linux/ipc/namespace.c
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   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_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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