kernel/ucount.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2
   3 #include <linux/stat.h>
   4 #include <linux/sysctl.h>
   5 #include <linux/slab.h>
   6 #include <linux/cred.h>
   7 #include <linux/hash.h>
   8 #include <linux/kmemleak.h>
   9 #include <linux/user_namespace.h>
  10
  11 #define UCOUNTS_HASHTABLE_BITS 10
  12 static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)];
  13 static DEFINE_SPINLOCK(ucounts_lock);
  14
  15 #define ucounts_hashfn(ns, uid)                                         \
  16         hash_long((unsigned long)__kuid_val(uid) + (unsigned long)(ns), \
  17                   UCOUNTS_HASHTABLE_BITS)
  18 #define ucounts_hashentry(ns, uid)      \
  19         (ucounts_hashtable + ucounts_hashfn(ns, uid))
  20
  21
  22 #ifdef CONFIG_SYSCTL
  23 static struct ctl_table_set *
  24 set_lookup(struct ctl_table_root *root)
  25 {
  26         return &current_user_ns()->set;
  27 }
  28
  29 static int set_is_seen(struct ctl_table_set *set)
  30 {
  31         return &current_user_ns()->set == set;
  32 }
  33
  34 static int set_permissions(struct ctl_table_header *head,
  35                                   struct ctl_table *table)
  36 {
  37         struct user_namespace *user_ns =
  38                 container_of(head->set, struct user_namespace, set);
  39         int mode;
  40
  41         /* Allow users with CAP_SYS_RESOURCE unrestrained access */
  42         if (ns_capable(user_ns, CAP_SYS_RESOURCE))
  43                 mode = (table->mode & S_IRWXU) >> 6;
  44         else
  45         /* Allow all others at most read-only access */
  46                 mode = table->mode & S_IROTH;
  47         return (mode << 6) | (mode << 3) | mode;
  48 }
  49
  50 static struct ctl_table_root set_root = {
  51         .lookup = set_lookup,
  52         .permissions = set_permissions,
  53 };
  54
  55 #define UCOUNT_ENTRY(name)                              \
  56         {                                               \
  57                 .procname       = name,                 \
  58                 .maxlen         = sizeof(int),          \
  59                 .mode           = 0644,                 \
  60                 .proc_handler   = proc_dointvec_minmax, \
  61                 .extra1         = SYSCTL_ZERO,          \
  62                 .extra2         = SYSCTL_INT_MAX,       \
  63         }
  64 static struct ctl_table user_table[] = {
  65         UCOUNT_ENTRY("max_user_namespaces"),
  66         UCOUNT_ENTRY("max_pid_namespaces"),
  67         UCOUNT_ENTRY("max_uts_namespaces"),
  68         UCOUNT_ENTRY("max_ipc_namespaces"),
  69         UCOUNT_ENTRY("max_net_namespaces"),
  70         UCOUNT_ENTRY("max_mnt_namespaces"),
  71         UCOUNT_ENTRY("max_cgroup_namespaces"),
  72 #ifdef CONFIG_INOTIFY_USER
  73         UCOUNT_ENTRY("max_inotify_instances"),
  74         UCOUNT_ENTRY("max_inotify_watches"),
  75 #endif
  76         { }
  77 };
  78 #endif /* CONFIG_SYSCTL */
  79
  80 bool setup_userns_sysctls(struct user_namespace *ns)
  81 {
  82 #ifdef CONFIG_SYSCTL
  83         struct ctl_table *tbl;
  84         setup_sysctl_set(&ns->set, &set_root, set_is_seen);
  85         tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL);
  86         if (tbl) {
  87                 int i;
  88                 for (i = 0; i < UCOUNT_COUNTS; i++) {
  89                         tbl[i].data = &ns->ucount_max[i];
  90                 }
  91                 ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl);
  92         }
  93         if (!ns->sysctls) {
  94                 kfree(tbl);
  95                 retire_sysctl_set(&ns->set);
  96                 return false;
  97         }
  98 #endif
  99         return true;
 100 }
 101
 102 void retire_userns_sysctls(struct user_namespace *ns)
 103 {
 104 #ifdef CONFIG_SYSCTL
 105         struct ctl_table *tbl;
 106
 107         tbl = ns->sysctls->ctl_table_arg;
 108         unregister_sysctl_table(ns->sysctls);
 109         retire_sysctl_set(&ns->set);
 110         kfree(tbl);
 111 #endif
 112 }
 113
 114 static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent)
 115 {
 116         struct ucounts *ucounts;
 117
 118         hlist_for_each_entry(ucounts, hashent, node) {
 119                 if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns))
 120                         return ucounts;
 121         }
 122         return NULL;
 123 }
 124
 125 static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
 126 {
 127         struct hlist_head *hashent = ucounts_hashentry(ns, uid);
 128         struct ucounts *ucounts, *new;
 129
 130         spin_lock_irq(&ucounts_lock);
 131         ucounts = find_ucounts(ns, uid, hashent);
 132         if (!ucounts) {
 133                 spin_unlock_irq(&ucounts_lock);
 134
 135                 new = kzalloc(sizeof(*new), GFP_KERNEL);
 136                 if (!new)
 137                         return NULL;
 138
 139                 new->ns = ns;
 140                 new->uid = uid;
 141                 new->count = 0;
 142
 143                 spin_lock_irq(&ucounts_lock);
 144                 ucounts = find_ucounts(ns, uid, hashent);
 145                 if (ucounts) {
 146                         kfree(new);
 147                 } else {
 148                         hlist_add_head(&new->node, hashent);
 149                         ucounts = new;
 150                 }
 151         }
 152         if (ucounts->count == INT_MAX)
 153                 ucounts = NULL;
 154         else
 155                 ucounts->count += 1;
 156         spin_unlock_irq(&ucounts_lock);
 157         return ucounts;
 158 }
 159
 160 static void put_ucounts(struct ucounts *ucounts)
 161 {
 162         unsigned long flags;
 163
 164         spin_lock_irqsave(&ucounts_lock, flags);
 165         ucounts->count -= 1;
 166         if (!ucounts->count)
 167                 hlist_del_init(&ucounts->node);
 168         else
 169                 ucounts = NULL;
 170         spin_unlock_irqrestore(&ucounts_lock, flags);
 171
 172         kfree(ucounts);
 173 }
 174
 175 static inline bool atomic_inc_below(atomic_t *v, int u)
 176 {
 177         int c, old;
 178         c = atomic_read(v);
 179         for (;;) {
 180                 if (unlikely(c >= u))
 181                         return false;
 182                 old = atomic_cmpxchg(v, c, c+1);
 183                 if (likely(old == c))
 184                         return true;
 185                 c = old;
 186         }
 187 }
 188
 189 struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
 190                            enum ucount_type type)
 191 {
 192         struct ucounts *ucounts, *iter, *bad;
 193         struct user_namespace *tns;
 194         ucounts = get_ucounts(ns, uid);
 195         for (iter = ucounts; iter; iter = tns->ucounts) {
 196                 int max;
 197                 tns = iter->ns;
 198                 max = READ_ONCE(tns->ucount_max[type]);
 199                 if (!atomic_inc_below(&iter->ucount[type], max))
 200                         goto fail;
 201         }
 202         return ucounts;
 203 fail:
 204         bad = iter;
 205         for (iter = ucounts; iter != bad; iter = iter->ns->ucounts)
 206                 atomic_dec(&iter->ucount[type]);
 207
 208         put_ucounts(ucounts);
 209         return NULL;
 210 }
 211
 212 void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
 213 {
 214         struct ucounts *iter;
 215         for (iter = ucounts; iter; iter = iter->ns->ucounts) {
 216                 int dec = atomic_dec_if_positive(&iter->ucount[type]);
 217                 WARN_ON_ONCE(dec < 0);
 218         }
 219         put_ucounts(ucounts);
 220 }
 221
 222 static __init int user_namespace_sysctl_init(void)
 223 {
 224 #ifdef CONFIG_SYSCTL
 225         static struct ctl_table_header *user_header;
 226         static struct ctl_table empty[1];
 227         /*
 228          * It is necessary to register the user directory in the
 229          * default set so that registrations in the child sets work
 230          * properly.
 231          */
 232         user_header = register_sysctl("user", empty);
 233         kmemleak_ignore(user_header);
 234         BUG_ON(!user_header);
 235         BUG_ON(!setup_userns_sysctls(&init_user_ns));
 236 #endif
 237         return 0;
 238 }
 239 subsys_initcall(user_namespace_sysctl_init);