summaryrefslogtreecommitdiffstats
path: root/ipc/msg.c
blob: 2b4fccf8ea55a9a2babc5f92b36fcdf6a1dd5a7d (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
/*
 * linux/ipc/msg.c
 * Copyright (C) 1992 Krishna Balasubramanian
 *
 * Removed all the remaining kerneld mess
 * Catch the -EFAULT stuff properly
 * Use GFP_KERNEL for messages as in 1.2
 * Fixed up the unchecked user space derefs
 * Copyright (C) 1998 Alan Cox & Andi Kleen
 *
 * /proc/sysvipc/msg support (c) 1999 Dragos Acostachioaie <dragos@iname.com>
 *
 * mostly rewritten, threaded and wake-one semantics added
 * MSGMAX limit removed, sysctl's added
 * (c) 1999 Manfred Spraul <manfred@colorfullife.com>
 *
 * support for audit of ipc object properties and permission changes
 * Dustin Kirkland <dustin.kirkland@us.ibm.com>
 */

#include <linux/capability.h>
#include <linux/slab.h>
#include <linux/msg.h>
#include <linux/spinlock.h>
#include <linux/init.h>
#include <linux/proc_fs.h>
#include <linux/list.h>
#include <linux/security.h>
#include <linux/sched.h>
#include <linux/syscalls.h>
#include <linux/audit.h>
#include <linux/seq_file.h>
#include <linux/mutex.h>

#include <asm/current.h>
#include <asm/uaccess.h>
#include "util.h"

/* sysctl: */
int msg_ctlmax = MSGMAX;
int msg_ctlmnb = MSGMNB;
int msg_ctlmni = MSGMNI;

/*
 * one msg_receiver structure for each sleeping receiver:
 */
struct msg_receiver {
	struct list_head	r_list;
	struct task_struct	*r_tsk;

	int			r_mode;
	long			r_msgtype;
	long			r_maxsize;

	volatile struct msg_msg	*r_msg;
};

/* one msg_sender for each sleeping sender */
struct msg_sender {
	struct list_head	list;
	struct task_struct	*tsk;
};

#define SEARCH_ANY		1
#define SEARCH_EQUAL		2
#define SEARCH_NOTEQUAL		3
#define SEARCH_LESSEQUAL	4

static atomic_t msg_bytes =	ATOMIC_INIT(0);
static atomic_t msg_hdrs =	ATOMIC_INIT(0);

static struct ipc_ids msg_ids;

#define msg_lock(id)		((struct msg_queue *)ipc_lock(&msg_ids, id))
#define msg_unlock(msq)		ipc_unlock(&(msq)->q_perm)
#define msg_rmid(id)		((struct msg_queue *)ipc_rmid(&msg_ids, id))
#define msg_checkid(msq, msgid)	ipc_checkid(&msg_ids, &msq->q_perm, msgid)
#define msg_buildid(id, seq)	ipc_buildid(&msg_ids, id, seq)

static void freeque(struct msg_queue *msq, int id);
static int newque(key_t key, int msgflg);
#ifdef CONFIG_PROC_FS
static int sysvipc_msg_proc_show(struct seq_file *s, void *it);
#endif

void __init msg_init(void)
{
	ipc_init_ids(&msg_ids, msg_ctlmni);
	ipc_init_proc_interface("sysvipc/msg",
				"       key      msqid perms      cbytes       qnum lspid lrpid   uid   gid  cuid  cgid      stime      rtime      ctime\n",
				&msg_ids,
				sysvipc_msg_proc_show);
}

static int newque(key_t key, int msgflg)
{
	struct msg_queue *msq;
	int id, retval;

	msq = ipc_rcu_alloc(sizeof(*msq));
	if (!msq)
		return -ENOMEM;

	msq->q_perm.mode = msgflg & S_IRWXUGO;
	msq->q_perm.key = key;

	msq->q_perm.security = NULL;
	retval = security_msg_queue_alloc(msq);
	if (retval) {
		ipc_rcu_putref(msq);
		return retval;
	}

	id = ipc_addid(&msg_ids, &msq->q_perm, msg_ctlmni);
	if (id == -1) {
		security_msg_queue_free(msq);
		ipc_rcu_putref(msq);
		return -ENOSPC;
	}

	msq->q_id = msg_buildid(id, msq->q_perm.seq);
	msq->q_stime = msq->q_rtime = 0;
	msq->q_ctime = get_seconds();
	msq->q_cbytes = msq->q_qnum = 0;
	msq->q_qbytes = msg_ctlmnb;
	msq->q_lspid = msq->q_lrpid = 0;
	INIT_LIST_HEAD(&msq->q_messages);
	INIT_LIST_HEAD(&msq->q_receivers);
	INIT_LIST_HEAD(&msq->q_senders);
	msg_unlock(msq);

	return msq->q_id;
}

static inline void ss_add(struct msg_queue *msq, struct msg_sender *mss)
{
	mss->tsk = current;
	current->state = TASK_INTERRUPTIBLE;
	list_add_tail(&mss->list, &msq->q_senders);
}

static inline void ss_del(struct msg_sender *mss)
{
	if (mss->list.next != NULL)
		list_del(&mss->list);
}

static void ss_wakeup(struct list_head *h, int kill)
{
	struct list_head *tmp;

	tmp = h->next;
	while (tmp != h) {
		struct msg_sender *mss;

		mss = list_entry(tmp, struct msg_sender, list);
		tmp = tmp->next;
		if (kill)
			mss->list.next = NULL;
		wake_up_process(mss->tsk);
	}
}

static void expunge_all(struct msg_queue *msq, int res)
{
	struct list_head *tmp;

	tmp = msq->q_receivers.next;
	while (tmp != &msq->q_receivers) {
		struct msg_receiver *msr;

		msr = list_entry(tmp, struct msg_receiver, r_list);
		tmp = tmp->next;
		msr->r_msg = NULL;
		wake_up_process(msr->r_tsk);
		smp_mb();
		msr->r_msg = ERR_PTR(res);
	}
}

/*
 * freeque() wakes up waiters on the sender and receiver waiting queue,
 * removes the message queue from message queue ID
 * array, and cleans up all the messages associated with this queue.
 *
 * msg_ids.mutex and the spinlock for this message queue is hold
 * before freeque() is called. msg_ids.mutex remains locked on exit.
 */
static void freeque(struct msg_queue *msq, int id)
{
	struct list_head *tmp;

	expunge_all(msq, -EIDRM);
	ss_wakeup(&msq->q_senders, 1);
	msq = msg_rmid(id);
	msg_unlock(msq);

	tmp = msq->q_messages.next;
	while (tmp != &msq->q_messages) {
		struct msg_msg *msg = list_entry(tmp, struct msg_msg, m_list);

		tmp = tmp->next;
		atomic_dec(&msg_hdrs);
		free_msg(msg);
	}
	atomic_sub(msq->q_cbytes, &msg_bytes);
	security_msg_queue_free(msq);
	ipc_rcu_putref(msq);
}

asmlinkage long sys_msgget(key_t key, int msgflg)
{
	struct msg_queue *msq;
	int id, ret = -EPERM;
	
	mutex_lock(&msg_ids.mutex);
	if (key == IPC_PRIVATE) 
		ret = newque(key, msgflg);
	else if ((id = ipc_findkey(&msg_ids, key)) == -1) { /* key not used */
		if (!(msgflg & IPC_CREAT))
			ret = -ENOENT;
		else
			ret = newque(key, msgflg);
	} else if (msgflg & IPC_CREAT && msgflg & IPC_EXCL) {
		ret = -EEXIST;
	} else {
		msq = msg_lock(id);
		BUG_ON(msq == NULL);
		if (ipcperms(&msq->q_perm, msgflg))
			ret = -EACCES;
		else {
			int qid = msg_buildid(id, msq->q_perm.seq);

			ret = security_msg_queue_associate(msq, msgflg);
			if (!ret)
				ret = qid;
		}
		msg_unlock(msq);
	}
	mutex_unlock(&msg_ids.mutex);

	return ret;
}

static inline unsigned long
copy_msqid_to_user(void __user *buf, struct msqid64_ds *in, int version)
{
	switch(version) {
	case IPC_64:
		return copy_to_user(buf, in, sizeof(*in));
	case IPC_OLD:
	{
		struct msqid_ds out;

		memset(&out, 0, sizeof(out));

		ipc64_perm_to_ipc_perm(&in->msg_perm, &out.msg_perm);

		out.msg_stime		= in->msg_stime;
		out.msg_rtime		= in->msg_rtime;
		out.msg_ctime		= in->msg_ctime;

		if (in->msg_cbytes > USHRT_MAX)
			out.msg_cbytes	= USHRT_MAX;
		else
			out.msg_cbytes	= in->msg_cbytes;
		out.msg_lcbytes		= in->msg_cbytes;

		if (in->msg_qnum > USHRT_MAX)
			out.msg_qnum	= USHRT_MAX;
		else
			out.msg_qnum	= in->msg_qnum;

		if (in->msg_qbytes > USHRT_MAX)
			out.msg_qbytes	= USHRT_MAX;
		else
			out.msg_qbytes	= in->msg_qbytes;
		out.msg_lqbytes		= in->msg_qbytes;

		out.msg_lspid		= in->msg_lspid;
		out.msg_lrpid		= in->msg_lrpid;

		return copy_to_user(buf, &out, sizeof(out));
	}
	default:
		return -EINVAL;
	}
}

struct msq_setbuf {
	unsigned long	qbytes;
	uid_t		uid;
	gid_t		gid;
	mode_t		mode;
};

static inline unsigned long
copy_msqid_from_user(struct msq_setbuf *out, void __user *buf, int version)
{
	switch(version) {
	case IPC_64:
	{
		struct msqid64_ds tbuf;

		if (copy_from_user(&tbuf, buf, sizeof(tbuf)))
			return -EFAULT;

		out->qbytes		= tbuf.msg_qbytes;
		out->uid		= tbuf.msg_perm.uid;
		out->gid		= tbuf.msg_perm.gid;
		out->mode		= tbuf.msg_perm.mode;

		return 0;
	}
	case IPC_OLD:
	{
		struct msqid_ds tbuf_old;

		if (copy_from_user(&tbuf_old, buf, sizeof(tbuf_old)))
			return -EFAULT;

		out->uid		= tbuf_old.msg_perm.uid;
		out->gid		= tbuf_old.msg_perm.gid;
		out->mode		= tbuf_old.msg_perm.mode;

		if (tbuf_old.msg_qbytes == 0)
			out->qbytes	= tbuf_old.msg_lqbytes;
		else
			out->qbytes	= tbuf_old.msg_qbytes;

		return 0;
	}
	default:
		return -EINVAL;
	}
}

asmlinkage long sys_msgctl(int msqid, int cmd, struct msqid_ds __user *buf)
{
	struct kern_ipc_perm *ipcp;
	struct msq_setbuf setbuf;
	struct msg_queue *msq;
	int err, version;

	if (msqid < 0 || cmd < 0)
		return -EINVAL;

	version = ipc_parse_version(&cmd);

	switch (cmd) {
	case IPC_INFO:
	case MSG_INFO:
	{
		struct msginfo msginfo;
		int max_id;

		if (!buf)
			return -EFAULT;
		/*
		 * We must not return kernel stack data.
		 * due to padding, it's not enough
		 * to set all member fields.
		 */
		err = security_msg_queue_msgctl(NULL, cmd);
		if (err)
			return err;

		memset(&msginfo, 0, sizeof(msginfo));
		msginfo.msgmni = msg_ctlmni;
		msginfo.msgmax = msg_ctlmax;
		msginfo.msgmnb = msg_ctlmnb;
		msginfo.msgssz = MSGSSZ;
		msginfo.msgseg = MSGSEG;
		mutex_lock(&msg_ids.mutex);
		if (cmd == MSG_INFO) {
			msginfo.msgpool = msg_ids.in_use;
			msginfo.msgmap = atomic_read(&msg_hdrs);
			msginfo.msgtql = atomic_read(&msg_bytes);
		} else {
			msginfo.msgmap = MSGMAP;
			msginfo.msgpool = MSGPOOL;
			msginfo.msgtql = MSGTQL;
		}
		max_id = msg_ids.max_id;
		mutex_unlock(&msg_ids.mutex);
		if (copy_to_user(buf, &msginfo, sizeof(struct msginfo)))
			return -EFAULT;
		return (max_id < 0) ? 0 : max_id;
	}
	case MSG_STAT:
	case IPC_STAT:
	{
		struct msqid64_ds tbuf;
		int success_return;

		if (!buf)
			return -EFAULT;
		if (cmd == MSG_STAT && msqid >= msg_ids.entries->size)
			return -EINVAL;

		memset(&tbuf, 0, sizeof(tbuf));

		msq = msg_lock(msqid);
		if (msq == NULL)
			return -EINVAL;

		if (cmd == MSG_STAT) {
			success_return = msg_buildid(msqid, msq->q_perm.seq);
		} else {
			err = -EIDRM;
			if (msg_checkid(msq, msqid))
				goto out_unlock;
			success_return = 0;
		}
		err = -EACCES;
		if (ipcperms(&msq->q_perm, S_IRUGO))
			goto out_unlock;

		err = security_msg_queue_msgctl(msq, cmd);
		if (err)
			goto out_unlock;

		kernel_to_ipc64_perm(&msq->q_perm, &tbuf.msg_perm);
		tbuf.msg_stime  = msq->q_stime;
		tbuf.msg_rtime  = msq->q_rtime;
		tbuf.msg_ctime  = msq->q_ctime;
		tbuf.msg_cbytes = msq->q_cbytes;
		tbuf.msg_qnum   = msq->q_qnum;
		tbuf.msg_qbytes = msq->q_qbytes;
		tbuf.msg_lspid  = msq->q_lspid;
		tbuf.msg_lrpid  = msq->q_lrpid;
		msg_unlock(msq);
		if (copy_msqid_to_user(buf, &tbuf, version))
			return -EFAULT;
		return success_return;
	}
	case IPC_SET:
		if (!buf)
			return -EFAULT;
		if (copy_msqid_from_user(&setbuf, buf, version))
			return -EFAULT;
		break;
	case IPC_RMID:
		break;
	default:
		return  -EINVAL;
	}

	mutex_lock(&msg_ids.mutex);
	msq = msg_lock(msqid);
	err = -EINVAL;
	if (msq == NULL)
		goto out_up;

	err = -EIDRM;
	if (msg_checkid(msq, msqid))
		goto out_unlock_up;
	ipcp = &msq->q_perm;

	err = audit_ipc_obj(ipcp);
	if (err)
		goto out_unlock_up;
	if (cmd==IPC_SET) {
		err = audit_ipc_set_perm(setbuf.qbytes, setbuf.uid, setbuf.gid,
					 setbuf.mode);
		if (err)
			goto out_unlock_up;
	}

	err = -EPERM;
	if (current->euid != ipcp->cuid &&
	    current->euid != ipcp->uid && !capable(CAP_SYS_ADMIN))
		/* We _could_ check for CAP_CHOWN above, but we don't */
		goto out_unlock_up;

	err = security_msg_queue_msgctl(msq, cmd);
	if (err)
		goto out_unlock_up;

	switch (cmd) {
	case IPC_SET:
	{
		err = -EPERM;
		if (setbuf.qbytes > msg_ctlmnb && !capable(CAP_SYS_RESOURCE))
			goto out_unlock_up;

		msq->q_qbytes = setbuf.qbytes;

		ipcp->uid = setbuf.uid;
		ipcp->gid = setbuf.gid;
		ipcp->mode = (ipcp->mode & ~S_IRWXUGO) |
			     (S_IRWXUGO & setbuf.mode);
		msq->q_ctime = get_seconds();
		/* sleeping receivers might be excluded by
		 * stricter permissions.
		 */
		expunge_all(msq, -EAGAIN);
		/* sleeping senders might be able to send
		 * due to a larger queue size.
		 */
		ss_wakeup(&msq->q_senders, 0);
		msg_unlock(msq);
		break;
	}
	case IPC_RMID:
		freeque(msq, msqid);
		break;
	}
	err = 0;
out_up:
	mutex_unlock(&msg_ids.mutex);
	return err;
out_unlock_up:
	msg_unlock(msq);
	goto out_up;
out_unlock:
	msg_unlock(msq);
	return err;
}

static int testmsg(struct msg_msg *msg, long type, int mode)
{
	switch(mode)
	{
		case SEARCH_ANY:
			return 1;
		case SEARCH_LESSEQUAL:
			if (msg->m_type <=type)
				return 1;
			break;
		case SEARCH_EQUAL:
			if (msg->m_type == type)
				return 1;
			break;
		case SEARCH_NOTEQUAL:
			if (msg->m_type != type)
				return 1;
			break;
	}
	return 0;
}

static inline int pipelined_send(struct msg_queue *msq, struct msg_msg *msg)
{
	struct list_head *tmp;

	tmp = msq->q_receivers.next;
	while (tmp != &msq->q_receivers) {
		struct msg_receiver *msr;

		msr = list_entry(tmp, struct msg_receiver, r_list);
		tmp = tmp->next;
		if (testmsg(msg, msr->r_msgtype, msr->r_mode) &&
		    !security_msg_queue_msgrcv(msq, msg, msr->r_tsk,
					       msr->r_msgtype, msr->r_mode)) {

			list_del(&msr->r_list);
			if (msr->r_maxsize < msg->m_ts) {
				msr->r_msg = NULL;
				wake_up_process(msr->r_tsk);
				smp_mb();
				msr->r_msg = ERR_PTR(-E2BIG);
			} else {
				msr->r_msg = NULL;
				msq->q_lrpid = msr->r_tsk->pid;
				msq->q_rtime = get_seconds();
				wake_up_process(msr->r_tsk);
				smp_mb();
				msr->r_msg = msg;

				return 1;
			}
		}
	}
	return 0;
}

asmlinkage long
sys_msgsnd(int msqid, struct msgbuf __user *msgp, size_t msgsz, int msgflg)
{
	struct msg_queue *msq;
	struct msg_msg *msg;
	long mtype;
	int err;

	if (msgsz > msg_ctlmax || (long) msgsz < 0 || msqid < 0)
		return -EINVAL;
	if (get_user(mtype, &msgp->mtype))
		return -EFAULT;
	if (mtype < 1)
		return -EINVAL;

	msg = load_msg(msgp->mtext, msgsz);
	if (IS_ERR(msg))
		return PTR_ERR(msg);

	msg->m_type = mtype;
	msg->m_ts = msgsz;

	msq = msg_lock(msqid);
	err = -EINVAL;
	if (msq == NULL)
		goto out_free;

	err= -EIDRM;
	if (msg_checkid(msq, msqid))
		goto out_unlock_free;

	for (;;) {
		struct msg_sender s;

		err = -EACCES;
		if (ipcperms(&msq->q_perm, S_IWUGO))
			goto out_unlock_free;

		err = security_msg_queue_msgsnd(msq, msg, msgflg);
		if (err)
			goto out_unlock_free;

		if (msgsz + msq->q_cbytes <= msq->q_qbytes &&
				1 + msq->q_qnum <= msq->q_qbytes) {
			break;
		}

		/* queue full, wait: */
		if (msgflg & IPC_NOWAIT) {
			err = -EAGAIN;
			goto out_unlock_free;
		}
		ss_add(msq, &s);
		ipc_rcu_getref(msq);
		msg_unlock(msq);
		schedule();

		ipc_lock_by_ptr(&msq->q_perm);
		ipc_rcu_putref(msq);
		if (msq->q_perm.deleted) {
			err = -EIDRM;
			goto out_unlock_free;
		}
		ss_del(&s);

		if (signal_pending(current)) {
			err = -ERESTARTNOHAND;
			goto out_unlock_free;
		}
	}

	msq->q_lspid = current->tgid;
	msq->q_stime = get_seconds();

	if (!pipelined_send(msq, msg)) {
		/* noone is waiting for this message, enqueue it */
		list_add_tail(&msg->m_list, &msq->q_messages);
		msq->q_cbytes += msgsz;
		msq->q_qnum++;
		atomic_add(msgsz, &msg_bytes);
		atomic_inc(&msg_hdrs);
	}

	err = 0;
	msg = NULL;

out_unlock_free:
	msg_unlock(msq);
out_free:
	if (msg != NULL)
		free_msg(msg);
	return err;
}

static inline int convert_mode(long *msgtyp, int msgflg)
{
	/*
	 *  find message of correct type.
	 *  msgtyp = 0 => get first.
	 *  msgtyp > 0 => get first message of matching type.
	 *  msgtyp < 0 => get message with least type must be < abs(msgtype).
	 */
	if (*msgtyp == 0)
		return SEARCH_ANY;
	if (*msgtyp < 0) {
		*msgtyp = -*msgtyp;
		return SEARCH_LESSEQUAL;
	}
	if (msgflg & MSG_EXCEPT)
		return SEARCH_NOTEQUAL;
	return SEARCH_EQUAL;
}

asmlinkage long sys_msgrcv(int msqid, struct msgbuf __user *msgp, size_t msgsz,
			   long msgtyp, int msgflg)
{
	struct msg_queue *msq;
	struct msg_msg *msg;
	int mode;

	if (msqid < 0 || (long) msgsz < 0)
		return -EINVAL;
	mode = convert_mode(&msgtyp, msgflg);

	msq = msg_lock(msqid);
	if (msq == NULL)
		return -EINVAL;

	msg = ERR_PTR(-EIDRM);
	if (msg_checkid(msq, msqid))
		goto out_unlock;

	for (;;) {
		struct msg_receiver msr_d;
		struct list_head *tmp;

		msg = ERR_PTR(-EACCES);
		if (ipcperms(&msq->q_perm, S_IRUGO))
			goto out_unlock;

		msg = ERR_PTR(-EAGAIN);
		tmp = msq->q_messages.next;
		while (tmp != &msq->q_messages) {
			struct msg_msg *walk_msg;

			walk_msg = list_entry(tmp, struct msg_msg, m_list);
			if (testmsg(walk_msg, msgtyp, mode) &&
			    !security_msg_queue_msgrcv(msq, walk_msg, current,
						       msgtyp, mode)) {

				msg = walk_msg;
				if (mode == SEARCH_LESSEQUAL &&
						walk_msg->m_type != 1) {
					msg = walk_msg;
					msgtyp = walk_msg->m_type - 1;
				} else {
					msg = walk_msg;
					break;
				}
			}
			tmp = tmp->next;
		}
		if (!IS_ERR(msg)) {
			/*
			 * Found a suitable message.
			 * Unlink it from the queue.
			 */
			if ((msgsz < msg->m_ts) && !(msgflg & MSG_NOERROR)) {
				msg = ERR_PTR(-E2BIG);
				goto out_unlock;
			}
			list_del(&msg->m_list);
			msq->q_qnum--;
			msq->q_rtime = get_seconds();
			msq->q_lrpid = current->tgid;
			msq->q_cbytes -= msg->m_ts;
			atomic_sub(msg->m_ts, &msg_bytes);
			atomic_dec(&msg_hdrs);
			ss_wakeup(&msq->q_senders, 0);
			msg_unlock(msq);
			break;
		}
		/* No message waiting. Wait for a message */
		if (msgflg & IPC_NOWAIT) {
			msg = ERR_PTR(-ENOMSG);
			goto out_unlock;
		}
		list_add_tail(&msr_d.r_list, &msq->q_receivers);
		msr_d.r_tsk = current;
		msr_d.r_msgtype = msgtyp;
		msr_d.r_mode = mode;
		if (msgflg & MSG_NOERROR)
			msr_d.r_maxsize = INT_MAX;
		else
			msr_d.r_maxsize = msgsz;
		msr_d.r_msg = ERR_PTR(-EAGAIN);
		current->state = TASK_INTERRUPTIBLE;
		msg_unlock(msq);

		schedule();

		/* Lockless receive, part 1:
		 * Disable preemption.  We don't hold a reference to the queue
		 * and getting a reference would defeat the idea of a lockless
		 * operation, thus the code relies on rcu to guarantee the
		 * existance of msq:
		 * Prior to destruction, expunge_all(-EIRDM) changes r_msg.
		 * Thus if r_msg is -EAGAIN, then the queue not yet destroyed.
		 * rcu_read_lock() prevents preemption between reading r_msg
		 * and the spin_lock() inside ipc_lock_by_ptr().
		 */
		rcu_read_lock();

		/* Lockless receive, part 2:
		 * Wait until pipelined_send or expunge_all are outside of
		 * wake_up_process(). There is a race with exit(), see
		 * ipc/mqueue.c for the details.
		 */
		msg = (struct msg_msg*)msr_d.r_msg;
		while (msg == NULL) {
			cpu_relax();
			msg = (struct msg_msg *)msr_d.r_msg;
		}

		/* Lockless receive, part 3:
		 * If there is a message or an error then accept it without
		 * locking.
		 */
		if (msg != ERR_PTR(-EAGAIN)) {
			rcu_read_unlock();
			break;
		}

		/* Lockless receive, part 3:
		 * Acquire the queue spinlock.
		 */
		ipc_lock_by_ptr(&msq->q_perm);
		rcu_read_unlock();

		/* Lockless receive, part 4:
		 * Repeat test after acquiring the spinlock.
		 */
		msg = (struct msg_msg*)msr_d.r_msg;
		if (msg != ERR_PTR(-EAGAIN))
			goto out_unlock;

		list_del(&msr_d.r_list);
		if (signal_pending(current)) {
			msg = ERR_PTR(-ERESTARTNOHAND);
out_unlock:
			msg_unlock(msq);
			break;
		}
	}
	if (IS_ERR(msg))
		return PTR_ERR(msg);

	msgsz = (msgsz > msg->m_ts) ? msg->m_ts : msgsz;
	if (put_user (msg->m_type, &msgp->mtype) ||
	    store_msg(msgp->mtext, msg, msgsz)) {
		msgsz = -EFAULT;
	}
	free_msg(msg);

	return msgsz;
}

#ifdef CONFIG_PROC_FS
static int sysvipc_msg_proc_show(struct seq_file *s, void *it)
{
	struct msg_queue *msq = it;

	return seq_printf(s,
			"%10d %10d  %4o  %10lu %10lu %5u %5u %5u %5u %5u %5u %10lu %10lu %10lu\n",
			msq->q_perm.key,
			msq->q_id,
			msq->q_perm.mode,
			msq->q_cbytes,
			msq->q_qnum,
			msq->q_lspid,
			msq->q_lrpid,
			msq->q_perm.uid,
			msq->q_perm.gid,
			msq->q_perm.cuid,
			msq->q_perm.cgid,
			msq->q_stime,
			msq->q_rtime,
			msq->q_ctime);
}
#endif