Root/ipc/namespace.c

1/*
2 * linux/ipc/namespace.c
3 * Copyright (C) 2006 Pavel Emelyanov <xemul@openvz.org> OpenVZ, SWsoft Inc.
4 */
5
6#include <linux/ipc.h>
7#include <linux/msg.h>
8#include <linux/ipc_namespace.h>
9#include <linux/rcupdate.h>
10#include <linux/nsproxy.h>
11#include <linux/slab.h>
12#include <linux/fs.h>
13#include <linux/mount.h>
14#include <linux/user_namespace.h>
15#include <linux/proc_fs.h>
16
17#include "util.h"
18
19static struct ipc_namespace *create_ipc_ns(struct task_struct *tsk,
20                       struct ipc_namespace *old_ns)
21{
22    struct ipc_namespace *ns;
23    int err;
24
25    ns = kmalloc(sizeof(struct ipc_namespace), GFP_KERNEL);
26    if (ns == NULL)
27        return ERR_PTR(-ENOMEM);
28
29    atomic_set(&ns->count, 1);
30    err = mq_init_ns(ns);
31    if (err) {
32        kfree(ns);
33        return ERR_PTR(err);
34    }
35    atomic_inc(&nr_ipc_ns);
36
37    sem_init_ns(ns);
38    msg_init_ns(ns);
39    shm_init_ns(ns);
40
41    /*
42     * msgmni has already been computed for the new ipc ns.
43     * Thus, do the ipcns creation notification before registering that
44     * new ipcns in the chain.
45     */
46    ipcns_notify(IPCNS_CREATED);
47    register_ipcns_notifier(ns);
48
49    ns->user_ns = get_user_ns(task_cred_xxx(tsk, user)->user_ns);
50
51    return ns;
52}
53
54struct ipc_namespace *copy_ipcs(unsigned long flags,
55                struct task_struct *tsk)
56{
57    struct ipc_namespace *ns = tsk->nsproxy->ipc_ns;
58
59    if (!(flags & CLONE_NEWIPC))
60        return get_ipc_ns(ns);
61    return create_ipc_ns(tsk, ns);
62}
63
64/*
65 * free_ipcs - free all ipcs of one type
66 * @ns: the namespace to remove the ipcs from
67 * @ids: the table of ipcs to free
68 * @free: the function called to free each individual ipc
69 *
70 * Called for each kind of ipc when an ipc_namespace exits.
71 */
72void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids,
73           void (*free)(struct ipc_namespace *, struct kern_ipc_perm *))
74{
75    struct kern_ipc_perm *perm;
76    int next_id;
77    int total, in_use;
78
79    down_write(&ids->rw_mutex);
80
81    in_use = ids->in_use;
82
83    for (total = 0, next_id = 0; total < in_use; next_id++) {
84        perm = idr_find(&ids->ipcs_idr, next_id);
85        if (perm == NULL)
86            continue;
87        ipc_lock_by_ptr(perm);
88        free(ns, perm);
89        total++;
90    }
91    up_write(&ids->rw_mutex);
92}
93
94static void free_ipc_ns(struct ipc_namespace *ns)
95{
96    /*
97     * Unregistering the hotplug notifier at the beginning guarantees
98     * that the ipc namespace won't be freed while we are inside the
99     * callback routine. Since the blocking_notifier_chain_XXX routines
100     * hold a rw lock on the notifier list, unregister_ipcns_notifier()
101     * won't take the rw lock before blocking_notifier_call_chain() has
102     * released the rd lock.
103     */
104    unregister_ipcns_notifier(ns);
105    sem_exit_ns(ns);
106    msg_exit_ns(ns);
107    shm_exit_ns(ns);
108    atomic_dec(&nr_ipc_ns);
109
110    /*
111     * Do the ipcns removal notification after decrementing nr_ipc_ns in
112     * order to have a correct value when recomputing msgmni.
113     */
114    ipcns_notify(IPCNS_REMOVED);
115    put_user_ns(ns->user_ns);
116    kfree(ns);
117}
118
119/*
120 * put_ipc_ns - drop a reference to an ipc namespace.
121 * @ns: the namespace to put
122 *
123 * If this is the last task in the namespace exiting, and
124 * it is dropping the refcount to 0, then it can race with
125 * a task in another ipc namespace but in a mounts namespace
126 * which has this ipcns's mqueuefs mounted, doing some action
127 * with one of the mqueuefs files. That can raise the refcount.
128 * So dropping the refcount, and raising the refcount when
129 * accessing it through the VFS, are protected with mq_lock.
130 *
131 * (Clearly, a task raising the refcount on its own ipc_ns
132 * needn't take mq_lock since it can't race with the last task
133 * in the ipcns exiting).
134 */
135void put_ipc_ns(struct ipc_namespace *ns)
136{
137    if (atomic_dec_and_lock(&ns->count, &mq_lock)) {
138        mq_clear_sbinfo(ns);
139        spin_unlock(&mq_lock);
140        mq_put_mnt(ns);
141        free_ipc_ns(ns);
142    }
143}
144
145static void *ipcns_get(struct task_struct *task)
146{
147    struct ipc_namespace *ns = NULL;
148    struct nsproxy *nsproxy;
149
150    rcu_read_lock();
151    nsproxy = task_nsproxy(task);
152    if (nsproxy)
153        ns = get_ipc_ns(nsproxy->ipc_ns);
154    rcu_read_unlock();
155
156    return ns;
157}
158
159static void ipcns_put(void *ns)
160{
161    return put_ipc_ns(ns);
162}
163
164static int ipcns_install(struct nsproxy *nsproxy, void *ns)
165{
166    /* Ditch state from the old ipc namespace */
167    exit_sem(current);
168    put_ipc_ns(nsproxy->ipc_ns);
169    nsproxy->ipc_ns = get_ipc_ns(ns);
170    return 0;
171}
172
173const struct proc_ns_operations ipcns_operations = {
174    .name = "ipc",
175    .type = CLONE_NEWIPC,
176    .get = ipcns_get,
177    .put = ipcns_put,
178    .install = ipcns_install,
179};
180

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