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 *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
  49 struct 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  */
  64 void 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
  86 static 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  */
 126 void 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 }