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 #include <linux/user_namespace.h>
  15
  16 #include "util.h"
  17
  18 static struct ipc_namespace *create_ipc_ns(struct task_struct *tsk,
  19                                            struct ipc_namespace *old_ns)
  20 {
  21         struct ipc_namespace *ns;
  22         int err;
  23
  24         ns = kmalloc(sizeof(struct ipc_namespace), GFP_KERNEL);
  25         if (ns == NULL)
  26                 return ERR_PTR(-ENOMEM);
  27
  28         atomic_set(&ns->count, 1);
  29         err = mq_init_ns(ns);
  30         if (err) {
  31                 kfree(ns);
  32                 return ERR_PTR(err);
  33         }
  34         atomic_inc(&nr_ipc_ns);
  35
  36         sem_init_ns(ns);
  37         msg_init_ns(ns);
  38         shm_init_ns(ns);
  39
  40         /*
  41          * msgmni has already been computed for the new ipc ns.
  42          * Thus, do the ipcns creation notification before registering that
  43          * new ipcns in the chain.
  44          */
  45         ipcns_notify(IPCNS_CREATED);
  46         register_ipcns_notifier(ns);
  47
  48         ns->user_ns = get_user_ns(task_cred_xxx(tsk, user)->user_ns);
  49
  50         return ns;
  51 }
  52
  53 struct ipc_namespace *copy_ipcs(unsigned long flags,
  54                                 struct task_struct *tsk)
  55 {
  56         struct ipc_namespace *ns = tsk->nsproxy->ipc_ns;
  57
  58         if (!(flags & CLONE_NEWIPC))
  59                 return get_ipc_ns(ns);
  60         return create_ipc_ns(tsk, ns);
  61 }
  62
  63 /*
  64  * free_ipcs - free all ipcs of one type
  65  * @ns:   the namespace to remove the ipcs from
  66  * @ids:  the table of ipcs to free
  67  * @free: the function called to free each individual ipc
  68  *
  69  * Called for each kind of ipc when an ipc_namespace exits.
  70  */
  71 void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids,
  72                void (*free)(struct ipc_namespace *, struct kern_ipc_perm *))
  73 {
  74         struct kern_ipc_perm *perm;
  75         int next_id;
  76         int total, in_use;
  77
  78         down_write(&ids->rw_mutex);
  79
  80         in_use = ids->in_use;
  81
  82         for (total = 0, next_id = 0; total < in_use; next_id++) {
  83                 perm = idr_find(&ids->ipcs_idr, next_id);
  84                 if (perm == NULL)
  85                         continue;
  86                 ipc_lock_by_ptr(perm);
  87                 free(ns, perm);
  88                 total++;
  89         }
  90         up_write(&ids->rw_mutex);
  91 }
  92
  93 static void free_ipc_ns(struct ipc_namespace *ns)
  94 {
  95         /*
  96          * Unregistering the hotplug notifier at the beginning guarantees
  97          * that the ipc namespace won't be freed while we are inside the
  98          * callback routine. Since the blocking_notifier_chain_XXX routines
  99          * hold a rw lock on the notifier list, unregister_ipcns_notifier()
 100          * won't take the rw lock before blocking_notifier_call_chain() has
 101          * released the rd lock.
 102          */
 103         unregister_ipcns_notifier(ns);
 104         sem_exit_ns(ns);
 105         msg_exit_ns(ns);
 106         shm_exit_ns(ns);
 107         atomic_dec(&nr_ipc_ns);
 108
 109         /*
 110          * Do the ipcns removal notification after decrementing nr_ipc_ns in
 111          * order to have a correct value when recomputing msgmni.
 112          */
 113         ipcns_notify(IPCNS_REMOVED);
 114         put_user_ns(ns->user_ns);
 115         kfree(ns);
 116 }
 117
 118 /*
 119  * put_ipc_ns - drop a reference to an ipc namespace.
 120  * @ns: the namespace to put
 121  *
 122  * If this is the last task in the namespace exiting, and
 123  * it is dropping the refcount to 0, then it can race with
 124  * a task in another ipc namespace but in a mounts namespace
 125  * which has this ipcns's mqueuefs mounted, doing some action
 126  * with one of the mqueuefs files.  That can raise the refcount.
 127  * So dropping the refcount, and raising the refcount when
 128  * accessing it through the VFS, are protected with mq_lock.
 129  *
 130  * (Clearly, a task raising the refcount on its own ipc_ns
 131  * needn't take mq_lock since it can't race with the last task
 132  * in the ipcns exiting).
 133  */
 134 void put_ipc_ns(struct ipc_namespace *ns)
 135 {
 136         if (atomic_dec_and_lock(&ns->count, &mq_lock)) {
 137                 mq_clear_sbinfo(ns);
 138                 spin_unlock(&mq_lock);
 139                 mq_put_mnt(ns);
 140                 free_ipc_ns(ns);
 141         }
 142 }