ucount.c

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