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/cred.h>
 12#include <linux/hash.h>
 13#include <linux/kmemleak.h>
 14#include <linux/user_namespace.h>
 15
 16#define UCOUNTS_HASHTABLE_BITS 10
 17static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)];
 18static DEFINE_SPINLOCK(ucounts_lock);
 19
 20#define ucounts_hashfn(ns, uid)						\
 21	hash_long((unsigned long)__kuid_val(uid) + (unsigned long)(ns), \
 22		  UCOUNTS_HASHTABLE_BITS)
 23#define ucounts_hashentry(ns, uid)	\
 24	(ucounts_hashtable + ucounts_hashfn(ns, uid))
 25
 26
 27#ifdef CONFIG_SYSCTL
 28static struct ctl_table_set *
 29set_lookup(struct ctl_table_root *root)
 30{
 31	return &current_user_ns()->set;
 32}
 33
 34static int set_is_seen(struct ctl_table_set *set)
 35{
 36	return &current_user_ns()->set == set;
 37}
 38
 39static int set_permissions(struct ctl_table_header *head,
 40				  struct ctl_table *table)
 41{
 42	struct user_namespace *user_ns =
 43		container_of(head->set, struct user_namespace, set);
 44	int mode;
 45
 46	/* Allow users with CAP_SYS_RESOURCE unrestrained access */
 47	if (ns_capable(user_ns, CAP_SYS_RESOURCE))
 48		mode = (table->mode & S_IRWXU) >> 6;
 49	else
 50	/* Allow all others at most read-only access */
 51		mode = table->mode & S_IROTH;
 52	return (mode << 6) | (mode << 3) | mode;
 53}
 54
 55static struct ctl_table_root set_root = {
 56	.lookup = set_lookup,
 57	.permissions = set_permissions,
 58};
 59
 60static int zero = 0;
 61static int int_max = INT_MAX;
 62#define UCOUNT_ENTRY(name)				\
 63	{						\
 64		.procname	= name,			\
 65		.maxlen		= sizeof(int),		\
 66		.mode		= 0644,			\
 67		.proc_handler	= proc_dointvec_minmax,	\
 68		.extra1		= &zero,		\
 69		.extra2		= &int_max,		\
 70	}
 71static struct ctl_table user_table[] = {
 72	UCOUNT_ENTRY("max_user_namespaces"),
 73	UCOUNT_ENTRY("max_pid_namespaces"),
 74	UCOUNT_ENTRY("max_uts_namespaces"),
 75	UCOUNT_ENTRY("max_ipc_namespaces"),
 76	UCOUNT_ENTRY("max_net_namespaces"),
 77	UCOUNT_ENTRY("max_mnt_namespaces"),
 78	UCOUNT_ENTRY("max_cgroup_namespaces"),
 79#ifdef CONFIG_INOTIFY_USER
 80	UCOUNT_ENTRY("max_inotify_instances"),
 81	UCOUNT_ENTRY("max_inotify_watches"),
 82#endif
 83	{ }
 84};
 85#endif /* CONFIG_SYSCTL */
 86
 87bool setup_userns_sysctls(struct user_namespace *ns)
 88{
 89#ifdef CONFIG_SYSCTL
 90	struct ctl_table *tbl;
 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);