Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

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

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