util.c revision f8b59184
1/*
2 * linux/ipc/util.c
3 * Copyright (C) 1992 Krishna Balasubramanian
4 *
5 * Sep 1997 - Call suser() last after "normal" permission checks so we
6 *            get BSD style process accounting right.
7 *            Occurs in several places in the IPC code.
8 *            Chris Evans, <chris@ferret.lmh.ox.ac.uk>
9 * Nov 1999 - ipc helper functions, unified SMP locking
10 *	      Manfred Spraul <manfred@colorfullife.com>
11 * Oct 2002 - One lock per IPC id. RCU ipc_free for lock-free grow_ary().
12 *            Mingming Cao <cmm@us.ibm.com>
13 * Mar 2006 - support for audit of ipc object properties
14 *            Dustin Kirkland <dustin.kirkland@us.ibm.com>
15 * Jun 2006 - namespaces ssupport
16 *            OpenVZ, SWsoft Inc.
17 *            Pavel Emelianov <xemul@openvz.org>
18 *
19 * General sysv ipc locking scheme:
20 *	rcu_read_lock()
21 *          obtain the ipc object (kern_ipc_perm) by looking up the id in an idr
22 *	    tree.
23 *	    - perform initial checks (capabilities, auditing and permission,
24 *	      etc).
25 *	    - perform read-only operations, such as STAT, INFO commands.
26 *	      acquire the ipc lock (kern_ipc_perm.lock) through
27 *	      ipc_lock_object()
28 *		- perform data updates, such as SET, RMID commands and
29 *		  mechanism-specific operations (semop/semtimedop,
30 *		  msgsnd/msgrcv, shmat/shmdt).
31 *	    drop the ipc lock, through ipc_unlock_object().
32 *	rcu_read_unlock()
33 *
34 *  The ids->rwsem must be taken when:
35 *	- creating, removing and iterating the existing entries in ipc
36 *	  identifier sets.
37 *	- iterating through files under /proc/sysvipc/
38 *
39 *  Note that sems have a special fast path that avoids kern_ipc_perm.lock -
40 *  see sem_lock().
41 */
42
43#include <linux/mm.h>
44#include <linux/shm.h>
45#include <linux/init.h>
46#include <linux/msg.h>
47#include <linux/vmalloc.h>
48#include <linux/slab.h>
49#include <linux/notifier.h>
50#include <linux/capability.h>
51#include <linux/highuid.h>
52#include <linux/security.h>
53#include <linux/rcupdate.h>
54#include <linux/workqueue.h>
55#include <linux/seq_file.h>
56#include <linux/proc_fs.h>
57#include <linux/audit.h>
58#include <linux/nsproxy.h>
59#include <linux/rwsem.h>
60#include <linux/memory.h>
61#include <linux/ipc_namespace.h>
62
63#include <asm/unistd.h>
64
65#include "util.h"
66
67struct ipc_proc_iface {
68	const char *path;
69	const char *header;
70	int ids;
71	int (*show)(struct seq_file *, void *);
72};
73
74/**
75 * ipc_init - initialise ipc subsystem
76 *
77 * The various sysv ipc resources (semaphores, messages and shared
78 * memory) are initialised.
79 *
80 * A callback routine is registered into the memory hotplug notifier
81 * chain: since msgmni scales to lowmem this callback routine will be
82 * called upon successful memory add / remove to recompute msmgni.
83 */
84static int __init ipc_init(void)
85{
86	sem_init();
87	msg_init();
88	shm_init();
89	return 0;
90}
91device_initcall(ipc_init);
92
93/**
94 * ipc_init_ids	- initialise ipc identifiers
95 * @ids: ipc identifier set
96 *
97 * Set up the sequence range to use for the ipc identifier range (limited
98 * below IPCMNI) then initialise the ids idr.
99 */
100void ipc_init_ids(struct ipc_ids *ids)
101{
102	ids->in_use = 0;
103	ids->seq = 0;
104	ids->next_id = -1;
105	init_rwsem(&ids->rwsem);
106	idr_init(&ids->ipcs_idr);
107}
108
109#ifdef CONFIG_PROC_FS
110static const struct file_operations sysvipc_proc_fops;
111/**
112 * ipc_init_proc_interface -  create a proc interface for sysipc types using a seq_file interface.
113 * @path: Path in procfs
114 * @header: Banner to be printed at the beginning of the file.
115 * @ids: ipc id table to iterate.
116 * @show: show routine.
117 */
118void __init ipc_init_proc_interface(const char *path, const char *header,
119		int ids, int (*show)(struct seq_file *, void *))
120{
121	struct proc_dir_entry *pde;
122	struct ipc_proc_iface *iface;
123
124	iface = kmalloc(sizeof(*iface), GFP_KERNEL);
125	if (!iface)
126		return;
127	iface->path	= path;
128	iface->header	= header;
129	iface->ids	= ids;
130	iface->show	= show;
131
132	pde = proc_create_data(path,
133			       S_IRUGO,        /* world readable */
134			       NULL,           /* parent dir */
135			       &sysvipc_proc_fops,
136			       iface);
137	if (!pde)
138		kfree(iface);
139}
140#endif
141
142/**
143 * ipc_findkey	- find a key in an ipc identifier set
144 * @ids: ipc identifier set
145 * @key: key to find
146 *
147 * Returns the locked pointer to the ipc structure if found or NULL
148 * otherwise. If key is found ipc points to the owning ipc structure
149 *
150 * Called with ipc_ids.rwsem held.
151 */
152static struct kern_ipc_perm *ipc_findkey(struct ipc_ids *ids, key_t key)
153{
154	struct kern_ipc_perm *ipc;
155	int next_id;
156	int total;
157
158	for (total = 0, next_id = 0; total < ids->in_use; next_id++) {
159		ipc = idr_find(&ids->ipcs_idr, next_id);
160
161		if (ipc == NULL)
162			continue;
163
164		if (ipc->key != key) {
165			total++;
166			continue;
167		}
168
169		rcu_read_lock();
170		ipc_lock_object(ipc);
171		return ipc;
172	}
173
174	return NULL;
175}
176
177/**
178 * ipc_get_maxid - get the last assigned id
179 * @ids: ipc identifier set
180 *
181 * Called with ipc_ids.rwsem held.
182 */
183int ipc_get_maxid(struct ipc_ids *ids)
184{
185	struct kern_ipc_perm *ipc;
186	int max_id = -1;
187	int total, id;
188
189	if (ids->in_use == 0)
190		return -1;
191
192	if (ids->in_use == IPCMNI)
193		return IPCMNI - 1;
194
195	/* Look for the last assigned id */
196	total = 0;
197	for (id = 0; id < IPCMNI && total < ids->in_use; id++) {
198		ipc = idr_find(&ids->ipcs_idr, id);
199		if (ipc != NULL) {
200			max_id = id;
201			total++;
202		}
203	}
204	return max_id;
205}
206
207/**
208 * ipc_addid - add an ipc identifier
209 * @ids: ipc identifier set
210 * @new: new ipc permission set
211 * @size: limit for the number of used ids
212 *
213 * Add an entry 'new' to the ipc ids idr. The permissions object is
214 * initialised and the first free entry is set up and the id assigned
215 * is returned. The 'new' entry is returned in a locked state on success.
216 * On failure the entry is not locked and a negative err-code is returned.
217 *
218 * Called with writer ipc_ids.rwsem held.
219 */
220int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int size)
221{
222	kuid_t euid;
223	kgid_t egid;
224	int id;
225	int next_id = ids->next_id;
226
227	if (size > IPCMNI)
228		size = IPCMNI;
229
230	if (ids->in_use >= size)
231		return -ENOSPC;
232
233	idr_preload(GFP_KERNEL);
234
235	spin_lock_init(&new->lock);
236	new->deleted = false;
237	rcu_read_lock();
238	spin_lock(&new->lock);
239
240	id = idr_alloc(&ids->ipcs_idr, new,
241		       (next_id < 0) ? 0 : ipcid_to_idx(next_id), 0,
242		       GFP_NOWAIT);
243	idr_preload_end();
244	if (id < 0) {
245		spin_unlock(&new->lock);
246		rcu_read_unlock();
247		return id;
248	}
249
250	ids->in_use++;
251
252	current_euid_egid(&euid, &egid);
253	new->cuid = new->uid = euid;
254	new->gid = new->cgid = egid;
255
256	if (next_id < 0) {
257		new->seq = ids->seq++;
258		if (ids->seq > IPCID_SEQ_MAX)
259			ids->seq = 0;
260	} else {
261		new->seq = ipcid_to_seqx(next_id);
262		ids->next_id = -1;
263	}
264
265	new->id = ipc_buildid(id, new->seq);
266	return id;
267}
268
269/**
270 * ipcget_new -	create a new ipc object
271 * @ns: ipc namespace
272 * @ids: ipc identifier set
273 * @ops: the actual creation routine to call
274 * @params: its parameters
275 *
276 * This routine is called by sys_msgget, sys_semget() and sys_shmget()
277 * when the key is IPC_PRIVATE.
278 */
279static int ipcget_new(struct ipc_namespace *ns, struct ipc_ids *ids,
280		const struct ipc_ops *ops, struct ipc_params *params)
281{
282	int err;
283
284	down_write(&ids->rwsem);
285	err = ops->getnew(ns, params);
286	up_write(&ids->rwsem);
287	return err;
288}
289
290/**
291 * ipc_check_perms - check security and permissions for an ipc object
292 * @ns: ipc namespace
293 * @ipcp: ipc permission set
294 * @ops: the actual security routine to call
295 * @params: its parameters
296 *
297 * This routine is called by sys_msgget(), sys_semget() and sys_shmget()
298 * when the key is not IPC_PRIVATE and that key already exists in the
299 * ds IDR.
300 *
301 * On success, the ipc id is returned.
302 *
303 * It is called with ipc_ids.rwsem and ipcp->lock held.
304 */
305static int ipc_check_perms(struct ipc_namespace *ns,
306			   struct kern_ipc_perm *ipcp,
307			   const struct ipc_ops *ops,
308			   struct ipc_params *params)
309{
310	int err;
311
312	if (ipcperms(ns, ipcp, params->flg))
313		err = -EACCES;
314	else {
315		err = ops->associate(ipcp, params->flg);
316		if (!err)
317			err = ipcp->id;
318	}
319
320	return err;
321}
322
323/**
324 * ipcget_public - get an ipc object or create a new one
325 * @ns: ipc namespace
326 * @ids: ipc identifier set
327 * @ops: the actual creation routine to call
328 * @params: its parameters
329 *
330 * This routine is called by sys_msgget, sys_semget() and sys_shmget()
331 * when the key is not IPC_PRIVATE.
332 * It adds a new entry if the key is not found and does some permission
333 * / security checkings if the key is found.
334 *
335 * On success, the ipc id is returned.
336 */
337static int ipcget_public(struct ipc_namespace *ns, struct ipc_ids *ids,
338		const struct ipc_ops *ops, struct ipc_params *params)
339{
340	struct kern_ipc_perm *ipcp;
341	int flg = params->flg;
342	int err;
343
344	/*
345	 * Take the lock as a writer since we are potentially going to add
346	 * a new entry + read locks are not "upgradable"
347	 */
348	down_write(&ids->rwsem);
349	ipcp = ipc_findkey(ids, params->key);
350	if (ipcp == NULL) {
351		/* key not used */
352		if (!(flg & IPC_CREAT))
353			err = -ENOENT;
354		else
355			err = ops->getnew(ns, params);
356	} else {
357		/* ipc object has been locked by ipc_findkey() */
358
359		if (flg & IPC_CREAT && flg & IPC_EXCL)
360			err = -EEXIST;
361		else {
362			err = 0;
363			if (ops->more_checks)
364				err = ops->more_checks(ipcp, params);
365			if (!err)
366				/*
367				 * ipc_check_perms returns the IPC id on
368				 * success
369				 */
370				err = ipc_check_perms(ns, ipcp, ops, params);
371		}
372		ipc_unlock(ipcp);
373	}
374	up_write(&ids->rwsem);
375
376	return err;
377}
378
379
380/**
381 * ipc_rmid - remove an ipc identifier
382 * @ids: ipc identifier set
383 * @ipcp: ipc perm structure containing the identifier to remove
384 *
385 * ipc_ids.rwsem (as a writer) and the spinlock for this ID are held
386 * before this function is called, and remain locked on the exit.
387 */
388void ipc_rmid(struct ipc_ids *ids, struct kern_ipc_perm *ipcp)
389{
390	int lid = ipcid_to_idx(ipcp->id);
391
392	idr_remove(&ids->ipcs_idr, lid);
393	ids->in_use--;
394	ipcp->deleted = true;
395}
396
397/**
398 * ipc_alloc -	allocate ipc space
399 * @size: size desired
400 *
401 * Allocate memory from the appropriate pools and return a pointer to it.
402 * NULL is returned if the allocation fails
403 */
404void *ipc_alloc(int size)
405{
406	void *out;
407	if (size > PAGE_SIZE)
408		out = vmalloc(size);
409	else
410		out = kmalloc(size, GFP_KERNEL);
411	return out;
412}
413
414/**
415 * ipc_free - free ipc space
416 * @ptr: pointer returned by ipc_alloc
417 * @size: size of block
418 *
419 * Free a block created with ipc_alloc(). The caller must know the size
420 * used in the allocation call.
421 */
422void ipc_free(void *ptr, int size)
423{
424	if (size > PAGE_SIZE)
425		vfree(ptr);
426	else
427		kfree(ptr);
428}
429
430/**
431 * ipc_rcu_alloc - allocate ipc and rcu space
432 * @size: size desired
433 *
434 * Allocate memory for the rcu header structure +  the object.
435 * Returns the pointer to the object or NULL upon failure.
436 */
437void *ipc_rcu_alloc(int size)
438{
439	/*
440	 * We prepend the allocation with the rcu struct
441	 */
442	struct ipc_rcu *out = ipc_alloc(sizeof(struct ipc_rcu) + size);
443	if (unlikely(!out))
444		return NULL;
445	atomic_set(&out->refcount, 1);
446	return out + 1;
447}
448
449int ipc_rcu_getref(void *ptr)
450{
451	struct ipc_rcu *p = ((struct ipc_rcu *)ptr) - 1;
452
453	return atomic_inc_not_zero(&p->refcount);
454}
455
456void ipc_rcu_putref(void *ptr, void (*func)(struct rcu_head *head))
457{
458	struct ipc_rcu *p = ((struct ipc_rcu *)ptr) - 1;
459
460	if (!atomic_dec_and_test(&p->refcount))
461		return;
462
463	call_rcu(&p->rcu, func);
464}
465
466void ipc_rcu_free(struct rcu_head *head)
467{
468	struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu);
469
470	kvfree(p);
471}
472
473/**
474 * ipcperms - check ipc permissions
475 * @ns: ipc namespace
476 * @ipcp: ipc permission set
477 * @flag: desired permission set
478 *
479 * Check user, group, other permissions for access
480 * to ipc resources. return 0 if allowed
481 *
482 * @flag will most probably be 0 or S_...UGO from <linux/stat.h>
483 */
484int ipcperms(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp, short flag)
485{
486	kuid_t euid = current_euid();
487	int requested_mode, granted_mode;
488
489	audit_ipc_obj(ipcp);
490	requested_mode = (flag >> 6) | (flag >> 3) | flag;
491	granted_mode = ipcp->mode;
492	if (uid_eq(euid, ipcp->cuid) ||
493	    uid_eq(euid, ipcp->uid))
494		granted_mode >>= 6;
495	else if (in_group_p(ipcp->cgid) || in_group_p(ipcp->gid))
496		granted_mode >>= 3;
497	/* is there some bit set in requested_mode but not in granted_mode? */
498	if ((requested_mode & ~granted_mode & 0007) &&
499	    !ns_capable(ns->user_ns, CAP_IPC_OWNER))
500		return -1;
501
502	return security_ipc_permission(ipcp, flag);
503}
504
505/*
506 * Functions to convert between the kern_ipc_perm structure and the
507 * old/new ipc_perm structures
508 */
509
510/**
511 * kernel_to_ipc64_perm	- convert kernel ipc permissions to user
512 * @in: kernel permissions
513 * @out: new style ipc permissions
514 *
515 * Turn the kernel object @in into a set of permissions descriptions
516 * for returning to userspace (@out).
517 */
518void kernel_to_ipc64_perm(struct kern_ipc_perm *in, struct ipc64_perm *out)
519{
520	out->key	= in->key;
521	out->uid	= from_kuid_munged(current_user_ns(), in->uid);
522	out->gid	= from_kgid_munged(current_user_ns(), in->gid);
523	out->cuid	= from_kuid_munged(current_user_ns(), in->cuid);
524	out->cgid	= from_kgid_munged(current_user_ns(), in->cgid);
525	out->mode	= in->mode;
526	out->seq	= in->seq;
527}
528
529/**
530 * ipc64_perm_to_ipc_perm - convert new ipc permissions to old
531 * @in: new style ipc permissions
532 * @out: old style ipc permissions
533 *
534 * Turn the new style permissions object @in into a compatibility
535 * object and store it into the @out pointer.
536 */
537void ipc64_perm_to_ipc_perm(struct ipc64_perm *in, struct ipc_perm *out)
538{
539	out->key	= in->key;
540	SET_UID(out->uid, in->uid);
541	SET_GID(out->gid, in->gid);
542	SET_UID(out->cuid, in->cuid);
543	SET_GID(out->cgid, in->cgid);
544	out->mode	= in->mode;
545	out->seq	= in->seq;
546}
547
548/**
549 * ipc_obtain_object
550 * @ids: ipc identifier set
551 * @id: ipc id to look for
552 *
553 * Look for an id in the ipc ids idr and return associated ipc object.
554 *
555 * Call inside the RCU critical section.
556 * The ipc object is *not* locked on exit.
557 */
558struct kern_ipc_perm *ipc_obtain_object_idr(struct ipc_ids *ids, int id)
559{
560	struct kern_ipc_perm *out;
561	int lid = ipcid_to_idx(id);
562
563	out = idr_find(&ids->ipcs_idr, lid);
564	if (!out)
565		return ERR_PTR(-EINVAL);
566
567	return out;
568}
569
570/**
571 * ipc_lock - lock an ipc structure without rwsem held
572 * @ids: ipc identifier set
573 * @id: ipc id to look for
574 *
575 * Look for an id in the ipc ids idr and lock the associated ipc object.
576 *
577 * The ipc object is locked on successful exit.
578 */
579struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id)
580{
581	struct kern_ipc_perm *out;
582
583	rcu_read_lock();
584	out = ipc_obtain_object_idr(ids, id);
585	if (IS_ERR(out))
586		goto err;
587
588	spin_lock(&out->lock);
589
590	/*
591	 * ipc_rmid() may have already freed the ID while ipc_lock()
592	 * was spinning: here verify that the structure is still valid.
593	 * Upon races with RMID, return -EIDRM, thus indicating that
594	 * the ID points to a removed identifier.
595	 */
596	if (ipc_valid_object(out))
597		return out;
598
599	spin_unlock(&out->lock);
600	out = ERR_PTR(-EIDRM);
601err:
602	rcu_read_unlock();
603	return out;
604}
605
606/**
607 * ipc_obtain_object_check
608 * @ids: ipc identifier set
609 * @id: ipc id to look for
610 *
611 * Similar to ipc_obtain_object_idr() but also checks
612 * the ipc object reference counter.
613 *
614 * Call inside the RCU critical section.
615 * The ipc object is *not* locked on exit.
616 */
617struct kern_ipc_perm *ipc_obtain_object_check(struct ipc_ids *ids, int id)
618{
619	struct kern_ipc_perm *out = ipc_obtain_object_idr(ids, id);
620
621	if (IS_ERR(out))
622		goto out;
623
624	if (ipc_checkid(out, id))
625		return ERR_PTR(-EIDRM);
626out:
627	return out;
628}
629
630/**
631 * ipcget - Common sys_*get() code
632 * @ns: namespace
633 * @ids: ipc identifier set
634 * @ops: operations to be called on ipc object creation, permission checks
635 *       and further checks
636 * @params: the parameters needed by the previous operations.
637 *
638 * Common routine called by sys_msgget(), sys_semget() and sys_shmget().
639 */
640int ipcget(struct ipc_namespace *ns, struct ipc_ids *ids,
641			const struct ipc_ops *ops, struct ipc_params *params)
642{
643	if (params->key == IPC_PRIVATE)
644		return ipcget_new(ns, ids, ops, params);
645	else
646		return ipcget_public(ns, ids, ops, params);
647}
648
649/**
650 * ipc_update_perm - update the permissions of an ipc object
651 * @in:  the permission given as input.
652 * @out: the permission of the ipc to set.
653 */
654int ipc_update_perm(struct ipc64_perm *in, struct kern_ipc_perm *out)
655{
656	kuid_t uid = make_kuid(current_user_ns(), in->uid);
657	kgid_t gid = make_kgid(current_user_ns(), in->gid);
658	if (!uid_valid(uid) || !gid_valid(gid))
659		return -EINVAL;
660
661	out->uid = uid;
662	out->gid = gid;
663	out->mode = (out->mode & ~S_IRWXUGO)
664		| (in->mode & S_IRWXUGO);
665
666	return 0;
667}
668
669/**
670 * ipcctl_pre_down_nolock - retrieve an ipc and check permissions for some IPC_XXX cmd
671 * @ns:  ipc namespace
672 * @ids:  the table of ids where to look for the ipc
673 * @id:   the id of the ipc to retrieve
674 * @cmd:  the cmd to check
675 * @perm: the permission to set
676 * @extra_perm: one extra permission parameter used by msq
677 *
678 * This function does some common audit and permissions check for some IPC_XXX
679 * cmd and is called from semctl_down, shmctl_down and msgctl_down.
680 * It must be called without any lock held and
681 *  - retrieves the ipc with the given id in the given table.
682 *  - performs some audit and permission check, depending on the given cmd
683 *  - returns a pointer to the ipc object or otherwise, the corresponding error.
684 *
685 * Call holding the both the rwsem and the rcu read lock.
686 */
687struct kern_ipc_perm *ipcctl_pre_down_nolock(struct ipc_namespace *ns,
688					struct ipc_ids *ids, int id, int cmd,
689					struct ipc64_perm *perm, int extra_perm)
690{
691	kuid_t euid;
692	int err = -EPERM;
693	struct kern_ipc_perm *ipcp;
694
695	ipcp = ipc_obtain_object_check(ids, id);
696	if (IS_ERR(ipcp)) {
697		err = PTR_ERR(ipcp);
698		goto err;
699	}
700
701	audit_ipc_obj(ipcp);
702	if (cmd == IPC_SET)
703		audit_ipc_set_perm(extra_perm, perm->uid,
704				   perm->gid, perm->mode);
705
706	euid = current_euid();
707	if (uid_eq(euid, ipcp->cuid) || uid_eq(euid, ipcp->uid)  ||
708	    ns_capable(ns->user_ns, CAP_SYS_ADMIN))
709		return ipcp; /* successful lookup */
710err:
711	return ERR_PTR(err);
712}
713
714#ifdef CONFIG_ARCH_WANT_IPC_PARSE_VERSION
715
716
717/**
718 * ipc_parse_version - ipc call version
719 * @cmd: pointer to command
720 *
721 * Return IPC_64 for new style IPC and IPC_OLD for old style IPC.
722 * The @cmd value is turned from an encoding command and version into
723 * just the command code.
724 */
725int ipc_parse_version(int *cmd)
726{
727	if (*cmd & IPC_64) {
728		*cmd ^= IPC_64;
729		return IPC_64;
730	} else {
731		return IPC_OLD;
732	}
733}
734
735#endif /* CONFIG_ARCH_WANT_IPC_PARSE_VERSION */
736
737#ifdef CONFIG_PROC_FS
738struct ipc_proc_iter {
739	struct ipc_namespace *ns;
740	struct ipc_proc_iface *iface;
741};
742
743/*
744 * This routine locks the ipc structure found at least at position pos.
745 */
746static struct kern_ipc_perm *sysvipc_find_ipc(struct ipc_ids *ids, loff_t pos,
747					      loff_t *new_pos)
748{
749	struct kern_ipc_perm *ipc;
750	int total, id;
751
752	total = 0;
753	for (id = 0; id < pos && total < ids->in_use; id++) {
754		ipc = idr_find(&ids->ipcs_idr, id);
755		if (ipc != NULL)
756			total++;
757	}
758
759	if (total >= ids->in_use)
760		return NULL;
761
762	for (; pos < IPCMNI; pos++) {
763		ipc = idr_find(&ids->ipcs_idr, pos);
764		if (ipc != NULL) {
765			*new_pos = pos + 1;
766			rcu_read_lock();
767			ipc_lock_object(ipc);
768			return ipc;
769		}
770	}
771
772	/* Out of range - return NULL to terminate iteration */
773	return NULL;
774}
775
776static void *sysvipc_proc_next(struct seq_file *s, void *it, loff_t *pos)
777{
778	struct ipc_proc_iter *iter = s->private;
779	struct ipc_proc_iface *iface = iter->iface;
780	struct kern_ipc_perm *ipc = it;
781
782	/* If we had an ipc id locked before, unlock it */
783	if (ipc && ipc != SEQ_START_TOKEN)
784		ipc_unlock(ipc);
785
786	return sysvipc_find_ipc(&iter->ns->ids[iface->ids], *pos, pos);
787}
788
789/*
790 * File positions: pos 0 -> header, pos n -> ipc id = n - 1.
791 * SeqFile iterator: iterator value locked ipc pointer or SEQ_TOKEN_START.
792 */
793static void *sysvipc_proc_start(struct seq_file *s, loff_t *pos)
794{
795	struct ipc_proc_iter *iter = s->private;
796	struct ipc_proc_iface *iface = iter->iface;
797	struct ipc_ids *ids;
798
799	ids = &iter->ns->ids[iface->ids];
800
801	/*
802	 * Take the lock - this will be released by the corresponding
803	 * call to stop().
804	 */
805	down_read(&ids->rwsem);
806
807	/* pos < 0 is invalid */
808	if (*pos < 0)
809		return NULL;
810
811	/* pos == 0 means header */
812	if (*pos == 0)
813		return SEQ_START_TOKEN;
814
815	/* Find the (pos-1)th ipc */
816	return sysvipc_find_ipc(ids, *pos - 1, pos);
817}
818
819static void sysvipc_proc_stop(struct seq_file *s, void *it)
820{
821	struct kern_ipc_perm *ipc = it;
822	struct ipc_proc_iter *iter = s->private;
823	struct ipc_proc_iface *iface = iter->iface;
824	struct ipc_ids *ids;
825
826	/* If we had a locked structure, release it */
827	if (ipc && ipc != SEQ_START_TOKEN)
828		ipc_unlock(ipc);
829
830	ids = &iter->ns->ids[iface->ids];
831	/* Release the lock we took in start() */
832	up_read(&ids->rwsem);
833}
834
835static int sysvipc_proc_show(struct seq_file *s, void *it)
836{
837	struct ipc_proc_iter *iter = s->private;
838	struct ipc_proc_iface *iface = iter->iface;
839
840	if (it == SEQ_START_TOKEN) {
841		seq_puts(s, iface->header);
842		return 0;
843	}
844
845	return iface->show(s, it);
846}
847
848static const struct seq_operations sysvipc_proc_seqops = {
849	.start = sysvipc_proc_start,
850	.stop  = sysvipc_proc_stop,
851	.next  = sysvipc_proc_next,
852	.show  = sysvipc_proc_show,
853};
854
855static int sysvipc_proc_open(struct inode *inode, struct file *file)
856{
857	struct ipc_proc_iter *iter;
858
859	iter = __seq_open_private(file, &sysvipc_proc_seqops, sizeof(*iter));
860	if (!iter)
861		return -ENOMEM;
862
863	iter->iface = PDE_DATA(inode);
864	iter->ns    = get_ipc_ns(current->nsproxy->ipc_ns);
865
866	return 0;
867}
868
869static int sysvipc_proc_release(struct inode *inode, struct file *file)
870{
871	struct seq_file *seq = file->private_data;
872	struct ipc_proc_iter *iter = seq->private;
873	put_ipc_ns(iter->ns);
874	return seq_release_private(inode, file);
875}
876
877static const struct file_operations sysvipc_proc_fops = {
878	.open    = sysvipc_proc_open,
879	.read    = seq_read,
880	.llseek  = seq_lseek,
881	.release = sysvipc_proc_release,
882};
883#endif /* CONFIG_PROC_FS */
884