namespace.c

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/*
 * linux/ipc/namespace.c
 * Copyright (C) 2006 Pavel Emelyanov <xemul@openvz.org> OpenVZ, SWsoft Inc.
 */

#include <linux/ipc.h>
#include <linux/msg.h>
#include <linux/ipc_namespace.h>
#include <linux/rcupdate.h>
#include <linux/nsproxy.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/user_namespace.h>
#include <linux/proc_fs.h>

#include "util.h"

static struct ipc_namespace *create_ipc_ns(struct task_struct *tsk,
                       struct ipc_namespace *old_ns)
{
    struct ipc_namespace *ns;
    int err;

    ns = kmalloc(sizeof(struct ipc_namespace), GFP_KERNEL);
    if (ns == NULL)
        return ERR_PTR(-ENOMEM);

    atomic_set(&ns->count, 1);
    err = mq_init_ns(ns);
    if (err) {
        kfree(ns);
        return ERR_PTR(err);
    }
    atomic_inc(&nr_ipc_ns);

    sem_init_ns(ns);
    msg_init_ns(ns);
    shm_init_ns(ns);

    /*
     * msgmni has already been computed for the new ipc ns.
     * Thus, do the ipcns creation notification before registering that
     * new ipcns in the chain.
     */
    ipcns_notify(IPCNS_CREATED);
    register_ipcns_notifier(ns);

    ns->user_ns = get_user_ns(task_cred_xxx(tsk, user_ns));

    return ns;
}

struct ipc_namespace *copy_ipcs(unsigned long flags,
                struct task_struct *tsk)
{
    struct ipc_namespace *ns = tsk->nsproxy->ipc_ns;

    if (!(flags & CLONE_NEWIPC))
        return get_ipc_ns(ns);
    return create_ipc_ns(tsk, ns);
}

/*
 * free_ipcs - free all ipcs of one type
 * @ns:   the namespace to remove the ipcs from
 * @ids:  the table of ipcs to free
 * @free: the function called to free each individual ipc
 *
 * Called for each kind of ipc when an ipc_namespace exits.
 */
void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids,
           void (*free)(struct ipc_namespace *, struct kern_ipc_perm *))
{
    struct kern_ipc_perm *perm;
    int next_id;
    int total, in_use;

    down_write(&ids->rw_mutex);

    in_use = ids->in_use;

    for (total = 0, next_id = 0; total < in_use; next_id++) {
        perm = idr_find(&ids->ipcs_idr, next_id);
        if (perm == NULL)
            continue;
        ipc_lock_by_ptr(perm);
        free(ns, perm);
        total++;
    }
    up_write(&ids->rw_mutex);
}

static void free_ipc_ns(struct ipc_namespace *ns)
{
    /*
     * Unregistering the hotplug notifier at the beginning guarantees
     * that the ipc namespace won't be freed while we are inside the
     * callback routine. Since the blocking_notifier_chain_XXX routines
     * hold a rw lock on the notifier list, unregister_ipcns_notifier()
     * won't take the rw lock before blocking_notifier_call_chain() has
     * released the rd lock.
     */
    unregister_ipcns_notifier(ns);
    sem_exit_ns(ns);
    msg_exit_ns(ns);
    shm_exit_ns(ns);
    atomic_dec(&nr_ipc_ns);

    /*
     * Do the ipcns removal notification after decrementing nr_ipc_ns in
     * order to have a correct value when recomputing msgmni.
     */
    ipcns_notify(IPCNS_REMOVED);
    put_user_ns(ns->user_ns);
    kfree(ns);
}

/*
 * put_ipc_ns - drop a reference to an ipc namespace.
 * @ns: the namespace to put
 *
 * If this is the last task in the namespace exiting, and
 * it is dropping the refcount to 0, then it can race with
 * a task in another ipc namespace but in a mounts namespace
 * which has this ipcns's mqueuefs mounted, doing some action
 * with one of the mqueuefs files.  That can raise the refcount.
 * So dropping the refcount, and raising the refcount when
 * accessing it through the VFS, are protected with mq_lock.
 *
 * (Clearly, a task raising the refcount on its own ipc_ns
 * needn't take mq_lock since it can't race with the last task
 * in the ipcns exiting).
 */
void put_ipc_ns(struct ipc_namespace *ns)
{
    if (atomic_dec_and_lock(&ns->count, &mq_lock)) {
        mq_clear_sbinfo(ns);
        spin_unlock(&mq_lock);
        mq_put_mnt(ns);
        free_ipc_ns(ns);
    }
}

static void *ipcns_get(struct task_struct *task)
{
    struct ipc_namespace *ns = NULL;
    struct nsproxy *nsproxy;

    rcu_read_lock();
    nsproxy = task_nsproxy(task);
    if (nsproxy)
        ns = get_ipc_ns(nsproxy->ipc_ns);
    rcu_read_unlock();

    return ns;
}

static void ipcns_put(void *ns)
{
    return put_ipc_ns(ns);
}

static int ipcns_install(struct nsproxy *nsproxy, void *ns)
{
    /* Ditch state from the old ipc namespace */
    exit_sem(current);
    put_ipc_ns(nsproxy->ipc_ns);
    nsproxy->ipc_ns = get_ipc_ns(ns);
    return 0;
}

const struct proc_ns_operations ipcns_operations = {
    .name       = "ipc",
    .type       = CLONE_NEWIPC,
    .get        = ipcns_get,
    .put        = ipcns_put,
    .install    = ipcns_install,
};