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 struct ucounts init_ucounts = {
12 .ns = &init_user_ns,
13 .uid = GLOBAL_ROOT_UID,
14 .count = ATOMIC_INIT(1),
15 };
16
17 #define UCOUNTS_HASHTABLE_BITS 10
18 static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)];
19 static DEFINE_SPINLOCK(ucounts_lock);
20
21 #define ucounts_hashfn(ns, uid) \
22 hash_long((unsigned long)__kuid_val(uid) + (unsigned long)(ns), \
23 UCOUNTS_HASHTABLE_BITS)
24 #define ucounts_hashentry(ns, uid) \
25 (ucounts_hashtable + ucounts_hashfn(ns, uid))
26
27
28 #ifdef CONFIG_SYSCTL
29 static struct ctl_table_set *
30 set_lookup(struct ctl_table_root *root)
31 {
32 return ¤t_user_ns()->set;
33 }
34
35 static int set_is_seen(struct ctl_table_set *set)
36 {
37 return ¤t_user_ns()->set == set;
38 }
39
40 static int set_permissions(struct ctl_table_header *head,
41 const struct ctl_table *table)
42 {
43 struct user_namespace *user_ns =
44 container_of(head->set, struct user_namespace, set);
45 int mode;
46
47 /* Allow users with CAP_SYS_RESOURCE unrestrained access */
48 if (ns_capable(user_ns, CAP_SYS_RESOURCE))
49 mode = (table->mode & S_IRWXU) >> 6;
50 else
51 /* Allow all others at most read-only access */
52 mode = table->mode & S_IROTH;
53 return (mode << 6) | (mode << 3) | mode;
54 }
55
56 static struct ctl_table_root set_root = {
57 .lookup = set_lookup,
58 .permissions = set_permissions,
59 };
60
61 static long ue_zero = 0;
62 static long ue_int_max = INT_MAX;
63
64 #define UCOUNT_ENTRY(name) \
65 { \
66 .procname = name, \
67 .maxlen = sizeof(long), \
68 .mode = 0644, \
69 .proc_handler = proc_doulongvec_minmax, \
70 .extra1 = &ue_zero, \
71 .extra2 = &ue_int_max, \
72 }
73 static struct ctl_table user_table[] = {
74 UCOUNT_ENTRY("max_user_namespaces"),
75 UCOUNT_ENTRY("max_pid_namespaces"),
76 UCOUNT_ENTRY("max_uts_namespaces"),
77 UCOUNT_ENTRY("max_ipc_namespaces"),
78 UCOUNT_ENTRY("max_net_namespaces"),
79 UCOUNT_ENTRY("max_mnt_namespaces"),
80 UCOUNT_ENTRY("max_cgroup_namespaces"),
81 UCOUNT_ENTRY("max_time_namespaces"),
82 #ifdef CONFIG_INOTIFY_USER
83 UCOUNT_ENTRY("max_inotify_instances"),
84 UCOUNT_ENTRY("max_inotify_watches"),
85 #endif
86 #ifdef CONFIG_FANOTIFY
87 UCOUNT_ENTRY("max_fanotify_groups"),
88 UCOUNT_ENTRY("max_fanotify_marks"),
89 #endif
90 };
91 #endif /* CONFIG_SYSCTL */
92
93 bool setup_userns_sysctls(struct user_namespace *ns)
94 {
95 #ifdef CONFIG_SYSCTL
96 struct ctl_table *tbl;
97
98 BUILD_BUG_ON(ARRAY_SIZE(user_table) != UCOUNT_COUNTS);
99 setup_sysctl_set(&ns->set, &set_root, set_is_seen);
100 tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL);
101 if (tbl) {
102 int i;
103 for (i = 0; i < UCOUNT_COUNTS; i++) {
104 tbl[i].data = &ns->ucount_max[i];
105 }
106 ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl,
107 ARRAY_SIZE(user_table));
108 }
109 if (!ns->sysctls) {
110 kfree(tbl);
111 retire_sysctl_set(&ns->set);
112 return false;
113 }
114 #endif
115 return true;
116 }
117
118 void retire_userns_sysctls(struct user_namespace *ns)
119 {
120 #ifdef CONFIG_SYSCTL
121 const struct ctl_table *tbl;
122
123 tbl = ns->sysctls->ctl_table_arg;
124 unregister_sysctl_table(ns->sysctls);
125 retire_sysctl_set(&ns->set);
126 kfree(tbl);
127 #endif
128 }
129
130 static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent)
131 {
132 struct ucounts *ucounts;
133
134 hlist_for_each_entry(ucounts, hashent, node) {
135 if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns))
136 return ucounts;
137 }
138 return NULL;
139 }
140
141 static void hlist_add_ucounts(struct ucounts *ucounts)
142 {
143 struct hlist_head *hashent = ucounts_hashentry(ucounts->ns, ucounts->uid);
144 spin_lock_irq(&ucounts_lock);
145 hlist_add_head(&ucounts->node, hashent);
146 spin_unlock_irq(&ucounts_lock);
147 }
148
149 static inline bool get_ucounts_or_wrap(struct ucounts *ucounts)
150 {
151 /* Returns true on a successful get, false if the count wraps. */
152 return !atomic_add_negative(1, &ucounts->count);
153 }
154
155 struct ucounts *get_ucounts(struct ucounts *ucounts)
156 {
157 if (!get_ucounts_or_wrap(ucounts)) {
158 put_ucounts(ucounts);
159 ucounts = NULL;
160 }
161 return ucounts;
162 }
163
164 struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
165 {
166 struct hlist_head *hashent = ucounts_hashentry(ns, uid);
167 struct ucounts *ucounts, *new;
168 bool wrapped;
169
170 spin_lock_irq(&ucounts_lock);
171 ucounts = find_ucounts(ns, uid, hashent);
172 if (!ucounts) {
173 spin_unlock_irq(&ucounts_lock);
174
175 new = kzalloc(sizeof(*new), GFP_KERNEL);
176 if (!new)
177 return NULL;
178
179 new->ns = ns;
180 new->uid = uid;
181 atomic_set(&new->count, 1);
182
183 spin_lock_irq(&ucounts_lock);
184 ucounts = find_ucounts(ns, uid, hashent);
185 if (ucounts) {
186 kfree(new);
187 } else {
188 hlist_add_head(&new->node, hashent);
189 get_user_ns(new->ns);
190 spin_unlock_irq(&ucounts_lock);
191 return new;
192 }
193 }
194 wrapped = !get_ucounts_or_wrap(ucounts);
195 spin_unlock_irq(&ucounts_lock);
196 if (wrapped) {
197 put_ucounts(ucounts);
198 return NULL;
199 }
200 return ucounts;
201 }
202
203 void put_ucounts(struct ucounts *ucounts)
204 {
205 unsigned long flags;
206
207 if (atomic_dec_and_lock_irqsave(&ucounts->count, &ucounts_lock, flags)) {
208 hlist_del_init(&ucounts->node);
209 spin_unlock_irqrestore(&ucounts_lock, flags);
210 put_user_ns(ucounts->ns);
211 kfree(ucounts);
212 }
213 }
214
215 static inline bool atomic_long_inc_below(atomic_long_t *v, int u)
216 {
217 long c, old;
218 c = atomic_long_read(v);
219 for (;;) {
220 if (unlikely(c >= u))
221 return false;
222 old = atomic_long_cmpxchg(v, c, c+1);
223 if (likely(old == c))
224 return true;
225 c = old;
226 }
227 }
228
229 struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
230 enum ucount_type type)
231 {
232 struct ucounts *ucounts, *iter, *bad;
233 struct user_namespace *tns;
234 ucounts = alloc_ucounts(ns, uid);
235 for (iter = ucounts; iter; iter = tns->ucounts) {
236 long max;
237 tns = iter->ns;
238 max = READ_ONCE(tns->ucount_max[type]);
239 if (!atomic_long_inc_below(&iter->ucount[type], max))
240 goto fail;
241 }
242 return ucounts;
243 fail:
244 bad = iter;
245 for (iter = ucounts; iter != bad; iter = iter->ns->ucounts)
246 atomic_long_dec(&iter->ucount[type]);
247
248 put_ucounts(ucounts);
249 return NULL;
250 }
251
252 void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
253 {
254 struct ucounts *iter;
255 for (iter = ucounts; iter; iter = iter->ns->ucounts) {
256 long dec = atomic_long_dec_if_positive(&iter->ucount[type]);
257 WARN_ON_ONCE(dec < 0);
258 }
259 put_ucounts(ucounts);
260 }
261
262 long inc_rlimit_ucounts(struct ucounts *ucounts, enum rlimit_type type, long v)
263 {
264 struct ucounts *iter;
265 long max = LONG_MAX;
266 long ret = 0;
267
268 for (iter = ucounts; iter; iter = iter->ns->ucounts) {
269 long new = atomic_long_add_return(v, &iter->rlimit[type]);
270 if (new < 0 || new > max)
271 ret = LONG_MAX;
272 else if (iter == ucounts)
273 ret = new;
274 max = get_userns_rlimit_max(iter->ns, type);
275 }
276 return ret;
277 }
278
279 bool dec_rlimit_ucounts(struct ucounts *ucounts, enum rlimit_type type, long v)
280 {
281 struct ucounts *iter;
282 long new = -1; /* Silence compiler warning */
283 for (iter = ucounts; iter; iter = iter->ns->ucounts) {
284 long dec = atomic_long_sub_return(v, &iter->rlimit[type]);
285 WARN_ON_ONCE(dec < 0);
286 if (iter == ucounts)
287 new = dec;
288 }
289 return (new == 0);
290 }
291
292 static void do_dec_rlimit_put_ucounts(struct ucounts *ucounts,
293 struct ucounts *last, enum rlimit_type type)
294 {
295 struct ucounts *iter, *next;
296 for (iter = ucounts; iter != last; iter = next) {
297 long dec = atomic_long_sub_return(1, &iter->rlimit[type]);
298 WARN_ON_ONCE(dec < 0);
299 next = iter->ns->ucounts;
300 if (dec == 0)
301 put_ucounts(iter);
302 }
303 }
304
305 void dec_rlimit_put_ucounts(struct ucounts *ucounts, enum rlimit_type type)
306 {
307 do_dec_rlimit_put_ucounts(ucounts, NULL, type);
308 }
309
310 long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum rlimit_type type)
311 {
312 /* Caller must hold a reference to ucounts */
313 struct ucounts *iter;
314 long max = LONG_MAX;
315 long dec, ret = 0;
316
317 for (iter = ucounts; iter; iter = iter->ns->ucounts) {
318 long new = atomic_long_add_return(1, &iter->rlimit[type]);
319 if (new < 0 || new > max)
320 goto unwind;
321 if (iter == ucounts)
322 ret = new;
323 max = get_userns_rlimit_max(iter->ns, type);
324 /*
325 * Grab an extra ucount reference for the caller when
326 * the rlimit count was previously 0.
327 */
328 if (new != 1)
329 continue;
330 if (!get_ucounts(iter))
331 goto dec_unwind;
332 }
333 return ret;
334 dec_unwind:
335 dec = atomic_long_sub_return(1, &iter->rlimit[type]);
336 WARN_ON_ONCE(dec < 0);
337 unwind:
338 do_dec_rlimit_put_ucounts(ucounts, iter, type);
339 return 0;
340 }
341
342 bool is_rlimit_overlimit(struct ucounts *ucounts, enum rlimit_type type, unsigned long rlimit)
343 {
344 struct ucounts *iter;
345 long max = rlimit;
346 if (rlimit > LONG_MAX)
347 max = LONG_MAX;
348 for (iter = ucounts; iter; iter = iter->ns->ucounts) {
349 long val = get_rlimit_value(iter, type);
350 if (val < 0 || val > max)
351 return true;
352 max = get_userns_rlimit_max(iter->ns, type);
353 }
354 return false;
355 }
356
357 static __init int user_namespace_sysctl_init(void)
358 {
359 #ifdef CONFIG_SYSCTL
360 static struct ctl_table_header *user_header;
361 static struct ctl_table empty[1];
362 /*
363 * It is necessary to register the user directory in the
364 * default set so that registrations in the child sets work
365 * properly.
366 */
367 user_header = register_sysctl_sz("user", empty, 0);
368 kmemleak_ignore(user_header);
369 BUG_ON(!user_header);
370 BUG_ON(!setup_userns_sysctls(&init_user_ns));
371 #endif
372 hlist_add_ucounts(&init_ucounts);
373 inc_rlimit_ucounts(&init_ucounts, UCOUNT_RLIMIT_NPROC, 1);
374 return 0;
375 }
376 subsys_initcall(user_namespace_sysctl_init);
377
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.