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
11struct 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
18static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)];
19static 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
29static struct ctl_table_set *
30set_lookup(struct ctl_table_root *root)
31{
32	return &current_user_ns()->set;
33}
34
35static int set_is_seen(struct ctl_table_set *set)
36{
37	return &current_user_ns()->set == set;
38}
39
40static 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
56static struct ctl_table_root set_root = {
57	.lookup = set_lookup,
58	.permissions = set_permissions,
59};
60
61static long ue_zero = 0;
62static 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	}
73static 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
93bool 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
118void 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
130static 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
141static 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
149static 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
155struct 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
164struct 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
203void 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
215static 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
229struct 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;
243fail:
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
252void 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
262long 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
279bool 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
292static 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
305void dec_rlimit_put_ucounts(struct ucounts *ucounts, enum rlimit_type type)
306{
307	do_dec_rlimit_put_ucounts(ucounts, NULL, type);
308}
309
310long 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;
334dec_unwind:
335	dec = atomic_long_sub_return(1, &iter->rlimit[type]);
336	WARN_ON_ONCE(dec < 0);
337unwind:
338	do_dec_rlimit_put_ucounts(ucounts, iter, type);
339	return 0;
340}
341
342bool 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
357static __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}
376subsys_initcall(user_namespace_sysctl_init);
377