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 *
set_lookup(struct ctl_table_root * root)30 set_lookup(struct ctl_table_root *root)
31 {
32 	return &current_user_ns()->set;
33 }
34 
set_is_seen(struct ctl_table_set * set)35 static int set_is_seen(struct ctl_table_set *set)
36 {
37 	return &current_user_ns()->set == set;
38 }
39 
set_permissions(struct ctl_table_header * head,struct ctl_table * table)40 static int set_permissions(struct ctl_table_header *head,
41 				  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 };
92 #endif /* CONFIG_SYSCTL */
93 
setup_userns_sysctls(struct user_namespace * ns)94 bool setup_userns_sysctls(struct user_namespace *ns)
95 {
96 #ifdef CONFIG_SYSCTL
97 	struct ctl_table *tbl;
98 
99 	BUILD_BUG_ON(ARRAY_SIZE(user_table) != UCOUNT_COUNTS + 1);
100 	setup_sysctl_set(&ns->set, &set_root, set_is_seen);
101 	tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL);
102 	if (tbl) {
103 		int i;
104 		for (i = 0; i < UCOUNT_COUNTS; i++) {
105 			tbl[i].data = &ns->ucount_max[i];
106 		}
107 		ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl,
108 						      ARRAY_SIZE(user_table));
109 	}
110 	if (!ns->sysctls) {
111 		kfree(tbl);
112 		retire_sysctl_set(&ns->set);
113 		return false;
114 	}
115 #endif
116 	return true;
117 }
118 
retire_userns_sysctls(struct user_namespace * ns)119 void retire_userns_sysctls(struct user_namespace *ns)
120 {
121 #ifdef CONFIG_SYSCTL
122 	struct ctl_table *tbl;
123 
124 	tbl = ns->sysctls->ctl_table_arg;
125 	unregister_sysctl_table(ns->sysctls);
126 	retire_sysctl_set(&ns->set);
127 	kfree(tbl);
128 #endif
129 }
130 
find_ucounts(struct user_namespace * ns,kuid_t uid,struct hlist_head * hashent)131 static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent)
132 {
133 	struct ucounts *ucounts;
134 
135 	hlist_for_each_entry(ucounts, hashent, node) {
136 		if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns))
137 			return ucounts;
138 	}
139 	return NULL;
140 }
141 
hlist_add_ucounts(struct ucounts * ucounts)142 static void hlist_add_ucounts(struct ucounts *ucounts)
143 {
144 	struct hlist_head *hashent = ucounts_hashentry(ucounts->ns, ucounts->uid);
145 	spin_lock_irq(&ucounts_lock);
146 	hlist_add_head(&ucounts->node, hashent);
147 	spin_unlock_irq(&ucounts_lock);
148 }
149 
get_ucounts_or_wrap(struct ucounts * ucounts)150 static inline bool get_ucounts_or_wrap(struct ucounts *ucounts)
151 {
152 	/* Returns true on a successful get, false if the count wraps. */
153 	return !atomic_add_negative(1, &ucounts->count);
154 }
155 
get_ucounts(struct ucounts * ucounts)156 struct ucounts *get_ucounts(struct ucounts *ucounts)
157 {
158 	if (!get_ucounts_or_wrap(ucounts)) {
159 		put_ucounts(ucounts);
160 		ucounts = NULL;
161 	}
162 	return ucounts;
163 }
164 
alloc_ucounts(struct user_namespace * ns,kuid_t uid)165 struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
166 {
167 	struct hlist_head *hashent = ucounts_hashentry(ns, uid);
168 	struct ucounts *ucounts, *new;
169 	bool wrapped;
170 
171 	spin_lock_irq(&ucounts_lock);
172 	ucounts = find_ucounts(ns, uid, hashent);
173 	if (!ucounts) {
174 		spin_unlock_irq(&ucounts_lock);
175 
176 		new = kzalloc(sizeof(*new), GFP_KERNEL);
177 		if (!new)
178 			return NULL;
179 
180 		new->ns = ns;
181 		new->uid = uid;
182 		atomic_set(&new->count, 1);
183 
184 		spin_lock_irq(&ucounts_lock);
185 		ucounts = find_ucounts(ns, uid, hashent);
186 		if (ucounts) {
187 			kfree(new);
188 		} else {
189 			hlist_add_head(&new->node, hashent);
190 			get_user_ns(new->ns);
191 			spin_unlock_irq(&ucounts_lock);
192 			return new;
193 		}
194 	}
195 	wrapped = !get_ucounts_or_wrap(ucounts);
196 	spin_unlock_irq(&ucounts_lock);
197 	if (wrapped) {
198 		put_ucounts(ucounts);
199 		return NULL;
200 	}
201 	return ucounts;
202 }
203 
put_ucounts(struct ucounts * ucounts)204 void put_ucounts(struct ucounts *ucounts)
205 {
206 	unsigned long flags;
207 
208 	if (atomic_dec_and_lock_irqsave(&ucounts->count, &ucounts_lock, flags)) {
209 		hlist_del_init(&ucounts->node);
210 		spin_unlock_irqrestore(&ucounts_lock, flags);
211 		put_user_ns(ucounts->ns);
212 		kfree(ucounts);
213 	}
214 }
215 
atomic_long_inc_below(atomic_long_t * v,int u)216 static inline bool atomic_long_inc_below(atomic_long_t *v, int u)
217 {
218 	long c, old;
219 	c = atomic_long_read(v);
220 	for (;;) {
221 		if (unlikely(c >= u))
222 			return false;
223 		old = atomic_long_cmpxchg(v, c, c+1);
224 		if (likely(old == c))
225 			return true;
226 		c = old;
227 	}
228 }
229 
inc_ucount(struct user_namespace * ns,kuid_t uid,enum ucount_type type)230 struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
231 			   enum ucount_type type)
232 {
233 	struct ucounts *ucounts, *iter, *bad;
234 	struct user_namespace *tns;
235 	ucounts = alloc_ucounts(ns, uid);
236 	for (iter = ucounts; iter; iter = tns->ucounts) {
237 		long max;
238 		tns = iter->ns;
239 		max = READ_ONCE(tns->ucount_max[type]);
240 		if (!atomic_long_inc_below(&iter->ucount[type], max))
241 			goto fail;
242 	}
243 	return ucounts;
244 fail:
245 	bad = iter;
246 	for (iter = ucounts; iter != bad; iter = iter->ns->ucounts)
247 		atomic_long_dec(&iter->ucount[type]);
248 
249 	put_ucounts(ucounts);
250 	return NULL;
251 }
252 
dec_ucount(struct ucounts * ucounts,enum ucount_type type)253 void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
254 {
255 	struct ucounts *iter;
256 	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
257 		long dec = atomic_long_dec_if_positive(&iter->ucount[type]);
258 		WARN_ON_ONCE(dec < 0);
259 	}
260 	put_ucounts(ucounts);
261 }
262 
inc_rlimit_ucounts(struct ucounts * ucounts,enum rlimit_type type,long v)263 long inc_rlimit_ucounts(struct ucounts *ucounts, enum rlimit_type type, long v)
264 {
265 	struct ucounts *iter;
266 	long max = LONG_MAX;
267 	long ret = 0;
268 
269 	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
270 		long new = atomic_long_add_return(v, &iter->rlimit[type]);
271 		if (new < 0 || new > max)
272 			ret = LONG_MAX;
273 		else if (iter == ucounts)
274 			ret = new;
275 		max = get_userns_rlimit_max(iter->ns, type);
276 	}
277 	return ret;
278 }
279 
dec_rlimit_ucounts(struct ucounts * ucounts,enum rlimit_type type,long v)280 bool dec_rlimit_ucounts(struct ucounts *ucounts, enum rlimit_type type, long v)
281 {
282 	struct ucounts *iter;
283 	long new = -1; /* Silence compiler warning */
284 	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
285 		long dec = atomic_long_sub_return(v, &iter->rlimit[type]);
286 		WARN_ON_ONCE(dec < 0);
287 		if (iter == ucounts)
288 			new = dec;
289 	}
290 	return (new == 0);
291 }
292 
do_dec_rlimit_put_ucounts(struct ucounts * ucounts,struct ucounts * last,enum rlimit_type type)293 static void do_dec_rlimit_put_ucounts(struct ucounts *ucounts,
294 				struct ucounts *last, enum rlimit_type type)
295 {
296 	struct ucounts *iter, *next;
297 	for (iter = ucounts; iter != last; iter = next) {
298 		long dec = atomic_long_sub_return(1, &iter->rlimit[type]);
299 		WARN_ON_ONCE(dec < 0);
300 		next = iter->ns->ucounts;
301 		if (dec == 0)
302 			put_ucounts(iter);
303 	}
304 }
305 
dec_rlimit_put_ucounts(struct ucounts * ucounts,enum rlimit_type type)306 void dec_rlimit_put_ucounts(struct ucounts *ucounts, enum rlimit_type type)
307 {
308 	do_dec_rlimit_put_ucounts(ucounts, NULL, type);
309 }
310 
inc_rlimit_get_ucounts(struct ucounts * ucounts,enum rlimit_type type)311 long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum rlimit_type type)
312 {
313 	/* Caller must hold a reference to ucounts */
314 	struct ucounts *iter;
315 	long max = LONG_MAX;
316 	long dec, ret = 0;
317 
318 	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
319 		long new = atomic_long_add_return(1, &iter->rlimit[type]);
320 		if (new < 0 || new > max)
321 			goto unwind;
322 		if (iter == ucounts)
323 			ret = new;
324 		max = get_userns_rlimit_max(iter->ns, type);
325 		/*
326 		 * Grab an extra ucount reference for the caller when
327 		 * the rlimit count was previously 0.
328 		 */
329 		if (new != 1)
330 			continue;
331 		if (!get_ucounts(iter))
332 			goto dec_unwind;
333 	}
334 	return ret;
335 dec_unwind:
336 	dec = atomic_long_sub_return(1, &iter->rlimit[type]);
337 	WARN_ON_ONCE(dec < 0);
338 unwind:
339 	do_dec_rlimit_put_ucounts(ucounts, iter, type);
340 	return 0;
341 }
342 
is_rlimit_overlimit(struct ucounts * ucounts,enum rlimit_type type,unsigned long rlimit)343 bool is_rlimit_overlimit(struct ucounts *ucounts, enum rlimit_type type, unsigned long rlimit)
344 {
345 	struct ucounts *iter;
346 	long max = rlimit;
347 	if (rlimit > LONG_MAX)
348 		max = LONG_MAX;
349 	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
350 		long val = get_rlimit_value(iter, type);
351 		if (val < 0 || val > max)
352 			return true;
353 		max = get_userns_rlimit_max(iter->ns, type);
354 	}
355 	return false;
356 }
357 
user_namespace_sysctl_init(void)358 static __init int user_namespace_sysctl_init(void)
359 {
360 #ifdef CONFIG_SYSCTL
361 	static struct ctl_table_header *user_header;
362 	static struct ctl_table empty[1];
363 	/*
364 	 * It is necessary to register the user directory in the
365 	 * default set so that registrations in the child sets work
366 	 * properly.
367 	 */
368 	user_header = register_sysctl_sz("user", empty, 0);
369 	kmemleak_ignore(user_header);
370 	BUG_ON(!user_header);
371 	BUG_ON(!setup_userns_sysctls(&init_user_ns));
372 #endif
373 	hlist_add_ucounts(&init_ucounts);
374 	inc_rlimit_ucounts(&init_ucounts, UCOUNT_RLIMIT_NPROC, 1);
375 	return 0;
376 }
377 subsys_initcall(user_namespace_sysctl_init);
378