1 // SPDX-License-Identifier: GPL-2.0-only
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>
11 #define UCOUNTS_HASHTABLE_BITS 10
12 static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)];
13 static DEFINE_SPINLOCK(ucounts_lock);
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))
23 static struct ctl_table_set *
24 set_lookup(struct ctl_table_root *root)
26 return ¤t_user_ns()->set;
29 static int set_is_seen(struct ctl_table_set *set)
31 return ¤t_user_ns()->set == set;
34 static int set_permissions(struct ctl_table_header *head,
35 struct ctl_table *table)
37 struct user_namespace *user_ns =
38 container_of(head->set, struct user_namespace, set);
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;
45 /* Allow all others at most read-only access */
46 mode = table->mode & S_IROTH;
47 return (mode << 6) | (mode << 3) | mode;
50 static struct ctl_table_root set_root = {
52 .permissions = set_permissions,
55 #define UCOUNT_ENTRY(name) \
58 .maxlen = sizeof(int), \
60 .proc_handler = proc_dointvec_minmax, \
61 .extra1 = SYSCTL_ZERO, \
62 .extra2 = SYSCTL_INT_MAX, \
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 UCOUNT_ENTRY("max_time_namespaces"),
73 #ifdef CONFIG_INOTIFY_USER
74 UCOUNT_ENTRY("max_inotify_instances"),
75 UCOUNT_ENTRY("max_inotify_watches"),
79 #endif /* CONFIG_SYSCTL */
81 bool setup_userns_sysctls(struct user_namespace *ns)
84 struct ctl_table *tbl;
86 BUILD_BUG_ON(ARRAY_SIZE(user_table) != UCOUNT_COUNTS + 1);
87 setup_sysctl_set(&ns->set, &set_root, set_is_seen);
88 tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL);
91 for (i = 0; i < UCOUNT_COUNTS; i++) {
92 tbl[i].data = &ns->ucount_max[i];
94 ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl);
98 retire_sysctl_set(&ns->set);
105 void retire_userns_sysctls(struct user_namespace *ns)
108 struct ctl_table *tbl;
110 tbl = ns->sysctls->ctl_table_arg;
111 unregister_sysctl_table(ns->sysctls);
112 retire_sysctl_set(&ns->set);
117 static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent)
119 struct ucounts *ucounts;
121 hlist_for_each_entry(ucounts, hashent, node) {
122 if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns))
128 static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
130 struct hlist_head *hashent = ucounts_hashentry(ns, uid);
131 struct ucounts *ucounts, *new;
133 spin_lock_irq(&ucounts_lock);
134 ucounts = find_ucounts(ns, uid, hashent);
136 spin_unlock_irq(&ucounts_lock);
138 new = kzalloc(sizeof(*new), GFP_KERNEL);
146 spin_lock_irq(&ucounts_lock);
147 ucounts = find_ucounts(ns, uid, hashent);
151 hlist_add_head(&new->node, hashent);
155 if (ucounts->count == INT_MAX)
159 spin_unlock_irq(&ucounts_lock);
163 static void put_ucounts(struct ucounts *ucounts)
167 spin_lock_irqsave(&ucounts_lock, flags);
170 hlist_del_init(&ucounts->node);
173 spin_unlock_irqrestore(&ucounts_lock, flags);
178 static inline bool atomic_inc_below(atomic_t *v, int u)
183 if (unlikely(c >= u))
185 old = atomic_cmpxchg(v, c, c+1);
186 if (likely(old == c))
192 struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
193 enum ucount_type type)
195 struct ucounts *ucounts, *iter, *bad;
196 struct user_namespace *tns;
197 ucounts = get_ucounts(ns, uid);
198 for (iter = ucounts; iter; iter = tns->ucounts) {
201 max = READ_ONCE(tns->ucount_max[type]);
202 if (!atomic_inc_below(&iter->ucount[type], max))
208 for (iter = ucounts; iter != bad; iter = iter->ns->ucounts)
209 atomic_dec(&iter->ucount[type]);
211 put_ucounts(ucounts);
215 void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
217 struct ucounts *iter;
218 for (iter = ucounts; iter; iter = iter->ns->ucounts) {
219 int dec = atomic_dec_if_positive(&iter->ucount[type]);
220 WARN_ON_ONCE(dec < 0);
222 put_ucounts(ucounts);
225 static __init int user_namespace_sysctl_init(void)
228 static struct ctl_table_header *user_header;
229 static struct ctl_table empty[1];
231 * It is necessary to register the user directory in the
232 * default set so that registrations in the child sets work
235 user_header = register_sysctl("user", empty);
236 kmemleak_ignore(user_header);
237 BUG_ON(!user_header);
238 BUG_ON(!setup_userns_sysctls(&init_user_ns));
242 subsys_initcall(user_namespace_sysctl_init);