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Root/ipc/msg.c

1	/*
2	* linux/ipc/msg.c
3	* Copyright (C) 1992 Krishna Balasubramanian
4	*
5	* Removed all the remaining kerneld mess
6	* Catch the -EFAULT stuff properly
7	* Use GFP_KERNEL for messages as in 1.2
8	* Fixed up the unchecked user space derefs
9	* Copyright (C) 1998 Alan Cox & Andi Kleen
10	*
11	* /proc/sysvipc/msg support (c) 1999 Dragos Acostachioaie <dragos@iname.com>
12	*
13	* mostly rewritten, threaded and wake-one semantics added
14	* MSGMAX limit removed, sysctl's added
15	* (c) 1999 Manfred Spraul <manfred@colorfullife.com>
16	*
17	* support for audit of ipc object properties and permission changes
18	* Dustin Kirkland <dustin.kirkland@us.ibm.com>
19	*
20	* namespaces support
21	* OpenVZ, SWsoft Inc.
22	* Pavel Emelianov <xemul@openvz.org>
23	*/
24
25	#include <linux/capability.h>
26	#include <linux/msg.h>
27	#include <linux/spinlock.h>
28	#include <linux/init.h>
29	#include <linux/mm.h>
30	#include <linux/proc_fs.h>
31	#include <linux/list.h>
32	#include <linux/security.h>
33	#include <linux/sched.h>
34	#include <linux/syscalls.h>
35	#include <linux/audit.h>
36	#include <linux/seq_file.h>
37	#include <linux/rwsem.h>
38	#include <linux/nsproxy.h>
39	#include <linux/ipc_namespace.h>
40
41	#include <asm/current.h>
42	#include <asm/uaccess.h>
43	#include "util.h"
44
45	/*
46	* one msg_receiver structure for each sleeping receiver:
47	*/
48	struct msg_receiver {
49	struct list_head r_list;
50	struct task_struct *r_tsk;
51
52	int r_mode;
53	long r_msgtype;
54	long r_maxsize;
55
56	struct msg_msg *volatile r_msg;
57	};
58
59	/* one msg_sender for each sleeping sender */
60	struct msg_sender {
61	struct list_head list;
62	struct task_struct *tsk;
63	};
64
65	#define SEARCH_ANY 1
66	#define SEARCH_EQUAL 2
67	#define SEARCH_NOTEQUAL 3
68	#define SEARCH_LESSEQUAL 4
69
70	#define msg_ids(ns) ((ns)->ids[IPC_MSG_IDS])
71
72	#define msg_unlock(msq) ipc_unlock(&(msq)->q_perm)
73
74	static void freeque(struct ipc_namespace , struct kern_ipc_perm );
75	static int newque(struct ipc_namespace , struct ipc_params );
76	#ifdef CONFIG_PROC_FS
77	static int sysvipc_msg_proc_show(struct seq_file s, void it);
78	#endif
79
80	/*
81	* Scale msgmni with the available lowmem size: the memory dedicated to msg
82	* queues should occupy at most 1/MSG_MEM_SCALE of lowmem.
83	* Also take into account the number of nsproxies created so far.
84	* This should be done staying within the (MSGMNI , IPCMNI/nr_ipc_ns) range.
85	*/
86	void recompute_msgmni(struct ipc_namespace *ns)
87	{
88	struct sysinfo i;
89	unsigned long allowed;
90	int nb_ns;
91
92	si_meminfo(&i);
93	allowed = (((i.totalram - i.totalhigh) / MSG_MEM_SCALE) * i.mem_unit)
94	/ MSGMNB;
95	nb_ns = atomic_read(&nr_ipc_ns);
96	allowed /= nb_ns;
97
98	if (allowed < MSGMNI) {
99	ns->msg_ctlmni = MSGMNI;
100	return;
101	}
102
103	if (allowed > IPCMNI / nb_ns) {
104	ns->msg_ctlmni = IPCMNI / nb_ns;
105	return;
106	}
107
108	ns->msg_ctlmni = allowed;
109	}
110
111	void msg_init_ns(struct ipc_namespace *ns)
112	{
113	ns->msg_ctlmax = MSGMAX;
114	ns->msg_ctlmnb = MSGMNB;
115
116	recompute_msgmni(ns);
117
118	atomic_set(&ns->msg_bytes, 0);
119	atomic_set(&ns->msg_hdrs, 0);
120	ipc_init_ids(&ns->ids[IPC_MSG_IDS]);
121	}
122
123	#ifdef CONFIG_IPC_NS
124	void msg_exit_ns(struct ipc_namespace *ns)
125	{
126	free_ipcs(ns, &msg_ids(ns), freeque);
127	idr_destroy(&ns->ids[IPC_MSG_IDS].ipcs_idr);
128	}
129	#endif
130
131	void __init msg_init(void)
132	{
133	msg_init_ns(&init_ipc_ns);
134
135	printk(KERN_INFO "msgmni has been set to %d\n",
136	init_ipc_ns.msg_ctlmni);
137
138	ipc_init_proc_interface("sysvipc/msg",
139	" key msqid perms cbytes qnum lspid lrpid uid gid cuid cgid stime rtime ctime\n",
140	IPC_MSG_IDS, sysvipc_msg_proc_show);
141	}
142
143	/*
144	* msg_lock_(check_) routines are called in the paths where the rw_mutex
145	* is not held.
146	*/
147	static inline struct msg_queue msg_lock(struct ipc_namespace ns, int id)
148	{
149	struct kern_ipc_perm *ipcp = ipc_lock(&msg_ids(ns), id);
150
151	if (IS_ERR(ipcp))
152	return (struct msg_queue *)ipcp;
153
154	return container_of(ipcp, struct msg_queue, q_perm);
155	}
156
157	static inline struct msg_queue msg_lock_check(struct ipc_namespace ns,
158	int id)
159	{
160	struct kern_ipc_perm *ipcp = ipc_lock_check(&msg_ids(ns), id);
161
162	if (IS_ERR(ipcp))
163	return (struct msg_queue *)ipcp;
164
165	return container_of(ipcp, struct msg_queue, q_perm);
166	}
167
168	static inline void msg_rmid(struct ipc_namespace ns, struct msg_queue s)
169	{
170	ipc_rmid(&msg_ids(ns), &s->q_perm);
171	}
172
173	/**
174	* newque - Create a new msg queue
175	* @ns: namespace
176	* @params: ptr to the structure that contains the key and msgflg
177	*
178	* Called with msg_ids.rw_mutex held (writer)
179	*/
180	static int newque(struct ipc_namespace ns, struct ipc_params params)
181	{
182	struct msg_queue *msq;
183	int id, retval;
184	key_t key = params->key;
185	int msgflg = params->flg;
186
187	msq = ipc_rcu_alloc(sizeof(*msq));
188	if (!msq)
189	return -ENOMEM;
190
191	msq->q_perm.mode = msgflg & S_IRWXUGO;
192	msq->q_perm.key = key;
193
194	msq->q_perm.security = NULL;
195	retval = security_msg_queue_alloc(msq);
196	if (retval) {
197	ipc_rcu_putref(msq);
198	return retval;
199	}
200
201	/*
202	* ipc_addid() locks msq
203	*/
204	id = ipc_addid(&msg_ids(ns), &msq->q_perm, ns->msg_ctlmni);
205	if (id < 0) {
206	security_msg_queue_free(msq);
207	ipc_rcu_putref(msq);
208	return id;
209	}
210
211	msq->q_stime = msq->q_rtime = 0;
212	msq->q_ctime = get_seconds();
213	msq->q_cbytes = msq->q_qnum = 0;
214	msq->q_qbytes = ns->msg_ctlmnb;
215	msq->q_lspid = msq->q_lrpid = 0;
216	INIT_LIST_HEAD(&msq->q_messages);
217	INIT_LIST_HEAD(&msq->q_receivers);
218	INIT_LIST_HEAD(&msq->q_senders);
219
220	msg_unlock(msq);
221
222	return msq->q_perm.id;
223	}
224
225	static inline void ss_add(struct msg_queue msq, struct msg_sender mss)
226	{
227	mss->tsk = current;
228	current->state = TASK_INTERRUPTIBLE;
229	list_add_tail(&mss->list, &msq->q_senders);
230	}
231
232	static inline void ss_del(struct msg_sender *mss)
233	{
234	if (mss->list.next != NULL)
235	list_del(&mss->list);
236	}
237
238	static void ss_wakeup(struct list_head *h, int kill)
239	{
240	struct list_head *tmp;
241
242	tmp = h->next;
243	while (tmp != h) {
244	struct msg_sender *mss;
245
246	mss = list_entry(tmp, struct msg_sender, list);
247	tmp = tmp->next;
248	if (kill)
249	mss->list.next = NULL;
250	wake_up_process(mss->tsk);
251	}
252	}
253
254	static void expunge_all(struct msg_queue *msq, int res)
255	{
256	struct list_head *tmp;
257
258	tmp = msq->q_receivers.next;
259	while (tmp != &msq->q_receivers) {
260	struct msg_receiver *msr;
261
262	msr = list_entry(tmp, struct msg_receiver, r_list);
263	tmp = tmp->next;
264	msr->r_msg = NULL;
265	wake_up_process(msr->r_tsk);
266	smp_mb();
267	msr->r_msg = ERR_PTR(res);
268	}
269	}
270
271	/*
272	* freeque() wakes up waiters on the sender and receiver waiting queue,
273	* removes the message queue from message queue ID IDR, and cleans up all the
274	* messages associated with this queue.
275	*
276	* msg_ids.rw_mutex (writer) and the spinlock for this message queue are held
277	* before freeque() is called. msg_ids.rw_mutex remains locked on exit.
278	*/
279	static void freeque(struct ipc_namespace ns, struct kern_ipc_perm ipcp)
280	{
281	struct list_head *tmp;
282	struct msg_queue *msq = container_of(ipcp, struct msg_queue, q_perm);
283
284	expunge_all(msq, -EIDRM);
285	ss_wakeup(&msq->q_senders, 1);
286	msg_rmid(ns, msq);
287	msg_unlock(msq);
288
289	tmp = msq->q_messages.next;
290	while (tmp != &msq->q_messages) {
291	struct msg_msg *msg = list_entry(tmp, struct msg_msg, m_list);
292
293	tmp = tmp->next;
294	atomic_dec(&ns->msg_hdrs);
295	free_msg(msg);
296	}
297	atomic_sub(msq->q_cbytes, &ns->msg_bytes);
298	security_msg_queue_free(msq);
299	ipc_rcu_putref(msq);
300	}
301
302	/*
303	* Called with msg_ids.rw_mutex and ipcp locked.
304	*/
305	static inline int msg_security(struct kern_ipc_perm *ipcp, int msgflg)
306	{
307	struct msg_queue *msq = container_of(ipcp, struct msg_queue, q_perm);
308
309	return security_msg_queue_associate(msq, msgflg);
310	}
311
312	SYSCALL_DEFINE2(msgget, key_t, key, int, msgflg)
313	{
314	struct ipc_namespace *ns;
315	struct ipc_ops msg_ops;
316	struct ipc_params msg_params;
317
318	ns = current->nsproxy->ipc_ns;
319
320	msg_ops.getnew = newque;
321	msg_ops.associate = msg_security;
322	msg_ops.more_checks = NULL;
323
324	msg_params.key = key;
325	msg_params.flg = msgflg;
326
327	return ipcget(ns, &msg_ids(ns), &msg_ops, &msg_params);
328	}
329
330	static inline unsigned long
331	copy_msqid_to_user(void __user buf, struct msqid64_ds in, int version)
332	{
333	switch(version) {
334	case IPC_64:
335	return copy_to_user(buf, in, sizeof(*in));
336	case IPC_OLD:
337	{
338	struct msqid_ds out;
339
340	memset(&out, 0, sizeof(out));
341
342	ipc64_perm_to_ipc_perm(&in->msg_perm, &out.msg_perm);
343
344	out.msg_stime = in->msg_stime;
345	out.msg_rtime = in->msg_rtime;
346	out.msg_ctime = in->msg_ctime;
347
348	if (in->msg_cbytes > USHORT_MAX)
349	out.msg_cbytes = USHORT_MAX;
350	else
351	out.msg_cbytes = in->msg_cbytes;
352	out.msg_lcbytes = in->msg_cbytes;
353
354	if (in->msg_qnum > USHORT_MAX)
355	out.msg_qnum = USHORT_MAX;
356	else
357	out.msg_qnum = in->msg_qnum;
358
359	if (in->msg_qbytes > USHORT_MAX)
360	out.msg_qbytes = USHORT_MAX;
361	else
362	out.msg_qbytes = in->msg_qbytes;
363	out.msg_lqbytes = in->msg_qbytes;
364
365	out.msg_lspid = in->msg_lspid;
366	out.msg_lrpid = in->msg_lrpid;
367
368	return copy_to_user(buf, &out, sizeof(out));
369	}
370	default:
371	return -EINVAL;
372	}
373	}
374
375	static inline unsigned long
376	copy_msqid_from_user(struct msqid64_ds out, void __user buf, int version)
377	{
378	switch(version) {
379	case IPC_64:
380	if (copy_from_user(out, buf, sizeof(*out)))
381	return -EFAULT;
382	return 0;
383	case IPC_OLD:
384	{
385	struct msqid_ds tbuf_old;
386
387	if (copy_from_user(&tbuf_old, buf, sizeof(tbuf_old)))
388	return -EFAULT;
389
390	out->msg_perm.uid = tbuf_old.msg_perm.uid;
391	out->msg_perm.gid = tbuf_old.msg_perm.gid;
392	out->msg_perm.mode = tbuf_old.msg_perm.mode;
393
394	if (tbuf_old.msg_qbytes == 0)
395	out->msg_qbytes = tbuf_old.msg_lqbytes;
396	else
397	out->msg_qbytes = tbuf_old.msg_qbytes;
398
399	return 0;
400	}
401	default:
402	return -EINVAL;
403	}
404	}
405
406	/*
407	* This function handles some msgctl commands which require the rw_mutex
408	* to be held in write mode.
409	* NOTE: no locks must be held, the rw_mutex is taken inside this function.
410	*/
411	static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
412	struct msqid_ds __user *buf, int version)
413	{
414	struct kern_ipc_perm *ipcp;
415	struct msqid64_ds uninitialized_var(msqid64);
416	struct msg_queue *msq;
417	int err;
418
419	if (cmd == IPC_SET) {
420	if (copy_msqid_from_user(&msqid64, buf, version))
421	return -EFAULT;
422	}
423
424	ipcp = ipcctl_pre_down(&msg_ids(ns), msqid, cmd,
425	&msqid64.msg_perm, msqid64.msg_qbytes);
426	if (IS_ERR(ipcp))
427	return PTR_ERR(ipcp);
428
429	msq = container_of(ipcp, struct msg_queue, q_perm);
430
431	err = security_msg_queue_msgctl(msq, cmd);
432	if (err)
433	goto out_unlock;
434
435	switch (cmd) {
436	case IPC_RMID:
437	freeque(ns, ipcp);
438	goto out_up;
439	case IPC_SET:
440	if (msqid64.msg_qbytes > ns->msg_ctlmnb &&
441	!capable(CAP_SYS_RESOURCE)) {
442	err = -EPERM;
443	goto out_unlock;
444	}
445
446	msq->q_qbytes = msqid64.msg_qbytes;
447
448	ipc_update_perm(&msqid64.msg_perm, ipcp);
449	msq->q_ctime = get_seconds();
450	/* sleeping receivers might be excluded by
451	* stricter permissions.
452	*/
453	expunge_all(msq, -EAGAIN);
454	/* sleeping senders might be able to send
455	* due to a larger queue size.
456	*/
457	ss_wakeup(&msq->q_senders, 0);
458	break;
459	default:
460	err = -EINVAL;
461	}
462	out_unlock:
463	msg_unlock(msq);
464	out_up:
465	up_write(&msg_ids(ns).rw_mutex);
466	return err;
467	}
468
469	SYSCALL_DEFINE3(msgctl, int, msqid, int, cmd, struct msqid_ds __user *, buf)
470	{
471	struct msg_queue *msq;
472	int err, version;
473	struct ipc_namespace *ns;
474
475	if (msqid < 0 \|\| cmd < 0)
476	return -EINVAL;
477
478	version = ipc_parse_version(&cmd);
479	ns = current->nsproxy->ipc_ns;
480
481	switch (cmd) {
482	case IPC_INFO:
483	case MSG_INFO:
484	{
485	struct msginfo msginfo;
486	int max_id;
487
488	if (!buf)
489	return -EFAULT;
490	/*
491	* We must not return kernel stack data.
492	* due to padding, it's not enough
493	* to set all member fields.
494	*/
495	err = security_msg_queue_msgctl(NULL, cmd);
496	if (err)
497	return err;
498
499	memset(&msginfo, 0, sizeof(msginfo));
500	msginfo.msgmni = ns->msg_ctlmni;
501	msginfo.msgmax = ns->msg_ctlmax;
502	msginfo.msgmnb = ns->msg_ctlmnb;
503	msginfo.msgssz = MSGSSZ;
504	msginfo.msgseg = MSGSEG;
505	down_read(&msg_ids(ns).rw_mutex);
506	if (cmd == MSG_INFO) {
507	msginfo.msgpool = msg_ids(ns).in_use;
508	msginfo.msgmap = atomic_read(&ns->msg_hdrs);
509	msginfo.msgtql = atomic_read(&ns->msg_bytes);
510	} else {
511	msginfo.msgmap = MSGMAP;
512	msginfo.msgpool = MSGPOOL;
513	msginfo.msgtql = MSGTQL;
514	}
515	max_id = ipc_get_maxid(&msg_ids(ns));
516	up_read(&msg_ids(ns).rw_mutex);
517	if (copy_to_user(buf, &msginfo, sizeof(struct msginfo)))
518	return -EFAULT;
519	return (max_id < 0) ? 0 : max_id;
520	}
521	case MSG_STAT: /* msqid is an index rather than a msg queue id */
522	case IPC_STAT:
523	{
524	struct msqid64_ds tbuf;
525	int success_return;
526
527	if (!buf)
528	return -EFAULT;
529
530	if (cmd == MSG_STAT) {
531	msq = msg_lock(ns, msqid);
532	if (IS_ERR(msq))
533	return PTR_ERR(msq);
534	success_return = msq->q_perm.id;
535	} else {
536	msq = msg_lock_check(ns, msqid);
537	if (IS_ERR(msq))
538	return PTR_ERR(msq);
539	success_return = 0;
540	}
541	err = -EACCES;
542	if (ipcperms(&msq->q_perm, S_IRUGO))
543	goto out_unlock;
544
545	err = security_msg_queue_msgctl(msq, cmd);
546	if (err)
547	goto out_unlock;
548
549	memset(&tbuf, 0, sizeof(tbuf));
550
551	kernel_to_ipc64_perm(&msq->q_perm, &tbuf.msg_perm);
552	tbuf.msg_stime = msq->q_stime;
553	tbuf.msg_rtime = msq->q_rtime;
554	tbuf.msg_ctime = msq->q_ctime;
555	tbuf.msg_cbytes = msq->q_cbytes;
556	tbuf.msg_qnum = msq->q_qnum;
557	tbuf.msg_qbytes = msq->q_qbytes;
558	tbuf.msg_lspid = msq->q_lspid;
559	tbuf.msg_lrpid = msq->q_lrpid;
560	msg_unlock(msq);
561	if (copy_msqid_to_user(buf, &tbuf, version))
562	return -EFAULT;
563	return success_return;
564	}
565	case IPC_SET:
566	case IPC_RMID:
567	err = msgctl_down(ns, msqid, cmd, buf, version);
568	return err;
569	default:
570	return -EINVAL;
571	}
572
573	out_unlock:
574	msg_unlock(msq);
575	return err;
576	}
577
578	static int testmsg(struct msg_msg *msg, long type, int mode)
579	{
580	switch(mode)
581	{
582	case SEARCH_ANY:
583	return 1;
584	case SEARCH_LESSEQUAL:
585	if (msg->m_type <=type)
586	return 1;
587	break;
588	case SEARCH_EQUAL:
589	if (msg->m_type == type)
590	return 1;
591	break;
592	case SEARCH_NOTEQUAL:
593	if (msg->m_type != type)
594	return 1;
595	break;
596	}
597	return 0;
598	}
599
600	static inline int pipelined_send(struct msg_queue msq, struct msg_msg msg)
601	{
602	struct list_head *tmp;
603
604	tmp = msq->q_receivers.next;
605	while (tmp != &msq->q_receivers) {
606	struct msg_receiver *msr;
607
608	msr = list_entry(tmp, struct msg_receiver, r_list);
609	tmp = tmp->next;
610	if (testmsg(msg, msr->r_msgtype, msr->r_mode) &&
611	!security_msg_queue_msgrcv(msq, msg, msr->r_tsk,
612	msr->r_msgtype, msr->r_mode)) {
613
614	list_del(&msr->r_list);
615	if (msr->r_maxsize < msg->m_ts) {
616	msr->r_msg = NULL;
617	wake_up_process(msr->r_tsk);
618	smp_mb();
619	msr->r_msg = ERR_PTR(-E2BIG);
620	} else {
621	msr->r_msg = NULL;
622	msq->q_lrpid = task_pid_vnr(msr->r_tsk);
623	msq->q_rtime = get_seconds();
624	wake_up_process(msr->r_tsk);
625	smp_mb();
626	msr->r_msg = msg;
627
628	return 1;
629	}
630	}
631	}
632	return 0;
633	}
634
635	long do_msgsnd(int msqid, long mtype, void __user *mtext,
636	size_t msgsz, int msgflg)
637	{
638	struct msg_queue *msq;
639	struct msg_msg *msg;
640	int err;
641	struct ipc_namespace *ns;
642
643	ns = current->nsproxy->ipc_ns;
644
645	if (msgsz > ns->msg_ctlmax \|\| (long) msgsz < 0 \|\| msqid < 0)
646	return -EINVAL;
647	if (mtype < 1)
648	return -EINVAL;
649
650	msg = load_msg(mtext, msgsz);
651	if (IS_ERR(msg))
652	return PTR_ERR(msg);
653
654	msg->m_type = mtype;
655	msg->m_ts = msgsz;
656
657	msq = msg_lock_check(ns, msqid);
658	if (IS_ERR(msq)) {
659	err = PTR_ERR(msq);
660	goto out_free;
661	}
662
663	for (;;) {
664	struct msg_sender s;
665
666	err = -EACCES;
667	if (ipcperms(&msq->q_perm, S_IWUGO))
668	goto out_unlock_free;
669
670	err = security_msg_queue_msgsnd(msq, msg, msgflg);
671	if (err)
672	goto out_unlock_free;
673
674	if (msgsz + msq->q_cbytes <= msq->q_qbytes &&
675	1 + msq->q_qnum <= msq->q_qbytes) {
676	break;
677	}
678
679	/* queue full, wait: */
680	if (msgflg & IPC_NOWAIT) {
681	err = -EAGAIN;
682	goto out_unlock_free;
683	}
684	ss_add(msq, &s);
685	ipc_rcu_getref(msq);
686	msg_unlock(msq);
687	schedule();
688
689	ipc_lock_by_ptr(&msq->q_perm);
690	ipc_rcu_putref(msq);
691	if (msq->q_perm.deleted) {
692	err = -EIDRM;
693	goto out_unlock_free;
694	}
695	ss_del(&s);
696
697	if (signal_pending(current)) {
698	err = -ERESTARTNOHAND;
699	goto out_unlock_free;
700	}
701	}
702
703	msq->q_lspid = task_tgid_vnr(current);
704	msq->q_stime = get_seconds();
705
706	if (!pipelined_send(msq, msg)) {
707	/* noone is waiting for this message, enqueue it */
708	list_add_tail(&msg->m_list, &msq->q_messages);
709	msq->q_cbytes += msgsz;
710	msq->q_qnum++;
711	atomic_add(msgsz, &ns->msg_bytes);
712	atomic_inc(&ns->msg_hdrs);
713	}
714
715	err = 0;
716	msg = NULL;
717
718	out_unlock_free:
719	msg_unlock(msq);
720	out_free:
721	if (msg != NULL)
722	free_msg(msg);
723	return err;
724	}
725
726	SYSCALL_DEFINE4(msgsnd, int, msqid, struct msgbuf __user *, msgp, size_t, msgsz,
727	int, msgflg)
728	{
729	long mtype;
730
731	if (get_user(mtype, &msgp->mtype))
732	return -EFAULT;
733	return do_msgsnd(msqid, mtype, msgp->mtext, msgsz, msgflg);
734	}
735
736	static inline int convert_mode(long *msgtyp, int msgflg)
737	{
738	/*
739	* find message of correct type.
740	* msgtyp = 0 => get first.
741	* msgtyp > 0 => get first message of matching type.
742	* msgtyp < 0 => get message with least type must be < abs(msgtype).
743	*/
744	if (*msgtyp == 0)
745	return SEARCH_ANY;
746	if (*msgtyp < 0) {
747	msgtyp = -msgtyp;
748	return SEARCH_LESSEQUAL;
749	}
750	if (msgflg & MSG_EXCEPT)
751	return SEARCH_NOTEQUAL;
752	return SEARCH_EQUAL;
753	}
754
755	long do_msgrcv(int msqid, long pmtype, void __user mtext,
756	size_t msgsz, long msgtyp, int msgflg)
757	{
758	struct msg_queue *msq;
759	struct msg_msg *msg;
760	int mode;
761	struct ipc_namespace *ns;
762
763	if (msqid < 0 \|\| (long) msgsz < 0)
764	return -EINVAL;
765	mode = convert_mode(&msgtyp, msgflg);
766	ns = current->nsproxy->ipc_ns;
767
768	msq = msg_lock_check(ns, msqid);
769	if (IS_ERR(msq))
770	return PTR_ERR(msq);
771
772	for (;;) {
773	struct msg_receiver msr_d;
774	struct list_head *tmp;
775
776	msg = ERR_PTR(-EACCES);
777	if (ipcperms(&msq->q_perm, S_IRUGO))
778	goto out_unlock;
779
780	msg = ERR_PTR(-EAGAIN);
781	tmp = msq->q_messages.next;
782	while (tmp != &msq->q_messages) {
783	struct msg_msg *walk_msg;
784
785	walk_msg = list_entry(tmp, struct msg_msg, m_list);
786	if (testmsg(walk_msg, msgtyp, mode) &&
787	!security_msg_queue_msgrcv(msq, walk_msg, current,
788	msgtyp, mode)) {
789
790	msg = walk_msg;
791	if (mode == SEARCH_LESSEQUAL &&
792	walk_msg->m_type != 1) {
793	msg = walk_msg;
794	msgtyp = walk_msg->m_type - 1;
795	} else {
796	msg = walk_msg;
797	break;
798	}
799	}
800	tmp = tmp->next;
801	}
802	if (!IS_ERR(msg)) {
803	/*
804	* Found a suitable message.
805	* Unlink it from the queue.
806	*/
807	if ((msgsz < msg->m_ts) && !(msgflg & MSG_NOERROR)) {
808	msg = ERR_PTR(-E2BIG);
809	goto out_unlock;
810	}
811	list_del(&msg->m_list);
812	msq->q_qnum--;
813	msq->q_rtime = get_seconds();
814	msq->q_lrpid = task_tgid_vnr(current);
815	msq->q_cbytes -= msg->m_ts;
816	atomic_sub(msg->m_ts, &ns->msg_bytes);
817	atomic_dec(&ns->msg_hdrs);
818	ss_wakeup(&msq->q_senders, 0);
819	msg_unlock(msq);
820	break;
821	}
822	/* No message waiting. Wait for a message */
823	if (msgflg & IPC_NOWAIT) {
824	msg = ERR_PTR(-ENOMSG);
825	goto out_unlock;
826	}
827	list_add_tail(&msr_d.r_list, &msq->q_receivers);
828	msr_d.r_tsk = current;
829	msr_d.r_msgtype = msgtyp;
830	msr_d.r_mode = mode;
831	if (msgflg & MSG_NOERROR)
832	msr_d.r_maxsize = INT_MAX;
833	else
834	msr_d.r_maxsize = msgsz;
835	msr_d.r_msg = ERR_PTR(-EAGAIN);
836	current->state = TASK_INTERRUPTIBLE;
837	msg_unlock(msq);
838
839	schedule();
840
841	/* Lockless receive, part 1:
842	* Disable preemption. We don't hold a reference to the queue
843	* and getting a reference would defeat the idea of a lockless
844	* operation, thus the code relies on rcu to guarantee the
845	* existance of msq:
846	* Prior to destruction, expunge_all(-EIRDM) changes r_msg.
847	* Thus if r_msg is -EAGAIN, then the queue not yet destroyed.
848	* rcu_read_lock() prevents preemption between reading r_msg
849	* and the spin_lock() inside ipc_lock_by_ptr().
850	*/
851	rcu_read_lock();
852
853	/* Lockless receive, part 2:
854	* Wait until pipelined_send or expunge_all are outside of
855	* wake_up_process(). There is a race with exit(), see
856	* ipc/mqueue.c for the details.
857	*/
858	msg = (struct msg_msg*)msr_d.r_msg;
859	while (msg == NULL) {
860	cpu_relax();
861	msg = (struct msg_msg *)msr_d.r_msg;
862	}
863
864	/* Lockless receive, part 3:
865	* If there is a message or an error then accept it without
866	* locking.
867	*/
868	if (msg != ERR_PTR(-EAGAIN)) {
869	rcu_read_unlock();
870	break;
871	}
872
873	/* Lockless receive, part 3:
874	* Acquire the queue spinlock.
875	*/
876	ipc_lock_by_ptr(&msq->q_perm);
877	rcu_read_unlock();
878
879	/* Lockless receive, part 4:
880	* Repeat test after acquiring the spinlock.
881	*/
882	msg = (struct msg_msg*)msr_d.r_msg;
883	if (msg != ERR_PTR(-EAGAIN))
884	goto out_unlock;
885
886	list_del(&msr_d.r_list);
887	if (signal_pending(current)) {
888	msg = ERR_PTR(-ERESTARTNOHAND);
889	out_unlock:
890	msg_unlock(msq);
891	break;
892	}
893	}
894	if (IS_ERR(msg))
895	return PTR_ERR(msg);
896
897	msgsz = (msgsz > msg->m_ts) ? msg->m_ts : msgsz;
898	*pmtype = msg->m_type;
899	if (store_msg(mtext, msg, msgsz))
900	msgsz = -EFAULT;
901
902	free_msg(msg);
903
904	return msgsz;
905	}
906
907	SYSCALL_DEFINE5(msgrcv, int, msqid, struct msgbuf __user *, msgp, size_t, msgsz,
908	long, msgtyp, int, msgflg)
909	{
910	long err, mtype;
911
912	err = do_msgrcv(msqid, &mtype, msgp->mtext, msgsz, msgtyp, msgflg);
913	if (err < 0)
914	goto out;
915
916	if (put_user(mtype, &msgp->mtype))
917	err = -EFAULT;
918	out:
919	return err;
920	}
921
922	#ifdef CONFIG_PROC_FS
923	static int sysvipc_msg_proc_show(struct seq_file s, void it)
924	{
925	struct msg_queue *msq = it;
926
927	return seq_printf(s,
928	"%10d %10d %4o %10lu %10lu %5u %5u %5u %5u %5u %5u %10lu %10lu %10lu\n",
929	msq->q_perm.key,
930	msq->q_perm.id,
931	msq->q_perm.mode,
932	msq->q_cbytes,
933	msq->q_qnum,
934	msq->q_lspid,
935	msq->q_lrpid,
936	msq->q_perm.uid,
937	msq->q_perm.gid,
938	msq->q_perm.cuid,
939	msq->q_perm.cgid,
940	msq->q_stime,
941	msq->q_rtime,
942	msq->q_ctime);
943	}
944	#endif
945

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