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