = &root_session_keyring, 52 #endif 53 }; 54 55 /* 56 * These routines must be called with the uidhash spinlock held! 57 */ 58 static inline void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent) 59 { 60 hlist_add_head(&up->uidhash_node, hashent); 61 } 62 63 static inline void uid_hash_remove(struct user_struct *up) 64 { 65 hlist_del_init(&up->uidhash_node); 66 } 67 68 static inline struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent) 69 { 70 struct user_struct *user; 71 struct hlist_node *h; 72 73 hlist_for_each_entry(user, h, hashent, uidhash_node) { 74 if(user->uid == uid) { 75 atomic_inc(&user->__count); 76 return user; 77 } 78 } 79 80 return NULL; 81 } 82 83 /* 84 * Locate the user_struct for the passed UID. If found, take a ref on it. The 85 * caller must undo that ref with free_uid(). 86 * 87 * If the user_struct could not be found, return NULL. 88 */ 89 struct user_struct *find_user(uid_t uid) 90 { 91 struct user_struct *ret; 92 unsigned long flags; 93 struct user_namespace *ns = current->nsproxy->user_ns; 94 95 spin_lock_irqsave(&uidhash_lock, flags); 96 ret = uid_hash_find(uid, uidhashentry(ns, uid)); 97 spin_unlock_irqrestore(&uidhash_lock, flags); 98 return ret; 99 } 100 101 void free_uid(struct user_struct *up) 102 { 103 unsigned long flags; 104 105 if (!up) 106 return; 107 108 local_irq_save(flags); 109 if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) { 110 uid_hash_remove(up); 111 spin_unlock_irqrestore(&uidhash_lock, flags); 112 key_put(up->uid_keyring); 113 key_put(up->session_keyring); 114 kmem_cache_free(uid_cachep, up); 115 } else { 116 local_irq_restore(flags); 117 } 118 } 119 120 struct user_struct * alloc_uid(struct user_namespace *ns, uid_t uid) 121 { 122 struct hlist_head *hashent = uidhashentry(ns, uid); 123 struct user_struct *up; 124 125 spin_lock_irq(&uidhash_lock); 126 up = uid_hash_find(uid, hashent); 127 spin_unlock_irq(&uidhash_lock); 128 129 if (!up) { 130 struct user_struct *new; 131 132 new = kmem_cache_alloc(uid_cachep, GFP_KERNEL); 133 if (!new) 134 return NULL; 135 new->uid = uid; 136 atomic_set(&new->__count, 1); 137 atomic_set(&new->processes, 0); 138 atomic_set(&new->files, 0); 139 atomic_set(&new->sigpending, 0); 140 #ifdef CONFIG_INOTIFY_USER 141 atomic_set(&new->inotify_watches, 0); 142 atomic_set(&new->inotify_devs, 0); 143 #endif 144 145 new->mq_bytes = 0; 146 new->locked_shm = 0; 147 148 if (alloc_uid_keyring(new, current) < 0) { 149 kmem_cache_free(uid_cachep, new); 150 return NULL; 151 } 152 153 /* 154 * Before adding this, check whether we raced 155 * on adding the same user already.. 156 */ 157 spin_lock_irq(&uidhash_lock); 158 up = uid_hash_find(uid, hashent); 159 if (up) { 160 key_put(new->uid_keyring); 161 key_put(new->session_keyring); 162 kmem_cache_free(uid_cachep, new); 163 } else { 164 uid_hash_insert(new, hashent); 165 up = new; 166 } 167 spin_unlock_irq(&uidhash_lock); 168 169 } 170 return up; 171 } 172 173 void switch_uid(struct user_struct *new_user) 174 { 175 struct user_struct *old_user; 176 177 /* What if a process setreuid()'s and this brings the 178 * new uid over his NPROC rlimit? We can check this now 179 * cheaply with the new uid cache, so if it matters 180 * we should be checking for it. -DaveM 181 */ 182 old_user = current->user; 183 atomic_inc(&new_user->processes); 184 atomic_dec(&old_user->processes); 185 switch_uid_keyring(new_user); 186 current->user = new_user; 187 188 /* 189 * We need to synchronize with __sigqueue_alloc() 190 * doing a get_uid(p->user).. If that saw the old 191 * user value, we need to wait until it has exited 192 * its critical region before we can free the old 193 * structure. 194 */ 195 smp_mb(); 196 spin_unlock_wait(¤t->sighand->siglock); 197 198 free_uid(old_user); 199 suid_keys(current); 200 } 201 202 void release_uids(struct user_namespace *ns) 203 { 204 int i; 205 unsigned long flags; 206 struct hlist_head *head; 207 struct hlist_node *nd; 208 209 spin_lock_irqsave(&uidhash_lock, flags); 210 /* 211 * collapse the chains so that the user_struct-s will 212 * be still alive, but not in hashes. subsequent free_uid() 213 * will free them. 214 */ 215 for (i = 0; i < UIDHASH_SZ; i++) { 216 head = ns->uidhash_table + i; 217 while (!hlist_empty(head)) { 218 nd = head->first; 219 hlist_del_init(nd); 220 } 221 } 222 spin_unlock_irqrestore(&uidhash_lock, flags); 223 224 free_uid(ns->root_user); 225 } 226 227 static int __init uid_cache_init(void) 228 { 229 int n; 230 231 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct), 232 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); 233 234 for(n = 0; n < UIDHASH_SZ; ++n) 235 INIT_HLIST_HEAD(init_user_ns.uidhash_table + n); 236 237 /* Insert the root user immediately (init already runs as root) */ 238 spin_lock_irq(&uidhash_lock); 239 uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0)); 240 spin_unlock_irq(&uidhash_lock); 241 242 return 0; 243 } 244 245 module_init(uid_cache_init); 246