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