1/*
  2 *  This program is free software; you can redistribute it and/or
  3 *  modify it under the terms of the GNU General Public License as
  4 *  published by the Free Software Foundation, version 2 of the
  5 *  License.
  6 */
  7
  8#include <linux/stat.h>
  9#include <linux/sysctl.h>
 10#include <linux/slab.h>
 11#include <linux/hash.h>
 12#include <linux/user_namespace.h>
 13
 14#define UCOUNTS_HASHTABLE_BITS 10
 15static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)];
 16static DEFINE_SPINLOCK(ucounts_lock);
 17
 18#define ucounts_hashfn(ns, uid)						\
 19	hash_long((unsigned long)__kuid_val(uid) + (unsigned long)(ns), \
 20		  UCOUNTS_HASHTABLE_BITS)
 21#define ucounts_hashentry(ns, uid)	\
 22	(ucounts_hashtable + ucounts_hashfn(ns, uid))
 23
 24
 25#ifdef CONFIG_SYSCTL
 26static struct ctl_table_set *
 27set_lookup(struct ctl_table_root *root)
 28{
 29	return &current_user_ns()->set;
 30}
 31
 32static int set_is_seen(struct ctl_table_set *set)
 33{
 34	return &current_user_ns()->set == set;
 35}
 36
 37static int set_permissions(struct ctl_table_header *head,
 38				  struct ctl_table *table)
 39{
 40	struct user_namespace *user_ns =
 41		container_of(head->set, struct user_namespace, set);
 42	int mode;
 43
 44	/* Allow users with CAP_SYS_RESOURCE unrestrained access */
 45	if (ns_capable(user_ns, CAP_SYS_RESOURCE))
 46		mode = (table->mode & S_IRWXU) >> 6;
 47	else
 48	/* Allow all others at most read-only access */
 49		mode = table->mode & S_IROTH;
 50	return (mode << 6) | (mode << 3) | mode;
 51}
 52
 53static struct ctl_table_root set_root = {
 54	.lookup = set_lookup,
 55	.permissions = set_permissions,
 56};
 57
 58static int zero = 0;
 59static int int_max = INT_MAX;
 60#define UCOUNT_ENTRY(name) 				\
 61	{						\
 62		.procname	= name,			\
 63		.maxlen		= sizeof(int),		\
 64		.mode		= 0644,			\
 65		.proc_handler	= proc_dointvec_minmax,	\
 66		.extra1		= &zero,		\
 67		.extra2		= &int_max,		\
 68	}
 69static struct ctl_table user_table[] = {
 70	UCOUNT_ENTRY("max_user_namespaces"),
 71	UCOUNT_ENTRY("max_pid_namespaces"),
 72	UCOUNT_ENTRY("max_uts_namespaces"),
 73	UCOUNT_ENTRY("max_ipc_namespaces"),
 74	UCOUNT_ENTRY("max_net_namespaces"),
 75	UCOUNT_ENTRY("max_mnt_namespaces"),
 76	UCOUNT_ENTRY("max_cgroup_namespaces"),
 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	setup_sysctl_set(&ns->set, &set_root, set_is_seen);
 86	tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL);
 87	if (tbl) {
 88		int i;
 89		for (i = 0; i < UCOUNT_COUNTS; i++) {
 90			tbl[i].data = &ns->ucount_max[i];
 91		}
 92		ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl);
 93	}
 94	if (!ns->sysctls) {
 95		kfree(tbl);
 96		retire_sysctl_set(&ns->set);
 97		return false;
 98	}
 99#endif
100	return true;
101}
102
103void retire_userns_sysctls(struct user_namespace *ns)
104{
105#ifdef CONFIG_SYSCTL
106	struct ctl_table *tbl;
107
108	tbl = ns->sysctls->ctl_table_arg;
109	unregister_sysctl_table(ns->sysctls);
110	retire_sysctl_set(&ns->set);
111	kfree(tbl);
112#endif
113}
114
115static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent)
116{
117	struct ucounts *ucounts;
118
119	hlist_for_each_entry(ucounts, hashent, node) {
120		if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns))
121			return ucounts;
122	}
123	return NULL;
124}
125
126static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
127{
128	struct hlist_head *hashent = ucounts_hashentry(ns, uid);
129	struct ucounts *ucounts, *new;
130
131	spin_lock_irq(&ucounts_lock);
132	ucounts = find_ucounts(ns, uid, hashent);
133	if (!ucounts) {
134		spin_unlock_irq(&ucounts_lock);
135
136		new = kzalloc(sizeof(*new), GFP_KERNEL);
137		if (!new)
138			return NULL;
139
140		new->ns = ns;
141		new->uid = uid;
142		new->count = 0;
143
144		spin_lock_irq(&ucounts_lock);
145		ucounts = find_ucounts(ns, uid, hashent);
146		if (ucounts) {
147			kfree(new);
148		} else {
149			hlist_add_head(&new->node, hashent);
150			ucounts = new;
151		}
152	}
153	if (ucounts->count == INT_MAX)
154		ucounts = NULL;
155	else
156		ucounts->count += 1;
157	spin_unlock_irq(&ucounts_lock);
158	return ucounts;
159}
160
161static void put_ucounts(struct ucounts *ucounts)
162{
163	unsigned long flags;
164
165	spin_lock_irqsave(&ucounts_lock, flags);
166	ucounts->count -= 1;
167	if (!ucounts->count)
168		hlist_del_init(&ucounts->node);
169	else
170		ucounts = NULL;
171	spin_unlock_irqrestore(&ucounts_lock, flags);
172
173	kfree(ucounts);
174}
175
176static inline bool atomic_inc_below(atomic_t *v, int u)
177{
178	int c, old;
179	c = atomic_read(v);
180	for (;;) {
181		if (unlikely(c >= u))
182			return false;
183		old = atomic_cmpxchg(v, c, c+1);
184		if (likely(old == c))
185			return true;
186		c = old;
187	}
188}
189
190struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
191			   enum ucount_type type)
192{
193	struct ucounts *ucounts, *iter, *bad;
194	struct user_namespace *tns;
195	ucounts = get_ucounts(ns, uid);
196	for (iter = ucounts; iter; iter = tns->ucounts) {
197		int max;
198		tns = iter->ns;
199		max = READ_ONCE(tns->ucount_max[type]);
200		if (!atomic_inc_below(&iter->ucount[type], max))
201			goto fail;
202	}
203	return ucounts;
204fail:
205	bad = iter;
206	for (iter = ucounts; iter != bad; iter = iter->ns->ucounts)
207		atomic_dec(&iter->ucount[type]);
208
209	put_ucounts(ucounts);
210	return NULL;
211}
212
213void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
214{
215	struct ucounts *iter;
216	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
217		int dec = atomic_dec_if_positive(&iter->ucount[type]);
218		WARN_ON_ONCE(dec < 0);
219	}
220	put_ucounts(ucounts);
221}
222
223static __init int user_namespace_sysctl_init(void)
224{
225#ifdef CONFIG_SYSCTL
226	static struct ctl_table_header *user_header;
227	static struct ctl_table empty[1];
228	/*
229	 * It is necessary to register the user directory in the
230	 * default set so that registrations in the child sets work
231	 * properly.
232	 */
233	user_header = register_sysctl("user", empty);
234	kmemleak_ignore(user_header);
235	BUG_ON(!user_header);
236	BUG_ON(!setup_userns_sysctls(&init_user_ns));
237#endif
238	return 0;
239}
240subsys_initcall(user_namespace_sysctl_init);