util.c revision 1d5cfdb0
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	current_euid_egid(&euid, &egid);
241	new->cuid = new->uid = euid;
242	new->gid = new->cgid = egid;
243
244	id = idr_alloc(&ids->ipcs_idr, new,
245		       (next_id < 0) ? 0 : ipcid_to_idx(next_id), 0,
246		       GFP_NOWAIT);
247	idr_preload_end();
248	if (id < 0) {
249		spin_unlock(&new->lock);
250		rcu_read_unlock();
251		return id;
252	}
253
254	ids->in_use++;
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 *
418 * Free a block created with ipc_alloc().
419 */
420void ipc_free(void *ptr)
421{
422	kvfree(ptr);
423}
424
425/**
426 * ipc_rcu_alloc - allocate ipc and rcu space
427 * @size: size desired
428 *
429 * Allocate memory for the rcu header structure +  the object.
430 * Returns the pointer to the object or NULL upon failure.
431 */
432void *ipc_rcu_alloc(int size)
433{
434	/*
435	 * We prepend the allocation with the rcu struct
436	 */
437	struct ipc_rcu *out = ipc_alloc(sizeof(struct ipc_rcu) + size);
438	if (unlikely(!out))
439		return NULL;
440	atomic_set(&out->refcount, 1);
441	return out + 1;
442}
443
444int ipc_rcu_getref(void *ptr)
445{
446	struct ipc_rcu *p = ((struct ipc_rcu *)ptr) - 1;
447
448	return atomic_inc_not_zero(&p->refcount);
449}
450
451void ipc_rcu_putref(void *ptr, void (*func)(struct rcu_head *head))
452{
453	struct ipc_rcu *p = ((struct ipc_rcu *)ptr) - 1;
454
455	if (!atomic_dec_and_test(&p->refcount))
456		return;
457
458	call_rcu(&p->rcu, func);
459}
460
461void ipc_rcu_free(struct rcu_head *head)
462{
463	struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu);
464
465	kvfree(p);
466}
467
468/**
469 * ipcperms - check ipc permissions
470 * @ns: ipc namespace
471 * @ipcp: ipc permission set
472 * @flag: desired permission set
473 *
474 * Check user, group, other permissions for access
475 * to ipc resources. return 0 if allowed
476 *
477 * @flag will most probably be 0 or S_...UGO from <linux/stat.h>
478 */
479int ipcperms(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp, short flag)
480{
481	kuid_t euid = current_euid();
482	int requested_mode, granted_mode;
483
484	audit_ipc_obj(ipcp);
485	requested_mode = (flag >> 6) | (flag >> 3) | flag;
486	granted_mode = ipcp->mode;
487	if (uid_eq(euid, ipcp->cuid) ||
488	    uid_eq(euid, ipcp->uid))
489		granted_mode >>= 6;
490	else if (in_group_p(ipcp->cgid) || in_group_p(ipcp->gid))
491		granted_mode >>= 3;
492	/* is there some bit set in requested_mode but not in granted_mode? */
493	if ((requested_mode & ~granted_mode & 0007) &&
494	    !ns_capable(ns->user_ns, CAP_IPC_OWNER))
495		return -1;
496
497	return security_ipc_permission(ipcp, flag);
498}
499
500/*
501 * Functions to convert between the kern_ipc_perm structure and the
502 * old/new ipc_perm structures
503 */
504
505/**
506 * kernel_to_ipc64_perm	- convert kernel ipc permissions to user
507 * @in: kernel permissions
508 * @out: new style ipc permissions
509 *
510 * Turn the kernel object @in into a set of permissions descriptions
511 * for returning to userspace (@out).
512 */
513void kernel_to_ipc64_perm(struct kern_ipc_perm *in, struct ipc64_perm *out)
514{
515	out->key	= in->key;
516	out->uid	= from_kuid_munged(current_user_ns(), in->uid);
517	out->gid	= from_kgid_munged(current_user_ns(), in->gid);
518	out->cuid	= from_kuid_munged(current_user_ns(), in->cuid);
519	out->cgid	= from_kgid_munged(current_user_ns(), in->cgid);
520	out->mode	= in->mode;
521	out->seq	= in->seq;
522}
523
524/**
525 * ipc64_perm_to_ipc_perm - convert new ipc permissions to old
526 * @in: new style ipc permissions
527 * @out: old style ipc permissions
528 *
529 * Turn the new style permissions object @in into a compatibility
530 * object and store it into the @out pointer.
531 */
532void ipc64_perm_to_ipc_perm(struct ipc64_perm *in, struct ipc_perm *out)
533{
534	out->key	= in->key;
535	SET_UID(out->uid, in->uid);
536	SET_GID(out->gid, in->gid);
537	SET_UID(out->cuid, in->cuid);
538	SET_GID(out->cgid, in->cgid);
539	out->mode	= in->mode;
540	out->seq	= in->seq;
541}
542
543/**
544 * ipc_obtain_object
545 * @ids: ipc identifier set
546 * @id: ipc id to look for
547 *
548 * Look for an id in the ipc ids idr and return associated ipc object.
549 *
550 * Call inside the RCU critical section.
551 * The ipc object is *not* locked on exit.
552 */
553struct kern_ipc_perm *ipc_obtain_object_idr(struct ipc_ids *ids, int id)
554{
555	struct kern_ipc_perm *out;
556	int lid = ipcid_to_idx(id);
557
558	out = idr_find(&ids->ipcs_idr, lid);
559	if (!out)
560		return ERR_PTR(-EINVAL);
561
562	return out;
563}
564
565/**
566 * ipc_lock - lock an ipc structure without rwsem held
567 * @ids: ipc identifier set
568 * @id: ipc id to look for
569 *
570 * Look for an id in the ipc ids idr and lock the associated ipc object.
571 *
572 * The ipc object is locked on successful exit.
573 */
574struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id)
575{
576	struct kern_ipc_perm *out;
577
578	rcu_read_lock();
579	out = ipc_obtain_object_idr(ids, id);
580	if (IS_ERR(out))
581		goto err;
582
583	spin_lock(&out->lock);
584
585	/*
586	 * ipc_rmid() may have already freed the ID while ipc_lock()
587	 * was spinning: here verify that the structure is still valid.
588	 * Upon races with RMID, return -EIDRM, thus indicating that
589	 * the ID points to a removed identifier.
590	 */
591	if (ipc_valid_object(out))
592		return out;
593
594	spin_unlock(&out->lock);
595	out = ERR_PTR(-EIDRM);
596err:
597	rcu_read_unlock();
598	return out;
599}
600
601/**
602 * ipc_obtain_object_check
603 * @ids: ipc identifier set
604 * @id: ipc id to look for
605 *
606 * Similar to ipc_obtain_object_idr() but also checks
607 * the ipc object reference counter.
608 *
609 * Call inside the RCU critical section.
610 * The ipc object is *not* locked on exit.
611 */
612struct kern_ipc_perm *ipc_obtain_object_check(struct ipc_ids *ids, int id)
613{
614	struct kern_ipc_perm *out = ipc_obtain_object_idr(ids, id);
615
616	if (IS_ERR(out))
617		goto out;
618
619	if (ipc_checkid(out, id))
620		return ERR_PTR(-EINVAL);
621out:
622	return out;
623}
624
625/**
626 * ipcget - Common sys_*get() code
627 * @ns: namespace
628 * @ids: ipc identifier set
629 * @ops: operations to be called on ipc object creation, permission checks
630 *       and further checks
631 * @params: the parameters needed by the previous operations.
632 *
633 * Common routine called by sys_msgget(), sys_semget() and sys_shmget().
634 */
635int ipcget(struct ipc_namespace *ns, struct ipc_ids *ids,
636			const struct ipc_ops *ops, struct ipc_params *params)
637{
638	if (params->key == IPC_PRIVATE)
639		return ipcget_new(ns, ids, ops, params);
640	else
641		return ipcget_public(ns, ids, ops, params);
642}
643
644/**
645 * ipc_update_perm - update the permissions of an ipc object
646 * @in:  the permission given as input.
647 * @out: the permission of the ipc to set.
648 */
649int ipc_update_perm(struct ipc64_perm *in, struct kern_ipc_perm *out)
650{
651	kuid_t uid = make_kuid(current_user_ns(), in->uid);
652	kgid_t gid = make_kgid(current_user_ns(), in->gid);
653	if (!uid_valid(uid) || !gid_valid(gid))
654		return -EINVAL;
655
656	out->uid = uid;
657	out->gid = gid;
658	out->mode = (out->mode & ~S_IRWXUGO)
659		| (in->mode & S_IRWXUGO);
660
661	return 0;
662}
663
664/**
665 * ipcctl_pre_down_nolock - retrieve an ipc and check permissions for some IPC_XXX cmd
666 * @ns:  ipc namespace
667 * @ids:  the table of ids where to look for the ipc
668 * @id:   the id of the ipc to retrieve
669 * @cmd:  the cmd to check
670 * @perm: the permission to set
671 * @extra_perm: one extra permission parameter used by msq
672 *
673 * This function does some common audit and permissions check for some IPC_XXX
674 * cmd and is called from semctl_down, shmctl_down and msgctl_down.
675 * It must be called without any lock held and
676 *  - retrieves the ipc with the given id in the given table.
677 *  - performs some audit and permission check, depending on the given cmd
678 *  - returns a pointer to the ipc object or otherwise, the corresponding error.
679 *
680 * Call holding the both the rwsem and the rcu read lock.
681 */
682struct kern_ipc_perm *ipcctl_pre_down_nolock(struct ipc_namespace *ns,
683					struct ipc_ids *ids, int id, int cmd,
684					struct ipc64_perm *perm, int extra_perm)
685{
686	kuid_t euid;
687	int err = -EPERM;
688	struct kern_ipc_perm *ipcp;
689
690	ipcp = ipc_obtain_object_check(ids, id);
691	if (IS_ERR(ipcp)) {
692		err = PTR_ERR(ipcp);
693		goto err;
694	}
695
696	audit_ipc_obj(ipcp);
697	if (cmd == IPC_SET)
698		audit_ipc_set_perm(extra_perm, perm->uid,
699				   perm->gid, perm->mode);
700
701	euid = current_euid();
702	if (uid_eq(euid, ipcp->cuid) || uid_eq(euid, ipcp->uid)  ||
703	    ns_capable(ns->user_ns, CAP_SYS_ADMIN))
704		return ipcp; /* successful lookup */
705err:
706	return ERR_PTR(err);
707}
708
709#ifdef CONFIG_ARCH_WANT_IPC_PARSE_VERSION
710
711
712/**
713 * ipc_parse_version - ipc call version
714 * @cmd: pointer to command
715 *
716 * Return IPC_64 for new style IPC and IPC_OLD for old style IPC.
717 * The @cmd value is turned from an encoding command and version into
718 * just the command code.
719 */
720int ipc_parse_version(int *cmd)
721{
722	if (*cmd & IPC_64) {
723		*cmd ^= IPC_64;
724		return IPC_64;
725	} else {
726		return IPC_OLD;
727	}
728}
729
730#endif /* CONFIG_ARCH_WANT_IPC_PARSE_VERSION */
731
732#ifdef CONFIG_PROC_FS
733struct ipc_proc_iter {
734	struct ipc_namespace *ns;
735	struct ipc_proc_iface *iface;
736};
737
738/*
739 * This routine locks the ipc structure found at least at position pos.
740 */
741static struct kern_ipc_perm *sysvipc_find_ipc(struct ipc_ids *ids, loff_t pos,
742					      loff_t *new_pos)
743{
744	struct kern_ipc_perm *ipc;
745	int total, id;
746
747	total = 0;
748	for (id = 0; id < pos && total < ids->in_use; id++) {
749		ipc = idr_find(&ids->ipcs_idr, id);
750		if (ipc != NULL)
751			total++;
752	}
753
754	if (total >= ids->in_use)
755		return NULL;
756
757	for (; pos < IPCMNI; pos++) {
758		ipc = idr_find(&ids->ipcs_idr, pos);
759		if (ipc != NULL) {
760			*new_pos = pos + 1;
761			rcu_read_lock();
762			ipc_lock_object(ipc);
763			return ipc;
764		}
765	}
766
767	/* Out of range - return NULL to terminate iteration */
768	return NULL;
769}
770
771static void *sysvipc_proc_next(struct seq_file *s, void *it, loff_t *pos)
772{
773	struct ipc_proc_iter *iter = s->private;
774	struct ipc_proc_iface *iface = iter->iface;
775	struct kern_ipc_perm *ipc = it;
776
777	/* If we had an ipc id locked before, unlock it */
778	if (ipc && ipc != SEQ_START_TOKEN)
779		ipc_unlock(ipc);
780
781	return sysvipc_find_ipc(&iter->ns->ids[iface->ids], *pos, pos);
782}
783
784/*
785 * File positions: pos 0 -> header, pos n -> ipc id = n - 1.
786 * SeqFile iterator: iterator value locked ipc pointer or SEQ_TOKEN_START.
787 */
788static void *sysvipc_proc_start(struct seq_file *s, loff_t *pos)
789{
790	struct ipc_proc_iter *iter = s->private;
791	struct ipc_proc_iface *iface = iter->iface;
792	struct ipc_ids *ids;
793
794	ids = &iter->ns->ids[iface->ids];
795
796	/*
797	 * Take the lock - this will be released by the corresponding
798	 * call to stop().
799	 */
800	down_read(&ids->rwsem);
801
802	/* pos < 0 is invalid */
803	if (*pos < 0)
804		return NULL;
805
806	/* pos == 0 means header */
807	if (*pos == 0)
808		return SEQ_START_TOKEN;
809
810	/* Find the (pos-1)th ipc */
811	return sysvipc_find_ipc(ids, *pos - 1, pos);
812}
813
814static void sysvipc_proc_stop(struct seq_file *s, void *it)
815{
816	struct kern_ipc_perm *ipc = it;
817	struct ipc_proc_iter *iter = s->private;
818	struct ipc_proc_iface *iface = iter->iface;
819	struct ipc_ids *ids;
820
821	/* If we had a locked structure, release it */
822	if (ipc && ipc != SEQ_START_TOKEN)
823		ipc_unlock(ipc);
824
825	ids = &iter->ns->ids[iface->ids];
826	/* Release the lock we took in start() */
827	up_read(&ids->rwsem);
828}
829
830static int sysvipc_proc_show(struct seq_file *s, void *it)
831{
832	struct ipc_proc_iter *iter = s->private;
833	struct ipc_proc_iface *iface = iter->iface;
834
835	if (it == SEQ_START_TOKEN) {
836		seq_puts(s, iface->header);
837		return 0;
838	}
839
840	return iface->show(s, it);
841}
842
843static const struct seq_operations sysvipc_proc_seqops = {
844	.start = sysvipc_proc_start,
845	.stop  = sysvipc_proc_stop,
846	.next  = sysvipc_proc_next,
847	.show  = sysvipc_proc_show,
848};
849
850static int sysvipc_proc_open(struct inode *inode, struct file *file)
851{
852	struct ipc_proc_iter *iter;
853
854	iter = __seq_open_private(file, &sysvipc_proc_seqops, sizeof(*iter));
855	if (!iter)
856		return -ENOMEM;
857
858	iter->iface = PDE_DATA(inode);
859	iter->ns    = get_ipc_ns(current->nsproxy->ipc_ns);
860
861	return 0;
862}
863
864static int sysvipc_proc_release(struct inode *inode, struct file *file)
865{
866	struct seq_file *seq = file->private_data;
867	struct ipc_proc_iter *iter = seq->private;
868	put_ipc_ns(iter->ns);
869	return seq_release_private(inode, file);
870}
871
872static const struct file_operations sysvipc_proc_fops = {
873	.open    = sysvipc_proc_open,
874	.read    = seq_read,
875	.llseek  = seq_lseek,
876	.release = sysvipc_proc_release,
877};
878#endif /* CONFIG_PROC_FS */
879