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![Giuseppe Scrivano](/assets/img/avatar_default.png)
the reason is to avoid a delay caused by the synchronize_rcu() call in kern_umount() when the mqueue mount is freed. the code: #define _GNU_SOURCE #include <sched.h> #include <error.h> #include <errno.h> #include <stdlib.h> int main() { int i; for (i = 0; i < 1000; i++) if (unshare(CLONE_NEWIPC) < 0) error(EXIT_FAILURE, errno, "unshare"); } goes from Command being timed: "./ipc-namespace" User time (seconds): 0.00 System time (seconds): 0.06 Percent of CPU this job got: 0% Elapsed (wall clock) time (h:mm:ss or m:ss): 0:08.05 to Command being timed: "./ipc-namespace" User time (seconds): 0.00 System time (seconds): 0.02 Percent of CPU this job got: 96% Elapsed (wall clock) time (h:mm:ss or m:ss): 0:00.03 Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Paul E. McKenney <paulmck@kernel.org> Reviewed-by: Waiman Long <longman@redhat.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Manfred Spraul <manfred@colorfullife.com> Link: http://lkml.kernel.org/r/20200225145419.527994-1-gscrivan@redhat.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
225 lines
5.1 KiB
C
225 lines
5.1 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* linux/ipc/namespace.c
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* Copyright (C) 2006 Pavel Emelyanov <xemul@openvz.org> OpenVZ, SWsoft Inc.
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*/
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#include <linux/ipc.h>
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#include <linux/msg.h>
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#include <linux/ipc_namespace.h>
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#include <linux/rcupdate.h>
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#include <linux/nsproxy.h>
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#include <linux/slab.h>
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#include <linux/cred.h>
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#include <linux/fs.h>
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#include <linux/mount.h>
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#include <linux/user_namespace.h>
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#include <linux/proc_ns.h>
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#include <linux/sched/task.h>
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#include "util.h"
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static struct ucounts *inc_ipc_namespaces(struct user_namespace *ns)
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{
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return inc_ucount(ns, current_euid(), UCOUNT_IPC_NAMESPACES);
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}
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static void dec_ipc_namespaces(struct ucounts *ucounts)
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{
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dec_ucount(ucounts, UCOUNT_IPC_NAMESPACES);
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}
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static struct ipc_namespace *create_ipc_ns(struct user_namespace *user_ns,
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struct ipc_namespace *old_ns)
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{
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struct ipc_namespace *ns;
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struct ucounts *ucounts;
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int err;
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err = -ENOSPC;
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ucounts = inc_ipc_namespaces(user_ns);
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if (!ucounts)
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goto fail;
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err = -ENOMEM;
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ns = kzalloc(sizeof(struct ipc_namespace), GFP_KERNEL);
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if (ns == NULL)
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goto fail_dec;
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err = ns_alloc_inum(&ns->ns);
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if (err)
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goto fail_free;
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ns->ns.ops = &ipcns_operations;
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refcount_set(&ns->count, 1);
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ns->user_ns = get_user_ns(user_ns);
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ns->ucounts = ucounts;
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err = mq_init_ns(ns);
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if (err)
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goto fail_put;
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sem_init_ns(ns);
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msg_init_ns(ns);
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shm_init_ns(ns);
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return ns;
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fail_put:
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put_user_ns(ns->user_ns);
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ns_free_inum(&ns->ns);
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fail_free:
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kfree(ns);
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fail_dec:
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dec_ipc_namespaces(ucounts);
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fail:
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return ERR_PTR(err);
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}
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struct ipc_namespace *copy_ipcs(unsigned long flags,
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struct user_namespace *user_ns, struct ipc_namespace *ns)
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{
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if (!(flags & CLONE_NEWIPC))
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return get_ipc_ns(ns);
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return create_ipc_ns(user_ns, ns);
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}
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/*
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* free_ipcs - free all ipcs of one type
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* @ns: the namespace to remove the ipcs from
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* @ids: the table of ipcs to free
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* @free: the function called to free each individual ipc
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*
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* Called for each kind of ipc when an ipc_namespace exits.
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*/
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void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids,
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void (*free)(struct ipc_namespace *, struct kern_ipc_perm *))
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{
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struct kern_ipc_perm *perm;
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int next_id;
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int total, in_use;
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down_write(&ids->rwsem);
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in_use = ids->in_use;
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for (total = 0, next_id = 0; total < in_use; next_id++) {
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perm = idr_find(&ids->ipcs_idr, next_id);
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if (perm == NULL)
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continue;
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rcu_read_lock();
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ipc_lock_object(perm);
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free(ns, perm);
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total++;
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}
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up_write(&ids->rwsem);
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}
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static void free_ipc_ns(struct ipc_namespace *ns)
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{
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/* mq_put_mnt() waits for a grace period as kern_unmount()
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* uses synchronize_rcu().
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*/
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mq_put_mnt(ns);
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sem_exit_ns(ns);
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msg_exit_ns(ns);
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shm_exit_ns(ns);
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dec_ipc_namespaces(ns->ucounts);
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put_user_ns(ns->user_ns);
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ns_free_inum(&ns->ns);
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kfree(ns);
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}
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static LLIST_HEAD(free_ipc_list);
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static void free_ipc(struct work_struct *unused)
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{
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struct llist_node *node = llist_del_all(&free_ipc_list);
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struct ipc_namespace *n, *t;
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llist_for_each_entry_safe(n, t, node, mnt_llist)
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free_ipc_ns(n);
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}
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/*
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* The work queue is used to avoid the cost of synchronize_rcu in kern_unmount.
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*/
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static DECLARE_WORK(free_ipc_work, free_ipc);
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/*
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* put_ipc_ns - drop a reference to an ipc namespace.
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* @ns: the namespace to put
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*
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* If this is the last task in the namespace exiting, and
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* it is dropping the refcount to 0, then it can race with
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* a task in another ipc namespace but in a mounts namespace
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* which has this ipcns's mqueuefs mounted, doing some action
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* with one of the mqueuefs files. That can raise the refcount.
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* So dropping the refcount, and raising the refcount when
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* accessing it through the VFS, are protected with mq_lock.
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*
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* (Clearly, a task raising the refcount on its own ipc_ns
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* needn't take mq_lock since it can't race with the last task
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* in the ipcns exiting).
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*/
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void put_ipc_ns(struct ipc_namespace *ns)
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{
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if (refcount_dec_and_lock(&ns->count, &mq_lock)) {
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mq_clear_sbinfo(ns);
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spin_unlock(&mq_lock);
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if (llist_add(&ns->mnt_llist, &free_ipc_list))
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schedule_work(&free_ipc_work);
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}
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}
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static inline struct ipc_namespace *to_ipc_ns(struct ns_common *ns)
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{
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return container_of(ns, struct ipc_namespace, ns);
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}
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static struct ns_common *ipcns_get(struct task_struct *task)
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{
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struct ipc_namespace *ns = NULL;
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struct nsproxy *nsproxy;
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task_lock(task);
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nsproxy = task->nsproxy;
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if (nsproxy)
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ns = get_ipc_ns(nsproxy->ipc_ns);
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task_unlock(task);
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return ns ? &ns->ns : NULL;
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}
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static void ipcns_put(struct ns_common *ns)
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{
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return put_ipc_ns(to_ipc_ns(ns));
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}
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static int ipcns_install(struct nsset *nsset, struct ns_common *new)
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{
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struct nsproxy *nsproxy = nsset->nsproxy;
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struct ipc_namespace *ns = to_ipc_ns(new);
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if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) ||
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!ns_capable(nsset->cred->user_ns, CAP_SYS_ADMIN))
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return -EPERM;
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put_ipc_ns(nsproxy->ipc_ns);
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nsproxy->ipc_ns = get_ipc_ns(ns);
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return 0;
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}
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static struct user_namespace *ipcns_owner(struct ns_common *ns)
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{
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return to_ipc_ns(ns)->user_ns;
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}
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const struct proc_ns_operations ipcns_operations = {
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.name = "ipc",
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.type = CLONE_NEWIPC,
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.get = ipcns_get,
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.put = ipcns_put,
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.install = ipcns_install,
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.owner = ipcns_owner,
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};
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