projects/linux·blob v5.13 · refs

246 lines · 5.7 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#ifdef CONFIG_FANOTIFY
78 UCOUNT_ENTRY("max_fanotify_groups"),
79 UCOUNT_ENTRY("max_fanotify_marks"),
80#endif
81 { }
82};
83#endif /* CONFIG_SYSCTL */
84
85bool setup_userns_sysctls(struct user_namespace *ns)
86{
87#ifdef CONFIG_SYSCTL
88 struct ctl_table *tbl;
89
90 BUILD_BUG_ON(ARRAY_SIZE(user_table) != UCOUNT_COUNTS + 1);
91 setup_sysctl_set(&ns->set, &set_root, set_is_seen);
92 tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL);
93 if (tbl) {
94 int i;
95 for (i = 0; i < UCOUNT_COUNTS; i++) {
96 tbl[i].data = &ns->ucount_max[i];
97 }
98 ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl);
99 }
100 if (!ns->sysctls) {
101 kfree(tbl);
102 retire_sysctl_set(&ns->set);
103 return false;
104 }
105#endif
106 return true;
107}
108
109void retire_userns_sysctls(struct user_namespace *ns)
110{
111#ifdef CONFIG_SYSCTL
112 struct ctl_table *tbl;
113
114 tbl = ns->sysctls->ctl_table_arg;
115 unregister_sysctl_table(ns->sysctls);
116 retire_sysctl_set(&ns->set);
117 kfree(tbl);
118#endif
119}
120
121static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent)
122{
123 struct ucounts *ucounts;
124
125 hlist_for_each_entry(ucounts, hashent, node) {
126 if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns))
127 return ucounts;
128 }
129 return NULL;
130}
131
132static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
133{
134 struct hlist_head *hashent = ucounts_hashentry(ns, uid);
135 struct ucounts *ucounts, *new;
136
137 spin_lock_irq(&ucounts_lock);
138 ucounts = find_ucounts(ns, uid, hashent);
139 if (!ucounts) {
140 spin_unlock_irq(&ucounts_lock);
141
142 new = kzalloc(sizeof(*new), GFP_KERNEL);
143 if (!new)
144 return NULL;
145
146 new->ns = ns;
147 new->uid = uid;
148 new->count = 0;
149
150 spin_lock_irq(&ucounts_lock);
151 ucounts = find_ucounts(ns, uid, hashent);
152 if (ucounts) {
153 kfree(new);
154 } else {
155 hlist_add_head(&new->node, hashent);
156 ucounts = new;
157 }
158 }
159 if (ucounts->count == INT_MAX)
160 ucounts = NULL;
161 else
162 ucounts->count += 1;
163 spin_unlock_irq(&ucounts_lock);
164 return ucounts;
165}
166
167static void put_ucounts(struct ucounts *ucounts)
168{
169 unsigned long flags;
170
171 spin_lock_irqsave(&ucounts_lock, flags);
172 ucounts->count -= 1;
173 if (!ucounts->count)
174 hlist_del_init(&ucounts->node);
175 else
176 ucounts = NULL;
177 spin_unlock_irqrestore(&ucounts_lock, flags);
178
179 kfree(ucounts);
180}
181
182static inline bool atomic_inc_below(atomic_t *v, int u)
183{
184 int c, old;
185 c = atomic_read(v);
186 for (;;) {
187 if (unlikely(c >= u))
188 return false;
189 old = atomic_cmpxchg(v, c, c+1);
190 if (likely(old == c))
191 return true;
192 c = old;
193 }
194}
195
196struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
197 enum ucount_type type)
198{
199 struct ucounts *ucounts, *iter, *bad;
200 struct user_namespace *tns;
201 ucounts = get_ucounts(ns, uid);
202 for (iter = ucounts; iter; iter = tns->ucounts) {
203 int max;
204 tns = iter->ns;
205 max = READ_ONCE(tns->ucount_max[type]);
206 if (!atomic_inc_below(&iter->ucount[type], max))
207 goto fail;
208 }
209 return ucounts;
210fail:
211 bad = iter;
212 for (iter = ucounts; iter != bad; iter = iter->ns->ucounts)
213 atomic_dec(&iter->ucount[type]);
214
215 put_ucounts(ucounts);
216 return NULL;
217}
218
219void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
220{
221 struct ucounts *iter;
222 for (iter = ucounts; iter; iter = iter->ns->ucounts) {
223 int dec = atomic_dec_if_positive(&iter->ucount[type]);
224 WARN_ON_ONCE(dec < 0);
225 }
226 put_ucounts(ucounts);
227}
228
229static __init int user_namespace_sysctl_init(void)
230{
231#ifdef CONFIG_SYSCTL
232 static struct ctl_table_header *user_header;
233 static struct ctl_table empty[1];
234 /*
235 * It is necessary to register the user directory in the
236 * default set so that registrations in the child sets work
237 * properly.
238 */
239 user_header = register_sysctl("user", empty);
240 kmemleak_ignore(user_header);
241 BUG_ON(!user_header);
242 BUG_ON(!setup_userns_sysctls(&init_user_ns));
243#endif
244 return 0;
245}
246subsys_initcall(user_namespace_sysctl_init);