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
16#include "util.h"
17
18static struct ipc_namespace *create_ipc_ns(struct task_struct *tsk,
19                       struct ipc_namespace *old_ns)
20{
21    struct ipc_namespace *ns;
22    int err;
23
24    ns = kmalloc(sizeof(struct ipc_namespace), GFP_KERNEL);
25    if (ns == NULL)
26        return ERR_PTR(-ENOMEM);
27
28    atomic_set(&ns->count, 1);
29    err = mq_init_ns(ns);
30    if (err) {
31        kfree(ns);
32        return ERR_PTR(err);
33    }
34    atomic_inc(&nr_ipc_ns);
35
36    sem_init_ns(ns);
37    msg_init_ns(ns);
38    shm_init_ns(ns);
39
40    /*
41     * msgmni has already been computed for the new ipc ns.
42     * Thus, do the ipcns creation notification before registering that
43     * new ipcns in the chain.
44     */
45    ipcns_notify(IPCNS_CREATED);
46    register_ipcns_notifier(ns);
47
48    ns->user_ns = get_user_ns(task_cred_xxx(tsk, user)->user_ns);
49
50    return ns;
51}
52
53struct ipc_namespace *copy_ipcs(unsigned long flags,
54                struct task_struct *tsk)
55{
56    struct ipc_namespace *ns = tsk->nsproxy->ipc_ns;
57
58    if (!(flags & CLONE_NEWIPC))
59        return get_ipc_ns(ns);
60    return create_ipc_ns(tsk, ns);
61}
62
63/*
64 * free_ipcs - free all ipcs of one type
65 * @ns: the namespace to remove the ipcs from
66 * @ids: the table of ipcs to free
67 * @free: the function called to free each individual ipc
68 *
69 * Called for each kind of ipc when an ipc_namespace exits.
70 */
71void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids,
72           void (*free)(struct ipc_namespace *, struct kern_ipc_perm *))
73{
74    struct kern_ipc_perm *perm;
75    int next_id;
76    int total, in_use;
77
78    down_write(&ids->rw_mutex);
79
80    in_use = ids->in_use;
81
82    for (total = 0, next_id = 0; total < in_use; next_id++) {
83        perm = idr_find(&ids->ipcs_idr, next_id);
84        if (perm == NULL)
85            continue;
86        ipc_lock_by_ptr(perm);
87        free(ns, perm);
88        total++;
89    }
90    up_write(&ids->rw_mutex);
91}
92
93static void free_ipc_ns(struct ipc_namespace *ns)
94{
95    /*
96     * Unregistering the hotplug notifier at the beginning guarantees
97     * that the ipc namespace won't be freed while we are inside the
98     * callback routine. Since the blocking_notifier_chain_XXX routines
99     * hold a rw lock on the notifier list, unregister_ipcns_notifier()
100     * won't take the rw lock before blocking_notifier_call_chain() has
101     * released the rd lock.
102     */
103    unregister_ipcns_notifier(ns);
104    sem_exit_ns(ns);
105    msg_exit_ns(ns);
106    shm_exit_ns(ns);
107    atomic_dec(&nr_ipc_ns);
108
109    /*
110     * Do the ipcns removal notification after decrementing nr_ipc_ns in
111     * order to have a correct value when recomputing msgmni.
112     */
113    ipcns_notify(IPCNS_REMOVED);
114    put_user_ns(ns->user_ns);
115    kfree(ns);
116}
117
118/*
119 * put_ipc_ns - drop a reference to an ipc namespace.
120 * @ns: the namespace to put
121 *
122 * If this is the last task in the namespace exiting, and
123 * it is dropping the refcount to 0, then it can race with
124 * a task in another ipc namespace but in a mounts namespace
125 * which has this ipcns's mqueuefs mounted, doing some action
126 * with one of the mqueuefs files. That can raise the refcount.
127 * So dropping the refcount, and raising the refcount when
128 * accessing it through the VFS, are protected with mq_lock.
129 *
130 * (Clearly, a task raising the refcount on its own ipc_ns
131 * needn't take mq_lock since it can't race with the last task
132 * in the ipcns exiting).
133 */
134void put_ipc_ns(struct ipc_namespace *ns)
135{
136    if (atomic_dec_and_lock(&ns->count, &mq_lock)) {
137        mq_clear_sbinfo(ns);
138        spin_unlock(&mq_lock);
139        mq_put_mnt(ns);
140        free_ipc_ns(ns);
141    }
142}
143

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