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
  17 static struct ipc_namespace *clone_ipc_ns(struct ipc_namespace *old_ns)
  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
  49 struct ipc_namespace *copy_ipcs(unsigned long flags, struct ipc_namespace *ns)
  50 {
  51         struct ipc_namespace *new_ns;
  52
  53         BUG_ON(!ns);
  54         get_ipc_ns(ns);
  55
  56         if (!(flags & CLONE_NEWIPC))
  57                 return ns;
  58
  59         new_ns = clone_ipc_ns(ns);
  60
  61         put_ipc_ns(ns);
  62         return new_ns;
  63 }
  64
  65 /*
  66  * free_ipcs - free all ipcs of one type
  67  * @ns:   the namespace to remove the ipcs from
  68  * @ids:  the table of ipcs to free
  69  * @free: the function called to free each individual ipc
  70  *
  71  * Called for each kind of ipc when an ipc_namespace exits.
  72  */
  73 void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids,
  74                void (*free)(struct ipc_namespace *, struct kern_ipc_perm *))
  75 {
  76         struct kern_ipc_perm *perm;
  77         int next_id;
  78         int total, in_use;
  79
  80         down_write(&ids->rw_mutex);
  81
  82         in_use = ids->in_use;
  83
  84         for (total = 0, next_id = 0; total < in_use; next_id++) {
  85                 perm = idr_find(&ids->ipcs_idr, next_id);
  86                 if (perm == NULL)
  87                         continue;
  88                 ipc_lock_by_ptr(perm);
  89                 free(ns, perm);
  90                 total++;
  91         }
  92         up_write(&ids->rw_mutex);
  93 }
  94
  95 /*
  96  * put_ipc_ns - drop a reference to an ipc namespace.
  97  * @ns: the namespace to put
  98  *
  99  * If this is the last task in the namespace exiting, and
 100  * it is dropping the refcount to 0, then it can race with
 101  * a task in another ipc namespace but in a mounts namespace
 102  * which has this ipcns's mqueuefs mounted, doing some action
 103  * with one of the mqueuefs files.  That can raise the refcount.
 104  * So dropping the refcount, and raising the refcount when
 105  * accessing it through the VFS, are protected with mq_lock.
 106  *
 107  * (Clearly, a task raising the refcount on its own ipc_ns
 108  * needn't take mq_lock since it can't race with the last task
 109  * in the ipcns exiting).
 110  */
 111 void put_ipc_ns(struct ipc_namespace *ns)
 112 {
 113         if (atomic_dec_and_lock(&ns->count, &mq_lock)) {
 114                 mq_clear_sbinfo(ns);
 115                 spin_unlock(&mq_lock);
 116                 mq_put_mnt(ns);
 117                 free_ipc_ns(ns);
 118         }
 119 }
 120
 121 void free_ipc_ns(struct ipc_namespace *ns)
 122 {
 123         /*
 124          * Unregistering the hotplug notifier at the beginning guarantees
 125          * that the ipc namespace won't be freed while we are inside the
 126          * callback routine. Since the blocking_notifier_chain_XXX routines
 127          * hold a rw lock on the notifier list, unregister_ipcns_notifier()
 128          * won't take the rw lock before blocking_notifier_call_chain() has
 129          * released the rd lock.
 130          */
 131         unregister_ipcns_notifier(ns);
 132         sem_exit_ns(ns);
 133         msg_exit_ns(ns);
 134         shm_exit_ns(ns);
 135         kfree(ns);
 136         atomic_dec(&nr_ipc_ns);
 137
 138         /*
 139          * Do the ipcns removal notification after decrementing nr_ipc_ns in
 140          * order to have a correct value when recomputing msgmni.
 141          */
 142         ipcns_notify(IPCNS_REMOVED);
 143 }