xref: /openbmc/linux/kernel/pid_namespace.c (revision 9cfc5c90) 
1 /*
2  * Pid namespaces
3  *
4  * Authors:
5  *    (C) 2007 Pavel Emelyanov <xemul@openvz.org>, OpenVZ, SWsoft Inc.
6  *    (C) 2007 Sukadev Bhattiprolu <sukadev@us.ibm.com>, IBM
7  *     Many thanks to Oleg Nesterov for comments and help
8  *
9  */
10 
11 #include <linux/pid.h>
12 #include <linux/pid_namespace.h>
13 #include <linux/user_namespace.h>
14 #include <linux/syscalls.h>
15 #include <linux/err.h>
16 #include <linux/acct.h>
17 #include <linux/slab.h>
18 #include <linux/proc_ns.h>
19 #include <linux/reboot.h>
20 #include <linux/export.h>
21 
22 struct pid_cache {
23 	int nr_ids;
24 	char name[16];
25 	struct kmem_cache *cachep;
26 	struct list_head list;
27 };
28 
29 static LIST_HEAD(pid_caches_lh);
30 static DEFINE_MUTEX(pid_caches_mutex);
31 static struct kmem_cache *pid_ns_cachep;
32 
33 /*
34  * creates the kmem cache to allocate pids from.
35  * @nr_ids: the number of numerical ids this pid will have to carry
36  */
37 
38 static struct kmem_cache *create_pid_cachep(int nr_ids)
39 {
40 	struct pid_cache *pcache;
41 	struct kmem_cache *cachep;
42 
43 	mutex_lock(&pid_caches_mutex);
44 	list_for_each_entry(pcache, &pid_caches_lh, list)
45 		if (pcache->nr_ids == nr_ids)
46 			goto out;
47 
48 	pcache = kmalloc(sizeof(struct pid_cache), GFP_KERNEL);
49 	if (pcache == NULL)
50 		goto err_alloc;
51 
52 	snprintf(pcache->name, sizeof(pcache->name), "pid_%d", nr_ids);
53 	cachep = kmem_cache_create(pcache->name,
54 			sizeof(struct pid) + (nr_ids - 1) * sizeof(struct upid),
55 			0, SLAB_HWCACHE_ALIGN, NULL);
56 	if (cachep == NULL)
57 		goto err_cachep;
58 
59 	pcache->nr_ids = nr_ids;
60 	pcache->cachep = cachep;
61 	list_add(&pcache->list, &pid_caches_lh);
62 out:
63 	mutex_unlock(&pid_caches_mutex);
64 	return pcache->cachep;
65 
66 err_cachep:
67 	kfree(pcache);
68 err_alloc:
69 	mutex_unlock(&pid_caches_mutex);
70 	return NULL;
71 }
72 
73 static void proc_cleanup_work(struct work_struct *work)
74 {
75 	struct pid_namespace *ns = container_of(work, struct pid_namespace, proc_work);
76 	pid_ns_release_proc(ns);
77 }
78 
79 /* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
80 #define MAX_PID_NS_LEVEL 32
81 
82 static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns,
83 	struct pid_namespace *parent_pid_ns)
84 {
85 	struct pid_namespace *ns;
86 	unsigned int level = parent_pid_ns->level + 1;
87 	int i;
88 	int err;
89 
90 	if (level > MAX_PID_NS_LEVEL) {
91 		err = -EINVAL;
92 		goto out;
93 	}
94 
95 	err = -ENOMEM;
96 	ns = kmem_cache_zalloc(pid_ns_cachep, GFP_KERNEL);
97 	if (ns == NULL)
98 		goto out;
99 
100 	ns->pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
101 	if (!ns->pidmap[0].page)
102 		goto out_free;
103 
104 	ns->pid_cachep = create_pid_cachep(level + 1);
105 	if (ns->pid_cachep == NULL)
106 		goto out_free_map;
107 
108 	err = ns_alloc_inum(&ns->ns);
109 	if (err)
110 		goto out_free_map;
111 	ns->ns.ops = &pidns_operations;
112 
113 	kref_init(&ns->kref);
114 	ns->level = level;
115 	ns->parent = get_pid_ns(parent_pid_ns);
116 	ns->user_ns = get_user_ns(user_ns);
117 	ns->nr_hashed = PIDNS_HASH_ADDING;
118 	INIT_WORK(&ns->proc_work, proc_cleanup_work);
119 
120 	set_bit(0, ns->pidmap[0].page);
121 	atomic_set(&ns->pidmap[0].nr_free, BITS_PER_PAGE - 1);
122 
123 	for (i = 1; i < PIDMAP_ENTRIES; i++)
124 		atomic_set(&ns->pidmap[i].nr_free, BITS_PER_PAGE);
125 
126 	return ns;
127 
128 out_free_map:
129 	kfree(ns->pidmap[0].page);
130 out_free:
131 	kmem_cache_free(pid_ns_cachep, ns);
132 out:
133 	return ERR_PTR(err);
134 }
135 
136 static void delayed_free_pidns(struct rcu_head *p)
137 {
138 	kmem_cache_free(pid_ns_cachep,
139 			container_of(p, struct pid_namespace, rcu));
140 }
141 
142 static void destroy_pid_namespace(struct pid_namespace *ns)
143 {
144 	int i;
145 
146 	ns_free_inum(&ns->ns);
147 	for (i = 0; i < PIDMAP_ENTRIES; i++)
148 		kfree(ns->pidmap[i].page);
149 	put_user_ns(ns->user_ns);
150 	call_rcu(&ns->rcu, delayed_free_pidns);
151 }
152 
153 struct pid_namespace *copy_pid_ns(unsigned long flags,
154 	struct user_namespace *user_ns, struct pid_namespace *old_ns)
155 {
156 	if (!(flags & CLONE_NEWPID))
157 		return get_pid_ns(old_ns);
158 	if (task_active_pid_ns(current) != old_ns)
159 		return ERR_PTR(-EINVAL);
160 	return create_pid_namespace(user_ns, old_ns);
161 }
162 
163 static void free_pid_ns(struct kref *kref)
164 {
165 	struct pid_namespace *ns;
166 
167 	ns = container_of(kref, struct pid_namespace, kref);
168 	destroy_pid_namespace(ns);
169 }
170 
171 void put_pid_ns(struct pid_namespace *ns)
172 {
173 	struct pid_namespace *parent;
174 
175 	while (ns != &init_pid_ns) {
176 		parent = ns->parent;
177 		if (!kref_put(&ns->kref, free_pid_ns))
178 			break;
179 		ns = parent;
180 	}
181 }
182 EXPORT_SYMBOL_GPL(put_pid_ns);
183 
184 void zap_pid_ns_processes(struct pid_namespace *pid_ns)
185 {
186 	int nr;
187 	int rc;
188 	struct task_struct *task, *me = current;
189 	int init_pids = thread_group_leader(me) ? 1 : 2;
190 
191 	/* Don't allow any more processes into the pid namespace */
192 	disable_pid_allocation(pid_ns);
193 
194 	/*
195 	 * Ignore SIGCHLD causing any terminated children to autoreap.
196 	 * This speeds up the namespace shutdown, plus see the comment
197 	 * below.
198 	 */
199 	spin_lock_irq(&me->sighand->siglock);
200 	me->sighand->action[SIGCHLD - 1].sa.sa_handler = SIG_IGN;
201 	spin_unlock_irq(&me->sighand->siglock);
202 
203 	/*
204 	 * The last thread in the cgroup-init thread group is terminating.
205 	 * Find remaining pid_ts in the namespace, signal and wait for them
206 	 * to exit.
207 	 *
208 	 * Note:  This signals each threads in the namespace - even those that
209 	 * 	  belong to the same thread group, To avoid this, we would have
210 	 * 	  to walk the entire tasklist looking a processes in this
211 	 * 	  namespace, but that could be unnecessarily expensive if the
212 	 * 	  pid namespace has just a few processes. Or we need to
213 	 * 	  maintain a tasklist for each pid namespace.
214 	 *
215 	 */
216 	read_lock(&tasklist_lock);
217 	nr = next_pidmap(pid_ns, 1);
218 	while (nr > 0) {
219 		rcu_read_lock();
220 
221 		task = pid_task(find_vpid(nr), PIDTYPE_PID);
222 		if (task && !__fatal_signal_pending(task))
223 			send_sig_info(SIGKILL, SEND_SIG_FORCED, task);
224 
225 		rcu_read_unlock();
226 
227 		nr = next_pidmap(pid_ns, nr);
228 	}
229 	read_unlock(&tasklist_lock);
230 
231 	/*
232 	 * Reap the EXIT_ZOMBIE children we had before we ignored SIGCHLD.
233 	 * sys_wait4() will also block until our children traced from the
234 	 * parent namespace are detached and become EXIT_DEAD.
235 	 */
236 	do {
237 		clear_thread_flag(TIF_SIGPENDING);
238 		rc = sys_wait4(-1, NULL, __WALL, NULL);
239 	} while (rc != -ECHILD);
240 
241 	/*
242 	 * sys_wait4() above can't reap the EXIT_DEAD children but we do not
243 	 * really care, we could reparent them to the global init. We could
244 	 * exit and reap ->child_reaper even if it is not the last thread in
245 	 * this pid_ns, free_pid(nr_hashed == 0) calls proc_cleanup_work(),
246 	 * pid_ns can not go away until proc_kill_sb() drops the reference.
247 	 *
248 	 * But this ns can also have other tasks injected by setns()+fork().
249 	 * Again, ignoring the user visible semantics we do not really need
250 	 * to wait until they are all reaped, but they can be reparented to
251 	 * us and thus we need to ensure that pid->child_reaper stays valid
252 	 * until they all go away. See free_pid()->wake_up_process().
253 	 *
254 	 * We rely on ignored SIGCHLD, an injected zombie must be autoreaped
255 	 * if reparented.
256 	 */
257 	for (;;) {
258 		set_current_state(TASK_UNINTERRUPTIBLE);
259 		if (pid_ns->nr_hashed == init_pids)
260 			break;
261 		schedule();
262 	}
263 	__set_current_state(TASK_RUNNING);
264 
265 	if (pid_ns->reboot)
266 		current->signal->group_exit_code = pid_ns->reboot;
267 
268 	acct_exit_ns(pid_ns);
269 	return;
270 }
271 
272 #ifdef CONFIG_CHECKPOINT_RESTORE
273 static int pid_ns_ctl_handler(struct ctl_table *table, int write,
274 		void __user *buffer, size_t *lenp, loff_t *ppos)
275 {
276 	struct pid_namespace *pid_ns = task_active_pid_ns(current);
277 	struct ctl_table tmp = *table;
278 
279 	if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN))
280 		return -EPERM;
281 
282 	/*
283 	 * Writing directly to ns' last_pid field is OK, since this field
284 	 * is volatile in a living namespace anyway and a code writing to
285 	 * it should synchronize its usage with external means.
286 	 */
287 
288 	tmp.data = &pid_ns->last_pid;
289 	return proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
290 }
291 
292 extern int pid_max;
293 static int zero = 0;
294 static struct ctl_table pid_ns_ctl_table[] = {
295 	{
296 		.procname = "ns_last_pid",
297 		.maxlen = sizeof(int),
298 		.mode = 0666, /* permissions are checked in the handler */
299 		.proc_handler = pid_ns_ctl_handler,
300 		.extra1 = &zero,
301 		.extra2 = &pid_max,
302 	},
303 	{ }
304 };
305 static struct ctl_path kern_path[] = { { .procname = "kernel", }, { } };
306 #endif	/* CONFIG_CHECKPOINT_RESTORE */
307 
308 int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd)
309 {
310 	if (pid_ns == &init_pid_ns)
311 		return 0;
312 
313 	switch (cmd) {
314 	case LINUX_REBOOT_CMD_RESTART2:
315 	case LINUX_REBOOT_CMD_RESTART:
316 		pid_ns->reboot = SIGHUP;
317 		break;
318 
319 	case LINUX_REBOOT_CMD_POWER_OFF:
320 	case LINUX_REBOOT_CMD_HALT:
321 		pid_ns->reboot = SIGINT;
322 		break;
323 	default:
324 		return -EINVAL;
325 	}
326 
327 	read_lock(&tasklist_lock);
328 	force_sig(SIGKILL, pid_ns->child_reaper);
329 	read_unlock(&tasklist_lock);
330 
331 	do_exit(0);
332 
333 	/* Not reached */
334 	return 0;
335 }
336 
337 static inline struct pid_namespace *to_pid_ns(struct ns_common *ns)
338 {
339 	return container_of(ns, struct pid_namespace, ns);
340 }
341 
342 static struct ns_common *pidns_get(struct task_struct *task)
343 {
344 	struct pid_namespace *ns;
345 
346 	rcu_read_lock();
347 	ns = task_active_pid_ns(task);
348 	if (ns)
349 		get_pid_ns(ns);
350 	rcu_read_unlock();
351 
352 	return ns ? &ns->ns : NULL;
353 }
354 
355 static void pidns_put(struct ns_common *ns)
356 {
357 	put_pid_ns(to_pid_ns(ns));
358 }
359 
360 static int pidns_install(struct nsproxy *nsproxy, struct ns_common *ns)
361 {
362 	struct pid_namespace *active = task_active_pid_ns(current);
363 	struct pid_namespace *ancestor, *new = to_pid_ns(ns);
364 
365 	if (!ns_capable(new->user_ns, CAP_SYS_ADMIN) ||
366 	    !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
367 		return -EPERM;
368 
369 	/*
370 	 * Only allow entering the current active pid namespace
371 	 * or a child of the current active pid namespace.
372 	 *
373 	 * This is required for fork to return a usable pid value and
374 	 * this maintains the property that processes and their
375 	 * children can not escape their current pid namespace.
376 	 */
377 	if (new->level < active->level)
378 		return -EINVAL;
379 
380 	ancestor = new;
381 	while (ancestor->level > active->level)
382 		ancestor = ancestor->parent;
383 	if (ancestor != active)
384 		return -EINVAL;
385 
386 	put_pid_ns(nsproxy->pid_ns_for_children);
387 	nsproxy->pid_ns_for_children = get_pid_ns(new);
388 	return 0;
389 }
390 
391 const struct proc_ns_operations pidns_operations = {
392 	.name		= "pid",
393 	.type		= CLONE_NEWPID,
394 	.get		= pidns_get,
395 	.put		= pidns_put,
396 	.install	= pidns_install,
397 };
398 
399 static __init int pid_namespaces_init(void)
400 {
401 	pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC);
402 
403 #ifdef CONFIG_CHECKPOINT_RESTORE
404 	register_sysctl_paths(kern_path, pid_ns_ctl_table);
405 #endif
406 	return 0;
407 }
408 
409 __initcall(pid_namespaces_init);
410