xref: /linux/ipc/namespace.c (revision 18b19abc3709b109676ffd1f48dcd332c2e477d4)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * linux/ipc/namespace.c
4  * Copyright (C) 2006 Pavel Emelyanov <xemul@openvz.org> OpenVZ, SWsoft Inc.
5  */
6 
7 #include <linux/ipc.h>
8 #include <linux/msg.h>
9 #include <linux/ipc_namespace.h>
10 #include <linux/rcupdate.h>
11 #include <linux/nsproxy.h>
12 #include <linux/slab.h>
13 #include <linux/cred.h>
14 #include <linux/fs.h>
15 #include <linux/mount.h>
16 #include <linux/user_namespace.h>
17 #include <linux/proc_ns.h>
18 #include <linux/nstree.h>
19 #include <linux/sched/task.h>
20 
21 #include "util.h"
22 
23 /*
24  * The work queue is used to avoid the cost of synchronize_rcu in kern_unmount.
25  */
26 static void free_ipc(struct work_struct *unused);
27 static DECLARE_WORK(free_ipc_work, free_ipc);
28 
inc_ipc_namespaces(struct user_namespace * ns)29 static struct ucounts *inc_ipc_namespaces(struct user_namespace *ns)
30 {
31 	return inc_ucount(ns, current_euid(), UCOUNT_IPC_NAMESPACES);
32 }
33 
dec_ipc_namespaces(struct ucounts * ucounts)34 static void dec_ipc_namespaces(struct ucounts *ucounts)
35 {
36 	dec_ucount(ucounts, UCOUNT_IPC_NAMESPACES);
37 }
38 
create_ipc_ns(struct user_namespace * user_ns,struct ipc_namespace * old_ns)39 static struct ipc_namespace *create_ipc_ns(struct user_namespace *user_ns,
40 					   struct ipc_namespace *old_ns)
41 {
42 	struct ipc_namespace *ns;
43 	struct ucounts *ucounts;
44 	int err;
45 
46 	err = -ENOSPC;
47  again:
48 	ucounts = inc_ipc_namespaces(user_ns);
49 	if (!ucounts) {
50 		/*
51 		 * IPC namespaces are freed asynchronously, by free_ipc_work.
52 		 * If frees were pending, flush_work will wait, and
53 		 * return true. Fail the allocation if no frees are pending.
54 		 */
55 		if (flush_work(&free_ipc_work))
56 			goto again;
57 		goto fail;
58 	}
59 
60 	err = -ENOMEM;
61 	ns = kzalloc(sizeof(struct ipc_namespace), GFP_KERNEL_ACCOUNT);
62 	if (ns == NULL)
63 		goto fail_dec;
64 
65 	err = ns_common_init(ns);
66 	if (err)
67 		goto fail_free;
68 
69 	ns->user_ns = get_user_ns(user_ns);
70 	ns->ucounts = ucounts;
71 
72 	err = mq_init_ns(ns);
73 	if (err)
74 		goto fail_put;
75 
76 	err = -ENOMEM;
77 	if (!setup_mq_sysctls(ns))
78 		goto fail_put;
79 
80 	if (!setup_ipc_sysctls(ns))
81 		goto fail_mq;
82 
83 	err = msg_init_ns(ns);
84 	if (err)
85 		goto fail_ipc;
86 
87 	sem_init_ns(ns);
88 	shm_init_ns(ns);
89 	ns_tree_add(ns);
90 
91 	return ns;
92 
93 fail_ipc:
94 	retire_ipc_sysctls(ns);
95 fail_mq:
96 	retire_mq_sysctls(ns);
97 
98 fail_put:
99 	put_user_ns(ns->user_ns);
100 	ns_common_free(ns);
101 fail_free:
102 	kfree(ns);
103 fail_dec:
104 	dec_ipc_namespaces(ucounts);
105 fail:
106 	return ERR_PTR(err);
107 }
108 
copy_ipcs(u64 flags,struct user_namespace * user_ns,struct ipc_namespace * ns)109 struct ipc_namespace *copy_ipcs(u64 flags,
110 	struct user_namespace *user_ns, struct ipc_namespace *ns)
111 {
112 	if (!(flags & CLONE_NEWIPC))
113 		return get_ipc_ns(ns);
114 	return create_ipc_ns(user_ns, ns);
115 }
116 
117 /*
118  * free_ipcs - free all ipcs of one type
119  * @ns:   the namespace to remove the ipcs from
120  * @ids:  the table of ipcs to free
121  * @free: the function called to free each individual ipc
122  *
123  * Called for each kind of ipc when an ipc_namespace exits.
124  */
free_ipcs(struct ipc_namespace * ns,struct ipc_ids * ids,void (* free)(struct ipc_namespace *,struct kern_ipc_perm *))125 void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids,
126 	       void (*free)(struct ipc_namespace *, struct kern_ipc_perm *))
127 {
128 	struct kern_ipc_perm *perm;
129 	int next_id;
130 	int total, in_use;
131 
132 	down_write(&ids->rwsem);
133 
134 	in_use = ids->in_use;
135 
136 	for (total = 0, next_id = 0; total < in_use; next_id++) {
137 		perm = idr_find(&ids->ipcs_idr, next_id);
138 		if (perm == NULL)
139 			continue;
140 		rcu_read_lock();
141 		ipc_lock_object(perm);
142 		free(ns, perm);
143 		total++;
144 	}
145 	up_write(&ids->rwsem);
146 }
147 
free_ipc_ns(struct ipc_namespace * ns)148 static void free_ipc_ns(struct ipc_namespace *ns)
149 {
150 	/*
151 	 * Caller needs to wait for an RCU grace period to have passed
152 	 * after making the mount point inaccessible to new accesses.
153 	 */
154 	mntput(ns->mq_mnt);
155 	sem_exit_ns(ns);
156 	msg_exit_ns(ns);
157 	shm_exit_ns(ns);
158 
159 	retire_mq_sysctls(ns);
160 	retire_ipc_sysctls(ns);
161 
162 	dec_ipc_namespaces(ns->ucounts);
163 	put_user_ns(ns->user_ns);
164 	ns_common_free(ns);
165 	kfree(ns);
166 }
167 
168 static LLIST_HEAD(free_ipc_list);
free_ipc(struct work_struct * unused)169 static void free_ipc(struct work_struct *unused)
170 {
171 	struct llist_node *node = llist_del_all(&free_ipc_list);
172 	struct ipc_namespace *n, *t;
173 
174 	llist_for_each_entry_safe(n, t, node, mnt_llist)
175 		mnt_make_shortterm(n->mq_mnt);
176 
177 	/* Wait for any last users to have gone away. */
178 	synchronize_rcu();
179 
180 	llist_for_each_entry_safe(n, t, node, mnt_llist)
181 		free_ipc_ns(n);
182 }
183 
184 /*
185  * put_ipc_ns - drop a reference to an ipc namespace.
186  * @ns: the namespace to put
187  *
188  * If this is the last task in the namespace exiting, and
189  * it is dropping the refcount to 0, then it can race with
190  * a task in another ipc namespace but in a mounts namespace
191  * which has this ipcns's mqueuefs mounted, doing some action
192  * with one of the mqueuefs files.  That can raise the refcount.
193  * So dropping the refcount, and raising the refcount when
194  * accessing it through the VFS, are protected with mq_lock.
195  *
196  * (Clearly, a task raising the refcount on its own ipc_ns
197  * needn't take mq_lock since it can't race with the last task
198  * in the ipcns exiting).
199  */
put_ipc_ns(struct ipc_namespace * ns)200 void put_ipc_ns(struct ipc_namespace *ns)
201 {
202 	if (ns_ref_put_and_lock(ns, &mq_lock)) {
203 		mq_clear_sbinfo(ns);
204 		spin_unlock(&mq_lock);
205 
206 		ns_tree_remove(ns);
207 		if (llist_add(&ns->mnt_llist, &free_ipc_list))
208 			schedule_work(&free_ipc_work);
209 	}
210 }
211 
ipcns_get(struct task_struct * task)212 static struct ns_common *ipcns_get(struct task_struct *task)
213 {
214 	struct ipc_namespace *ns = NULL;
215 	struct nsproxy *nsproxy;
216 
217 	task_lock(task);
218 	nsproxy = task->nsproxy;
219 	if (nsproxy)
220 		ns = get_ipc_ns(nsproxy->ipc_ns);
221 	task_unlock(task);
222 
223 	return ns ? &ns->ns : NULL;
224 }
225 
ipcns_put(struct ns_common * ns)226 static void ipcns_put(struct ns_common *ns)
227 {
228 	return put_ipc_ns(to_ipc_ns(ns));
229 }
230 
ipcns_install(struct nsset * nsset,struct ns_common * new)231 static int ipcns_install(struct nsset *nsset, struct ns_common *new)
232 {
233 	struct nsproxy *nsproxy = nsset->nsproxy;
234 	struct ipc_namespace *ns = to_ipc_ns(new);
235 	if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) ||
236 	    !ns_capable(nsset->cred->user_ns, CAP_SYS_ADMIN))
237 		return -EPERM;
238 
239 	put_ipc_ns(nsproxy->ipc_ns);
240 	nsproxy->ipc_ns = get_ipc_ns(ns);
241 	return 0;
242 }
243 
ipcns_owner(struct ns_common * ns)244 static struct user_namespace *ipcns_owner(struct ns_common *ns)
245 {
246 	return to_ipc_ns(ns)->user_ns;
247 }
248 
249 const struct proc_ns_operations ipcns_operations = {
250 	.name		= "ipc",
251 	.get		= ipcns_get,
252 	.put		= ipcns_put,
253 	.install	= ipcns_install,
254 	.owner		= ipcns_owner,
255 };
256