projects/linux·blob v5.12 · refs

242 lines · 5.6 KiB

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
12static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)];
13static 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
23static struct ctl_table_set *
24set_lookup(struct ctl_table_root *root)
25{
26 return &current_user_ns()->set;
27}
28
29static int set_is_seen(struct ctl_table_set *set)
30{
31 return &current_user_ns()->set == set;
32}
33
34static 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
50static 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 }
64static 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"),
76#endif
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
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);
89 if (tbl) {
90 int i;
91 for (i = 0; i < UCOUNT_COUNTS; i++) {
92 tbl[i].data = &ns->ucount_max[i];
93 }
94 ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl);
95 }
96 if (!ns->sysctls) {
97 kfree(tbl);
98 retire_sysctl_set(&ns->set);
99 return false;
100 }
101#endif
102 return true;
103}
104
105void retire_userns_sysctls(struct user_namespace *ns)
106{
107#ifdef CONFIG_SYSCTL
108 struct ctl_table *tbl;
109
110 tbl = ns->sysctls->ctl_table_arg;
111 unregister_sysctl_table(ns->sysctls);
112 retire_sysctl_set(&ns->set);
113 kfree(tbl);
114#endif
115}
116
117static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent)
118{
119 struct ucounts *ucounts;
120
121 hlist_for_each_entry(ucounts, hashent, node) {
122 if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns))
123 return ucounts;
124 }
125 return NULL;
126}
127
128static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
129{
130 struct hlist_head *hashent = ucounts_hashentry(ns, uid);
131 struct ucounts *ucounts, *new;
132
133 spin_lock_irq(&ucounts_lock);
134 ucounts = find_ucounts(ns, uid, hashent);
135 if (!ucounts) {
136 spin_unlock_irq(&ucounts_lock);
137
138 new = kzalloc(sizeof(*new), GFP_KERNEL);
139 if (!new)
140 return NULL;
141
142 new->ns = ns;
143 new->uid = uid;
144 new->count = 0;
145
146 spin_lock_irq(&ucounts_lock);
147 ucounts = find_ucounts(ns, uid, hashent);
148 if (ucounts) {
149 kfree(new);
150 } else {
151 hlist_add_head(&new->node, hashent);
152 ucounts = new;
153 }
154 }
155 if (ucounts->count == INT_MAX)
156 ucounts = NULL;
157 else
158 ucounts->count += 1;
159 spin_unlock_irq(&ucounts_lock);
160 return ucounts;
161}
162
163static void put_ucounts(struct ucounts *ucounts)
164{
165 unsigned long flags;
166
167 spin_lock_irqsave(&ucounts_lock, flags);
168 ucounts->count -= 1;
169 if (!ucounts->count)
170 hlist_del_init(&ucounts->node);
171 else
172 ucounts = NULL;
173 spin_unlock_irqrestore(&ucounts_lock, flags);
174
175 kfree(ucounts);
176}
177
178static inline bool atomic_inc_below(atomic_t *v, int u)
179{
180 int c, old;
181 c = atomic_read(v);
182 for (;;) {
183 if (unlikely(c >= u))
184 return false;
185 old = atomic_cmpxchg(v, c, c+1);
186 if (likely(old == c))
187 return true;
188 c = old;
189 }
190}
191
192struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
193 enum ucount_type type)
194{
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) {
199 int max;
200 tns = iter->ns;
201 max = READ_ONCE(tns->ucount_max[type]);
202 if (!atomic_inc_below(&iter->ucount[type], max))
203 goto fail;
204 }
205 return ucounts;
206fail:
207 bad = iter;
208 for (iter = ucounts; iter != bad; iter = iter->ns->ucounts)
209 atomic_dec(&iter->ucount[type]);
210
211 put_ucounts(ucounts);
212 return NULL;
213}
214
215void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
216{
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);
221 }
222 put_ucounts(ucounts);
223}
224
225static __init int user_namespace_sysctl_init(void)
226{
227#ifdef CONFIG_SYSCTL
228 static struct ctl_table_header *user_header;
229 static struct ctl_table empty[1];
230 /*
231 * It is necessary to register the user directory in the
232 * default set so that registrations in the child sets work
233 * properly.
234 */
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));
239#endif
240 return 0;
241}
242subsys_initcall(user_namespace_sysctl_init);