kernel/ucount.c

   1 /*
   2  *  This program is free software; you can redistribute it and/or
   3  *  modify it under the terms of the GNU General Public License as
   4  *  published by the Free Software Foundation, version 2 of the
   5  *  License.
   6  */
   7
   8 #include <linux/stat.h>
   9 #include <linux/sysctl.h>
  10 #include <linux/slab.h>
  11 #include <linux/cred.h>
  12 #include <linux/hash.h>
  13 #include <linux/kmemleak.h>
  14 #include <linux/user_namespace.h>
  15
  16 #define UCOUNTS_HASHTABLE_BITS 10
  17 static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)];
  18 static DEFINE_SPINLOCK(ucounts_lock);
  19
  20 #define ucounts_hashfn(ns, uid)                                         \
  21         hash_long((unsigned long)__kuid_val(uid) + (unsigned long)(ns), \
  22                   UCOUNTS_HASHTABLE_BITS)
  23 #define ucounts_hashentry(ns, uid)      \
  24         (ucounts_hashtable + ucounts_hashfn(ns, uid))
  25
  26
  27 #ifdef CONFIG_SYSCTL
  28 static struct ctl_table_set *
  29 set_lookup(struct ctl_table_root *root)
  30 {
  31         return &current_user_ns()->set;
  32 }
  33
  34 static int set_is_seen(struct ctl_table_set *set)
  35 {
  36         return &current_user_ns()->set == set;
  37 }
  38
  39 static int set_permissions(struct ctl_table_header *head,
  40                                   struct ctl_table *table)
  41 {
  42         struct user_namespace *user_ns =
  43                 container_of(head->set, struct user_namespace, set);
  44         int mode;
  45
  46         /* Allow users with CAP_SYS_RESOURCE unrestrained access */
  47         if (ns_capable(user_ns, CAP_SYS_RESOURCE))
  48                 mode = (table->mode & S_IRWXU) >> 6;
  49         else
  50         /* Allow all others at most read-only access */
  51                 mode = table->mode & S_IROTH;
  52         return (mode << 6) | (mode << 3) | mode;
  53 }
  54
  55 static struct ctl_table_root set_root = {
  56         .lookup = set_lookup,
  57         .permissions = set_permissions,
  58 };
  59
  60 static int zero = 0;
  61 static int int_max = INT_MAX;
  62 #define UCOUNT_ENTRY(name)                              \
  63         {                                               \
  64                 .procname       = name,                 \
  65                 .maxlen         = sizeof(int),          \
  66                 .mode           = 0644,                 \
  67                 .proc_handler   = proc_dointvec_minmax, \
  68                 .extra1         = &zero,                \
  69                 .extra2         = &int_max,             \
  70         }
  71 static struct ctl_table user_table[] = {
  72         UCOUNT_ENTRY("max_user_namespaces"),
  73         UCOUNT_ENTRY("max_pid_namespaces"),
  74         UCOUNT_ENTRY("max_uts_namespaces"),
  75         UCOUNT_ENTRY("max_ipc_namespaces"),
  76         UCOUNT_ENTRY("max_net_namespaces"),
  77         UCOUNT_ENTRY("max_mnt_namespaces"),
  78         UCOUNT_ENTRY("max_cgroup_namespaces"),
  79 #ifdef CONFIG_INOTIFY_USER
  80         UCOUNT_ENTRY("max_inotify_instances"),
  81         UCOUNT_ENTRY("max_inotify_watches"),
  82 #endif
  83         { }
  84 };
  85 #endif /* CONFIG_SYSCTL */
  86
  87 bool setup_userns_sysctls(struct user_namespace *ns)
  88 {
  89 #ifdef CONFIG_SYSCTL
  90         struct ctl_table *tbl;
  91         setup_sysctl_set(&ns->set, &set_root, set_is_seen);
  92         tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL);
  93         if (tbl) {
  94                 int i;
  95                 for (i = 0; i < UCOUNT_COUNTS; i++) {
  96                         tbl[i].data = &ns->ucount_max[i];
  97                 }
  98                 ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl);
  99         }
 100         if (!ns->sysctls) {
 101                 kfree(tbl);
 102                 retire_sysctl_set(&ns->set);
 103                 return false;
 104         }
 105 #endif
 106         return true;
 107 }
 108
 109 void retire_userns_sysctls(struct user_namespace *ns)
 110 {
 111 #ifdef CONFIG_SYSCTL
 112         struct ctl_table *tbl;
 113
 114         tbl = ns->sysctls->ctl_table_arg;
 115         unregister_sysctl_table(ns->sysctls);
 116         retire_sysctl_set(&ns->set);
 117         kfree(tbl);
 118 #endif
 119 }
 120
 121 static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent)
 122 {
 123         struct ucounts *ucounts;
 124
 125         hlist_for_each_entry(ucounts, hashent, node) {
 126                 if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns))
 127                         return ucounts;
 128         }
 129         return NULL;
 130 }
 131
 132 static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
 133 {
 134         struct hlist_head *hashent = ucounts_hashentry(ns, uid);
 135         struct ucounts *ucounts, *new;
 136
 137         spin_lock_irq(&ucounts_lock);
 138         ucounts = find_ucounts(ns, uid, hashent);
 139         if (!ucounts) {
 140                 spin_unlock_irq(&ucounts_lock);
 141
 142                 new = kzalloc(sizeof(*new), GFP_KERNEL);
 143                 if (!new)
 144                         return NULL;
 145
 146                 new->ns = ns;
 147                 new->uid = uid;
 148                 new->count = 0;
 149
 150                 spin_lock_irq(&ucounts_lock);
 151                 ucounts = find_ucounts(ns, uid, hashent);
 152                 if (ucounts) {
 153                         kfree(new);
 154                 } else {
 155                         hlist_add_head(&new->node, hashent);
 156                         ucounts = new;
 157                 }
 158         }
 159         if (ucounts->count == INT_MAX)
 160                 ucounts = NULL;
 161         else
 162                 ucounts->count += 1;
 163         spin_unlock_irq(&ucounts_lock);
 164         return ucounts;
 165 }
 166
 167 static void put_ucounts(struct ucounts *ucounts)
 168 {
 169         unsigned long flags;
 170
 171         spin_lock_irqsave(&ucounts_lock, flags);
 172         ucounts->count -= 1;
 173         if (!ucounts->count)
 174                 hlist_del_init(&ucounts->node);
 175         else
 176                 ucounts = NULL;
 177         spin_unlock_irqrestore(&ucounts_lock, flags);
 178
 179         kfree(ucounts);
 180 }
 181
 182 static inline bool atomic_inc_below(atomic_t *v, int u)
 183 {
 184         int c, old;
 185         c = atomic_read(v);
 186         for (;;) {
 187                 if (unlikely(c >= u))
 188                         return false;
 189                 old = atomic_cmpxchg(v, c, c+1);
 190                 if (likely(old == c))
 191                         return true;
 192                 c = old;
 193         }
 194 }
 195
 196 struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
 197                            enum ucount_type type)
 198 {
 199         struct ucounts *ucounts, *iter, *bad;
 200         struct user_namespace *tns;
 201         ucounts = get_ucounts(ns, uid);
 202         for (iter = ucounts; iter; iter = tns->ucounts) {
 203                 int max;
 204                 tns = iter->ns;
 205                 max = READ_ONCE(tns->ucount_max[type]);
 206                 if (!atomic_inc_below(&iter->ucount[type], max))
 207                         goto fail;
 208         }
 209         return ucounts;
 210 fail:
 211         bad = iter;
 212         for (iter = ucounts; iter != bad; iter = iter->ns->ucounts)
 213                 atomic_dec(&iter->ucount[type]);
 214
 215         put_ucounts(ucounts);
 216         return NULL;
 217 }
 218
 219 void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
 220 {
 221         struct ucounts *iter;
 222         for (iter = ucounts; iter; iter = iter->ns->ucounts) {
 223                 int dec = atomic_dec_if_positive(&iter->ucount[type]);
 224                 WARN_ON_ONCE(dec < 0);
 225         }
 226         put_ucounts(ucounts);
 227 }
 228
 229 static __init int user_namespace_sysctl_init(void)
 230 {
 231 #ifdef CONFIG_SYSCTL
 232         static struct ctl_table_header *user_header;
 233         static struct ctl_table empty[1];
 234         /*
 235          * It is necessary to register the user directory in the
 236          * default set so that registrations in the child sets work
 237          * properly.
 238          */
 239         user_header = register_sysctl("user", empty);
 240         kmemleak_ignore(user_header);
 241         BUG_ON(!user_header);
 242         BUG_ON(!setup_userns_sysctls(&init_user_ns));
 243 #endif
 244         return 0;
 245 }
 246 subsys_initcall(user_namespace_sysctl_init);