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
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>
14 #define UCOUNTS_HASHTABLE_BITS 10
15 static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)];
16 static DEFINE_SPINLOCK(ucounts_lock);
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))
26 static struct ctl_table_set *
27 set_lookup(struct ctl_table_root *root)
29 return ¤t_user_ns()->set;
32 static int set_is_seen(struct ctl_table_set *set)
34 return ¤t_user_ns()->set == set;
37 static int set_permissions(struct ctl_table_header *head,
38 struct ctl_table *table)
40 struct user_namespace *user_ns =
41 container_of(head->set, struct user_namespace, set);
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;
48 /* Allow all others at most read-only access */
49 mode = table->mode & S_IROTH;
50 return (mode << 6) | (mode << 3) | mode;
53 static struct ctl_table_root set_root = {
55 .permissions = set_permissions,
59 static int int_max = INT_MAX;
60 static struct ctl_table user_table[] = {
62 .procname = "max_user_namespaces",
63 .data = &init_user_ns.max_user_namespaces,
64 .maxlen = sizeof(init_user_ns.max_user_namespaces),
66 .proc_handler = proc_dointvec_minmax,
72 #endif /* CONFIG_SYSCTL */
74 bool setup_userns_sysctls(struct user_namespace *ns)
77 struct ctl_table *tbl;
78 setup_sysctl_set(&ns->set, &set_root, set_is_seen);
79 tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL);
81 tbl[0].data = &ns->max_user_namespaces;
83 ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl);
87 retire_sysctl_set(&ns->set);
94 void retire_userns_sysctls(struct user_namespace *ns)
97 struct ctl_table *tbl;
99 tbl = ns->sysctls->ctl_table_arg;
100 unregister_sysctl_table(ns->sysctls);
101 retire_sysctl_set(&ns->set);
106 static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent)
108 struct ucounts *ucounts;
110 hlist_for_each_entry(ucounts, hashent, node) {
111 if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns))
117 static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
119 struct hlist_head *hashent = ucounts_hashentry(ns, uid);
120 struct ucounts *ucounts, *new;
122 spin_lock(&ucounts_lock);
123 ucounts = find_ucounts(ns, uid, hashent);
125 spin_unlock(&ucounts_lock);
127 new = kzalloc(sizeof(*new), GFP_KERNEL);
133 atomic_set(&new->count, 0);
135 spin_lock(&ucounts_lock);
136 ucounts = find_ucounts(ns, uid, hashent);
140 hlist_add_head(&new->node, hashent);
144 if (!atomic_add_unless(&ucounts->count, 1, INT_MAX))
146 spin_unlock(&ucounts_lock);
150 static void put_ucounts(struct ucounts *ucounts)
152 if (atomic_dec_and_test(&ucounts->count)) {
153 spin_lock(&ucounts_lock);
154 hlist_del_init(&ucounts->node);
155 spin_unlock(&ucounts_lock);
161 static inline bool atomic_inc_below(atomic_t *v, int u)
166 if (unlikely(c >= u))
168 old = atomic_cmpxchg(v, c, c+1);
169 if (likely(old == c))
175 struct ucounts *inc_user_namespaces(struct user_namespace *ns, kuid_t uid)
177 struct ucounts *ucounts, *iter, *bad;
178 struct user_namespace *tns;
179 ucounts = get_ucounts(ns, uid);
180 for (iter = ucounts; iter; iter = tns->ucounts) {
183 max = READ_ONCE(tns->max_user_namespaces);
184 if (!atomic_inc_below(&iter->user_namespaces, max))
190 for (iter = ucounts; iter != bad; iter = iter->ns->ucounts)
191 atomic_dec(&iter->user_namespaces);
193 put_ucounts(ucounts);
197 void dec_user_namespaces(struct ucounts *ucounts)
199 struct ucounts *iter;
200 for (iter = ucounts; iter; iter = iter->ns->ucounts) {
201 int dec = atomic_dec_if_positive(&iter->user_namespaces);
202 WARN_ON_ONCE(dec < 0);
204 put_ucounts(ucounts);
208 static __init int user_namespace_sysctl_init(void)
211 static struct ctl_table_header *user_header;
212 static struct ctl_table empty[1];
214 * It is necessary to register the user directory in the
215 * default set so that registrations in the child sets work
218 user_header = register_sysctl("user", empty);
219 BUG_ON(!user_header);
220 BUG_ON(!setup_userns_sysctls(&init_user_ns));
224 subsys_initcall(user_namespace_sysctl_init);