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path: root/kernel/ucount.c (plain)
blob: c761cdba2a2d816b70ee1dcb4f2c0ffcf056df43
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
15static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)];
16static 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
26static struct ctl_table_set *
27set_lookup(struct ctl_table_root *root)
28{
29 return &current_user_ns()->set;
30}
31
32static int set_is_seen(struct ctl_table_set *set)
33{
34 return &current_user_ns()->set == set;
35}
36
37static 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
53static struct ctl_table_root set_root = {
54 .lookup = set_lookup,
55 .permissions = set_permissions,
56};
57
58static int zero = 0;
59static 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 }
69static 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
81bool 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
103void 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
115static 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
126static 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 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 (ucounts->count == INT_MAX)
154 ucounts = NULL;
155 else
156 ucounts->count += 1;
157 spin_unlock_irq(&ucounts_lock);
158 return ucounts;
159}
160
161static void put_ucounts(struct ucounts *ucounts)
162{
163 unsigned long flags;
164
165 spin_lock_irqsave(&ucounts_lock, flags);
166 ucounts->count -= 1;
167 if (!ucounts->count)
168 hlist_del_init(&ucounts->node);
169 else
170 ucounts = NULL;
171 spin_unlock_irqrestore(&ucounts_lock, flags);
172
173 kfree(ucounts);
174}
175
176static inline bool atomic_inc_below(atomic_t *v, int u)
177{
178 int c, old;
179 c = atomic_read(v);
180 for (;;) {
181 if (unlikely(c >= u))
182 return false;
183 old = atomic_cmpxchg(v, c, c+1);
184 if (likely(old == c))
185 return true;
186 c = old;
187 }
188}
189
190struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
191 enum ucount_type type)
192{
193 struct ucounts *ucounts, *iter, *bad;
194 struct user_namespace *tns;
195 ucounts = get_ucounts(ns, uid);
196 for (iter = ucounts; iter; iter = tns->ucounts) {
197 int max;
198 tns = iter->ns;
199 max = READ_ONCE(tns->ucount_max[type]);
200 if (!atomic_inc_below(&iter->ucount[type], max))
201 goto fail;
202 }
203 return ucounts;
204fail:
205 bad = iter;
206 for (iter = ucounts; iter != bad; iter = iter->ns->ucounts)
207 atomic_dec(&iter->ucount[type]);
208
209 put_ucounts(ucounts);
210 return NULL;
211}
212
213void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
214{
215 struct ucounts *iter;
216 for (iter = ucounts; iter; iter = iter->ns->ucounts) {
217 int dec = atomic_dec_if_positive(&iter->ucount[type]);
218 WARN_ON_ONCE(dec < 0);
219 }
220 put_ucounts(ucounts);
221}
222
223static __init int user_namespace_sysctl_init(void)
224{
225#ifdef CONFIG_SYSCTL
226 static struct ctl_table_header *user_header;
227 static struct ctl_table empty[1];
228 /*
229 * It is necessary to register the user directory in the
230 * default set so that registrations in the child sets work
231 * properly.
232 */
233 user_header = register_sysctl("user", empty);
234 kmemleak_ignore(user_header);
235 BUG_ON(!user_header);
236 BUG_ON(!setup_userns_sysctls(&init_user_ns));
237#endif
238 return 0;
239}
240subsys_initcall(user_namespace_sysctl_init);
241
generated by cgit at 2024-05-18 16:37:39 (GMT)