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
  18 #include <linux/capability.h>
  19 #include <linux/config.h>
  20 #include <linux/slab.h>
  21 #include <linux/msg.h>
  22 #include <linux/spinlock.h>
  23 #include <linux/init.h>
  24 #include <linux/proc_fs.h>
  25 #include <linux/list.h>
  26 #include <linux/security.h>
  27 #include <linux/sched.h>
  28 #include <linux/syscalls.h>
  29 #include <linux/audit.h>
  30 #include <linux/seq_file.h>
  31 #include <linux/mutex.h>
  32
  33 #include <asm/current.h>
  34 #include <asm/uaccess.h>
  35 #include "util.h"
  36
  37 /* sysctl: */
  38 int msg_ctlmax = MSGMAX;
  39 int msg_ctlmnb = MSGMNB;
  40 int msg_ctlmni = MSGMNI;
  41
  42 /* one msg_receiver structure for each sleeping receiver */
  43 struct msg_receiver {
  44         struct list_head r_list;
  45         struct task_struct* r_tsk;
  46
  47         int r_mode;
  48         long r_msgtype;
  49         long r_maxsize;
  50
  51         struct msg_msg* volatile r_msg;
  52 };
  53
  54 /* one msg_sender for each sleeping sender */
  55 struct msg_sender {
  56         struct list_head list;
  57         struct task_struct* tsk;
  58 };
  59
  60 #define SEARCH_ANY              1
  61 #define SEARCH_EQUAL            2
  62 #define SEARCH_NOTEQUAL         3
  63 #define SEARCH_LESSEQUAL        4
  64
  65 static atomic_t msg_bytes = ATOMIC_INIT(0);
  66 static atomic_t msg_hdrs = ATOMIC_INIT(0);
  67
  68 static struct ipc_ids msg_ids;
  69
  70 #define msg_lock(id)    ((struct msg_queue*)ipc_lock(&msg_ids,id))
  71 #define msg_unlock(msq) ipc_unlock(&(msq)->q_perm)
  72 #define msg_rmid(id)    ((struct msg_queue*)ipc_rmid(&msg_ids,id))
  73 #define msg_checkid(msq, msgid) \
  74         ipc_checkid(&msg_ids,&msq->q_perm,msgid)
  75 #define msg_buildid(id, seq) \
  76         ipc_buildid(&msg_ids, id, seq)
  77
  78 static void freeque (struct msg_queue *msq, int id);
  79 static int newque (key_t key, int msgflg);
  80 #ifdef CONFIG_PROC_FS
  81 static int sysvipc_msg_proc_show(struct seq_file *s, void *it);
  82 #endif
  83
  84 void __init msg_init (void)
  85 {
  86         ipc_init_ids(&msg_ids,msg_ctlmni);
  87         ipc_init_proc_interface("sysvipc/msg",
  88                                 "       key      msqid perms      cbytes       qnum lspid lrpid   uid   gid  cuid  cgid      stime      rtime      ctime\n",
  89                                 &msg_ids,
  90                                 sysvipc_msg_proc_show);
  91 }
  92
  93 static int newque (key_t key, int msgflg)
  94 {
  95         int id;
  96         int retval;
  97         struct msg_queue *msq;
  98
  99         msq  = ipc_rcu_alloc(sizeof(*msq));
 100         if (!msq)
 101                 return -ENOMEM;
 102
 103         msq->q_perm.mode = (msgflg & S_IRWXUGO);
 104         msq->q_perm.key = key;
 105
 106         msq->q_perm.security = NULL;
 107         retval = security_msg_queue_alloc(msq);
 108         if (retval) {
 109                 ipc_rcu_putref(msq);
 110                 return retval;
 111         }
 112
 113         id = ipc_addid(&msg_ids, &msq->q_perm, msg_ctlmni);
 114         if(id == -1) {
 115                 security_msg_queue_free(msq);
 116                 ipc_rcu_putref(msq);
 117                 return -ENOSPC;
 118         }
 119
 120         msq->q_id = msg_buildid(id,msq->q_perm.seq);
 121         msq->q_stime = msq->q_rtime = 0;
 122         msq->q_ctime = get_seconds();
 123         msq->q_cbytes = msq->q_qnum = 0;
 124         msq->q_qbytes = msg_ctlmnb;
 125         msq->q_lspid = msq->q_lrpid = 0;
 126         INIT_LIST_HEAD(&msq->q_messages);
 127         INIT_LIST_HEAD(&msq->q_receivers);
 128         INIT_LIST_HEAD(&msq->q_senders);
 129         msg_unlock(msq);
 130
 131         return msq->q_id;
 132 }
 133
 134 static inline void ss_add(struct msg_queue* msq, struct msg_sender* mss)
 135 {
 136         mss->tsk=current;
 137         current->state=TASK_INTERRUPTIBLE;
 138         list_add_tail(&mss->list,&msq->q_senders);
 139 }
 140
 141 static inline void ss_del(struct msg_sender* mss)
 142 {
 143         if(mss->list.next != NULL)
 144                 list_del(&mss->list);
 145 }
 146
 147 static void ss_wakeup(struct list_head* h, int kill)
 148 {
 149         struct list_head *tmp;
 150
 151         tmp = h->next;
 152         while (tmp != h) {
 153                 struct msg_sender* mss;
 154
 155                 mss = list_entry(tmp,struct msg_sender,list);
 156                 tmp = tmp->next;
 157                 if(kill)
 158                         mss->list.next=NULL;
 159                 wake_up_process(mss->tsk);
 160         }
 161 }
 162
 163 static void expunge_all(struct msg_queue* msq, int res)
 164 {
 165         struct list_head *tmp;
 166
 167         tmp = msq->q_receivers.next;
 168         while (tmp != &msq->q_receivers) {
 169                 struct msg_receiver* msr;
 170
 171                 msr = list_entry(tmp,struct msg_receiver,r_list);
 172                 tmp = tmp->next;
 173                 msr->r_msg = NULL;
 174                 wake_up_process(msr->r_tsk);
 175                 smp_mb();
 176                 msr->r_msg = ERR_PTR(res);
 177         }
 178 }
 179 /*
 180  * freeque() wakes up waiters on the sender and receiver waiting queue,
 181  * removes the message queue from message queue ID
 182  * array, and cleans up all the messages associated with this queue.
 183  *
 184  * msg_ids.mutex and the spinlock for this message queue is hold
 185  * before freeque() is called. msg_ids.mutex remains locked on exit.
 186  */
 187 static void freeque (struct msg_queue *msq, int id)
 188 {
 189         struct list_head *tmp;
 190
 191         expunge_all(msq,-EIDRM);
 192         ss_wakeup(&msq->q_senders,1);
 193         msq = msg_rmid(id);
 194         msg_unlock(msq);
 195
 196         tmp = msq->q_messages.next;
 197         while(tmp != &msq->q_messages) {
 198                 struct msg_msg* msg = list_entry(tmp,struct msg_msg,m_list);
 199                 tmp = tmp->next;
 200                 atomic_dec(&msg_hdrs);
 201                 free_msg(msg);
 202         }
 203         atomic_sub(msq->q_cbytes, &msg_bytes);
 204         security_msg_queue_free(msq);
 205         ipc_rcu_putref(msq);
 206 }
 207
 208 asmlinkage long sys_msgget (key_t key, int msgflg)
 209 {
 210         int id, ret = -EPERM;
 211         struct msg_queue *msq;
 212
 213         mutex_lock(&msg_ids.mutex);
 214         if (key == IPC_PRIVATE)
 215                 ret = newque(key, msgflg);
 216         else if ((id = ipc_findkey(&msg_ids, key)) == -1) { /* key not used */
 217                 if (!(msgflg & IPC_CREAT))
 218                         ret = -ENOENT;
 219                 else
 220                         ret = newque(key, msgflg);
 221         } else if (msgflg & IPC_CREAT && msgflg & IPC_EXCL) {
 222                 ret = -EEXIST;
 223         } else {
 224                 msq = msg_lock(id);
 225                 BUG_ON(msq==NULL);
 226                 if (ipcperms(&msq->q_perm, msgflg))
 227                         ret = -EACCES;
 228                 else {
 229                         int qid = msg_buildid(id, msq->q_perm.seq);
 230                         ret = security_msg_queue_associate(msq, msgflg);
 231                         if (!ret)
 232                                 ret = qid;
 233                 }
 234                 msg_unlock(msq);
 235         }
 236         mutex_unlock(&msg_ids.mutex);
 237         return ret;
 238 }
 239
 240 static inline unsigned long copy_msqid_to_user(void __user *buf, struct msqid64_ds *in, int version)
 241 {
 242         switch(version) {
 243         case IPC_64:
 244                 return copy_to_user (buf, in, sizeof(*in));
 245         case IPC_OLD:
 246             {
 247                 struct msqid_ds out;
 248
 249                 memset(&out,0,sizeof(out));
 250
 251                 ipc64_perm_to_ipc_perm(&in->msg_perm, &out.msg_perm);
 252
 253                 out.msg_stime           = in->msg_stime;
 254                 out.msg_rtime           = in->msg_rtime;
 255                 out.msg_ctime           = in->msg_ctime;
 256
 257                 if(in->msg_cbytes > USHRT_MAX)
 258                         out.msg_cbytes  = USHRT_MAX;
 259                 else
 260                         out.msg_cbytes  = in->msg_cbytes;
 261                 out.msg_lcbytes         = in->msg_cbytes;
 262
 263                 if(in->msg_qnum > USHRT_MAX)
 264                         out.msg_qnum    = USHRT_MAX;
 265                 else
 266                         out.msg_qnum    = in->msg_qnum;
 267
 268                 if(in->msg_qbytes > USHRT_MAX)
 269                         out.msg_qbytes  = USHRT_MAX;
 270                 else
 271                         out.msg_qbytes  = in->msg_qbytes;
 272                 out.msg_lqbytes         = in->msg_qbytes;
 273
 274                 out.msg_lspid           = in->msg_lspid;
 275                 out.msg_lrpid           = in->msg_lrpid;
 276
 277                 return copy_to_user (buf, &out, sizeof(out));
 278             }
 279         default:
 280                 return -EINVAL;
 281         }
 282 }
 283
 284 struct msq_setbuf {
 285         unsigned long   qbytes;
 286         uid_t           uid;
 287         gid_t           gid;
 288         mode_t          mode;
 289 };
 290
 291 static inline unsigned long copy_msqid_from_user(struct msq_setbuf *out, void __user *buf, int version)
 292 {
 293         switch(version) {
 294         case IPC_64:
 295             {
 296                 struct msqid64_ds tbuf;
 297
 298                 if (copy_from_user (&tbuf, buf, sizeof (tbuf)))
 299                         return -EFAULT;
 300
 301                 out->qbytes             = tbuf.msg_qbytes;
 302                 out->uid                = tbuf.msg_perm.uid;
 303                 out->gid                = tbuf.msg_perm.gid;
 304                 out->mode               = tbuf.msg_perm.mode;
 305
 306                 return 0;
 307             }
 308         case IPC_OLD:
 309             {
 310                 struct msqid_ds tbuf_old;
 311
 312                 if (copy_from_user (&tbuf_old, buf, sizeof (tbuf_old)))
 313                         return -EFAULT;
 314
 315                 out->uid                = tbuf_old.msg_perm.uid;
 316                 out->gid                = tbuf_old.msg_perm.gid;
 317                 out->mode               = tbuf_old.msg_perm.mode;
 318
 319                 if(tbuf_old.msg_qbytes == 0)
 320                         out->qbytes     = tbuf_old.msg_lqbytes;
 321                 else
 322                         out->qbytes     = tbuf_old.msg_qbytes;
 323
 324                 return 0;
 325             }
 326         default:
 327                 return -EINVAL;
 328         }
 329 }
 330
 331 asmlinkage long sys_msgctl (int msqid, int cmd, struct msqid_ds __user *buf)
 332 {
 333         int err, version;
 334         struct msg_queue *msq;
 335         struct msq_setbuf setbuf;
 336         struct kern_ipc_perm *ipcp;
 337
 338         if (msqid < 0 || cmd < 0)
 339                 return -EINVAL;
 340
 341         version = ipc_parse_version(&cmd);
 342
 343         switch (cmd) {
 344         case IPC_INFO:
 345         case MSG_INFO:
 346         {
 347                 struct msginfo msginfo;
 348                 int max_id;
 349                 if (!buf)
 350                         return -EFAULT;
 351                 /* We must not return kernel stack data.
 352                  * due to padding, it's not enough
 353                  * to set all member fields.
 354                  */
 355
 356                 err = security_msg_queue_msgctl(NULL, cmd);
 357                 if (err)
 358                         return err;
 359
 360                 memset(&msginfo,0,sizeof(msginfo));
 361                 msginfo.msgmni = msg_ctlmni;
 362                 msginfo.msgmax = msg_ctlmax;
 363                 msginfo.msgmnb = msg_ctlmnb;
 364                 msginfo.msgssz = MSGSSZ;
 365                 msginfo.msgseg = MSGSEG;
 366                 mutex_lock(&msg_ids.mutex);
 367                 if (cmd == MSG_INFO) {
 368                         msginfo.msgpool = msg_ids.in_use;
 369                         msginfo.msgmap = atomic_read(&msg_hdrs);
 370                         msginfo.msgtql = atomic_read(&msg_bytes);
 371                 } else {
 372                         msginfo.msgmap = MSGMAP;
 373                         msginfo.msgpool = MSGPOOL;
 374                         msginfo.msgtql = MSGTQL;
 375                 }
 376                 max_id = msg_ids.max_id;
 377                 mutex_unlock(&msg_ids.mutex);
 378                 if (copy_to_user (buf, &msginfo, sizeof(struct msginfo)))
 379                         return -EFAULT;
 380                 return (max_id < 0) ? 0: max_id;
 381         }
 382         case MSG_STAT:
 383         case IPC_STAT:
 384         {
 385                 struct msqid64_ds tbuf;
 386                 int success_return;
 387                 if (!buf)
 388                         return -EFAULT;
 389                 if(cmd == MSG_STAT && msqid >= msg_ids.entries->size)
 390                         return -EINVAL;
 391
 392                 memset(&tbuf,0,sizeof(tbuf));
 393
 394                 msq = msg_lock(msqid);
 395                 if (msq == NULL)
 396                         return -EINVAL;
 397
 398                 if(cmd == MSG_STAT) {
 399                         success_return = msg_buildid(msqid, msq->q_perm.seq);
 400                 } else {
 401                         err = -EIDRM;
 402                         if (msg_checkid(msq,msqid))
 403                                 goto out_unlock;
 404                         success_return = 0;
 405                 }
 406                 err = -EACCES;
 407                 if (ipcperms (&msq->q_perm, S_IRUGO))
 408                         goto out_unlock;
 409
 410                 err = security_msg_queue_msgctl(msq, cmd);
 411                 if (err)
 412                         goto out_unlock;
 413
 414                 kernel_to_ipc64_perm(&msq->q_perm, &tbuf.msg_perm);
 415                 tbuf.msg_stime  = msq->q_stime;
 416                 tbuf.msg_rtime  = msq->q_rtime;
 417                 tbuf.msg_ctime  = msq->q_ctime;
 418                 tbuf.msg_cbytes = msq->q_cbytes;
 419                 tbuf.msg_qnum   = msq->q_qnum;
 420                 tbuf.msg_qbytes = msq->q_qbytes;
 421                 tbuf.msg_lspid  = msq->q_lspid;
 422                 tbuf.msg_lrpid  = msq->q_lrpid;
 423                 msg_unlock(msq);
 424                 if (copy_msqid_to_user(buf, &tbuf, version))
 425                         return -EFAULT;
 426                 return success_return;
 427         }
 428         case IPC_SET:
 429                 if (!buf)
 430                         return -EFAULT;
 431                 if (copy_msqid_from_user (&setbuf, buf, version))
 432                         return -EFAULT;
 433                 break;
 434         case IPC_RMID:
 435                 break;
 436         default:
 437                 return  -EINVAL;
 438         }
 439
 440         mutex_lock(&msg_ids.mutex);
 441         msq = msg_lock(msqid);
 442         err=-EINVAL;
 443         if (msq == NULL)
 444                 goto out_up;
 445
 446         err = -EIDRM;
 447         if (msg_checkid(msq,msqid))
 448                 goto out_unlock_up;
 449         ipcp = &msq->q_perm;
 450         err = -EPERM;
 451         if (current->euid != ipcp->cuid &&
 452             current->euid != ipcp->uid && !capable(CAP_SYS_ADMIN))
 453             /* We _could_ check for CAP_CHOWN above, but we don't */
 454                 goto out_unlock_up;
 455
 456         err = security_msg_queue_msgctl(msq, cmd);
 457         if (err)
 458                 goto out_unlock_up;
 459
 460         switch (cmd) {
 461         case IPC_SET:
 462         {
 463                 if ((err = audit_ipc_perms(setbuf.qbytes, setbuf.uid, setbuf.gid, setbuf.mode, ipcp)))
 464                         goto out_unlock_up;
 465
 466                 err = -EPERM;
 467                 if (setbuf.qbytes > msg_ctlmnb && !capable(CAP_SYS_RESOURCE))
 468                         goto out_unlock_up;
 469
 470                 msq->q_qbytes = setbuf.qbytes;
 471
 472                 ipcp->uid = setbuf.uid;
 473                 ipcp->gid = setbuf.gid;
 474                 ipcp->mode = (ipcp->mode & ~S_IRWXUGO) |
 475                         (S_IRWXUGO & setbuf.mode);
 476                 msq->q_ctime = get_seconds();
 477                 /* sleeping receivers might be excluded by
 478                  * stricter permissions.
 479                  */
 480                 expunge_all(msq,-EAGAIN);
 481                 /* sleeping senders might be able to send
 482                  * due to a larger queue size.
 483                  */
 484                 ss_wakeup(&msq->q_senders,0);
 485                 msg_unlock(msq);
 486                 break;
 487         }
 488         case IPC_RMID:
 489                 freeque (msq, msqid);
 490                 break;
 491         }
 492         err = 0;
 493 out_up:
 494         mutex_unlock(&msg_ids.mutex);
 495         return err;
 496 out_unlock_up:
 497         msg_unlock(msq);
 498         goto out_up;
 499 out_unlock:
 500         msg_unlock(msq);
 501         return err;
 502 }
 503
 504 static int testmsg(struct msg_msg* msg,long type,int mode)
 505 {
 506         switch(mode)
 507         {
 508                 case SEARCH_ANY:
 509                         return 1;
 510                 case SEARCH_LESSEQUAL:
 511                         if(msg->m_type <=type)
 512                                 return 1;
 513                         break;
 514                 case SEARCH_EQUAL:
 515                         if(msg->m_type == type)
 516                                 return 1;
 517                         break;
 518                 case SEARCH_NOTEQUAL:
 519                         if(msg->m_type != type)
 520                                 return 1;
 521                         break;
 522         }
 523         return 0;
 524 }
 525
 526 static inline int pipelined_send(struct msg_queue* msq, struct msg_msg* msg)
 527 {
 528         struct list_head* tmp;
 529
 530         tmp = msq->q_receivers.next;
 531         while (tmp != &msq->q_receivers) {
 532                 struct msg_receiver* msr;
 533                 msr = list_entry(tmp,struct msg_receiver,r_list);
 534                 tmp = tmp->next;
 535                 if(testmsg(msg,msr->r_msgtype,msr->r_mode) &&
 536                    !security_msg_queue_msgrcv(msq, msg, msr->r_tsk, msr->r_msgtype, msr->r_mode)) {
 537                         list_del(&msr->r_list);
 538                         if(msr->r_maxsize < msg->m_ts) {
 539                                 msr->r_msg = NULL;
 540                                 wake_up_process(msr->r_tsk);
 541                                 smp_mb();
 542                                 msr->r_msg = ERR_PTR(-E2BIG);
 543                         } else {
 544                                 msr->r_msg = NULL;
 545                                 msq->q_lrpid = msr->r_tsk->pid;
 546                                 msq->q_rtime = get_seconds();
 547                                 wake_up_process(msr->r_tsk);
 548                                 smp_mb();
 549                                 msr->r_msg = msg;
 550                                 return 1;
 551                         }
 552                 }
 553         }
 554         return 0;
 555 }
 556
 557 asmlinkage long sys_msgsnd (int msqid, struct msgbuf __user *msgp, size_t msgsz, int msgflg)
 558 {
 559         struct msg_queue *msq;
 560         struct msg_msg *msg;
 561         long mtype;
 562         int err;
 563
 564         if (msgsz > msg_ctlmax || (long) msgsz < 0 || msqid < 0)
 565                 return -EINVAL;
 566         if (get_user(mtype, &msgp->mtype))
 567                 return -EFAULT;
 568         if (mtype < 1)
 569                 return -EINVAL;
 570
 571         msg = load_msg(msgp->mtext, msgsz);
 572         if(IS_ERR(msg))
 573                 return PTR_ERR(msg);
 574
 575         msg->m_type = mtype;
 576         msg->m_ts = msgsz;
 577
 578         msq = msg_lock(msqid);
 579         err=-EINVAL;
 580         if(msq==NULL)
 581                 goto out_free;
 582
 583         err= -EIDRM;
 584         if (msg_checkid(msq,msqid))
 585                 goto out_unlock_free;
 586
 587         for (;;) {
 588                 struct msg_sender s;
 589
 590                 err=-EACCES;
 591                 if (ipcperms(&msq->q_perm, S_IWUGO))
 592                         goto out_unlock_free;
 593
 594                 err = security_msg_queue_msgsnd(msq, msg, msgflg);
 595                 if (err)
 596                         goto out_unlock_free;
 597
 598                 if(msgsz + msq->q_cbytes <= msq->q_qbytes &&
 599                                 1 + msq->q_qnum <= msq->q_qbytes) {
 600                         break;
 601                 }
 602
 603                 /* queue full, wait: */
 604                 if(msgflg&IPC_NOWAIT) {
 605                         err=-EAGAIN;
 606                         goto out_unlock_free;
 607                 }
 608                 ss_add(msq, &s);
 609                 ipc_rcu_getref(msq);
 610                 msg_unlock(msq);
 611                 schedule();
 612
 613                 ipc_lock_by_ptr(&msq->q_perm);
 614                 ipc_rcu_putref(msq);
 615                 if (msq->q_perm.deleted) {
 616                         err = -EIDRM;
 617                         goto out_unlock_free;
 618                 }
 619                 ss_del(&s);
 620
 621                 if (signal_pending(current)) {
 622                         err=-ERESTARTNOHAND;
 623                         goto out_unlock_free;
 624                 }
 625         }
 626
 627         msq->q_lspid = current->tgid;
 628         msq->q_stime = get_seconds();
 629
 630         if(!pipelined_send(msq,msg)) {
 631                 /* noone is waiting for this message, enqueue it */
 632                 list_add_tail(&msg->m_list,&msq->q_messages);
 633                 msq->q_cbytes += msgsz;
 634                 msq->q_qnum++;
 635                 atomic_add(msgsz,&msg_bytes);
 636                 atomic_inc(&msg_hdrs);
 637         }
 638
 639         err = 0;
 640         msg = NULL;
 641
 642 out_unlock_free:
 643         msg_unlock(msq);
 644 out_free:
 645         if(msg!=NULL)
 646                 free_msg(msg);
 647         return err;
 648 }
 649
 650 static inline int convert_mode(long* msgtyp, int msgflg)
 651 {
 652         /*
 653          *  find message of correct type.
 654          *  msgtyp = 0 => get first.
 655          *  msgtyp > 0 => get first message of matching type.
 656          *  msgtyp < 0 => get message with least type must be < abs(msgtype).
 657          */
 658         if(*msgtyp==0)
 659                 return SEARCH_ANY;
 660         if(*msgtyp<0) {
 661                 *msgtyp=-(*msgtyp);
 662                 return SEARCH_LESSEQUAL;
 663         }
 664         if(msgflg & MSG_EXCEPT)
 665                 return SEARCH_NOTEQUAL;
 666         return SEARCH_EQUAL;
 667 }
 668
 669 asmlinkage long sys_msgrcv (int msqid, struct msgbuf __user *msgp, size_t msgsz,
 670                             long msgtyp, int msgflg)
 671 {
 672         struct msg_queue *msq;
 673         struct msg_msg *msg;
 674         int mode;
 675
 676         if (msqid < 0 || (long) msgsz < 0)
 677                 return -EINVAL;
 678         mode = convert_mode(&msgtyp,msgflg);
 679
 680         msq = msg_lock(msqid);
 681         if(msq==NULL)
 682                 return -EINVAL;
 683
 684         msg = ERR_PTR(-EIDRM);
 685         if (msg_checkid(msq,msqid))
 686                 goto out_unlock;
 687
 688         for (;;) {
 689                 struct msg_receiver msr_d;
 690                 struct list_head* tmp;
 691
 692                 msg = ERR_PTR(-EACCES);
 693                 if (ipcperms (&msq->q_perm, S_IRUGO))
 694                         goto out_unlock;
 695
 696                 msg = ERR_PTR(-EAGAIN);
 697                 tmp = msq->q_messages.next;
 698                 while (tmp != &msq->q_messages) {
 699                         struct msg_msg *walk_msg;
 700                         walk_msg = list_entry(tmp,struct msg_msg,m_list);
 701                         if(testmsg(walk_msg,msgtyp,mode) &&
 702                            !security_msg_queue_msgrcv(msq, walk_msg, current, msgtyp, mode)) {
 703                                 msg = walk_msg;
 704                                 if(mode == SEARCH_LESSEQUAL && walk_msg->m_type != 1) {
 705                                         msg=walk_msg;
 706                                         msgtyp=walk_msg->m_type-1;
 707                                 } else {
 708                                         msg=walk_msg;
 709                                         break;
 710                                 }
 711                         }
 712                         tmp = tmp->next;
 713                 }
 714                 if(!IS_ERR(msg)) {
 715                         /* Found a suitable message. Unlink it from the queue. */
 716                         if ((msgsz < msg->m_ts) && !(msgflg & MSG_NOERROR)) {
 717                                 msg = ERR_PTR(-E2BIG);
 718                                 goto out_unlock;
 719                         }
 720                         list_del(&msg->m_list);
 721                         msq->q_qnum--;
 722                         msq->q_rtime = get_seconds();
 723                         msq->q_lrpid = current->tgid;
 724                         msq->q_cbytes -= msg->m_ts;
 725                         atomic_sub(msg->m_ts,&msg_bytes);
 726                         atomic_dec(&msg_hdrs);
 727                         ss_wakeup(&msq->q_senders,0);
 728                         msg_unlock(msq);
 729                         break;
 730                 }
 731                 /* No message waiting. Wait for a message */
 732                 if (msgflg & IPC_NOWAIT) {
 733                         msg = ERR_PTR(-ENOMSG);
 734                         goto out_unlock;
 735                 }
 736                 list_add_tail(&msr_d.r_list,&msq->q_receivers);
 737                 msr_d.r_tsk = current;
 738                 msr_d.r_msgtype = msgtyp;
 739                 msr_d.r_mode = mode;
 740                 if(msgflg & MSG_NOERROR)
 741                         msr_d.r_maxsize = INT_MAX;
 742                  else
 743                         msr_d.r_maxsize = msgsz;
 744                 msr_d.r_msg = ERR_PTR(-EAGAIN);
 745                 current->state = TASK_INTERRUPTIBLE;
 746                 msg_unlock(msq);
 747
 748                 schedule();
 749
 750                 /* Lockless receive, part 1:
 751                  * Disable preemption.  We don't hold a reference to the queue
 752                  * and getting a reference would defeat the idea of a lockless
 753                  * operation, thus the code relies on rcu to guarantee the
 754                  * existance of msq:
 755                  * Prior to destruction, expunge_all(-EIRDM) changes r_msg.
 756                  * Thus if r_msg is -EAGAIN, then the queue not yet destroyed.
 757                  * rcu_read_lock() prevents preemption between reading r_msg
 758                  * and the spin_lock() inside ipc_lock_by_ptr().
 759                  */
 760                 rcu_read_lock();
 761
 762                 /* Lockless receive, part 2:
 763                  * Wait until pipelined_send or expunge_all are outside of
 764                  * wake_up_process(). There is a race with exit(), see
 765                  * ipc/mqueue.c for the details.
 766                  */
 767                 msg = (struct msg_msg*) msr_d.r_msg;
 768                 while (msg == NULL) {
 769                         cpu_relax();
 770                         msg = (struct msg_msg*) msr_d.r_msg;
 771                 }
 772
 773                 /* Lockless receive, part 3:
 774                  * If there is a message or an error then accept it without
 775                  * locking.
 776                  */
 777                 if(msg != ERR_PTR(-EAGAIN)) {
 778                         rcu_read_unlock();
 779                         break;
 780                 }
 781
 782                 /* Lockless receive, part 3:
 783                  * Acquire the queue spinlock.
 784                  */
 785                 ipc_lock_by_ptr(&msq->q_perm);
 786                 rcu_read_unlock();
 787
 788                 /* Lockless receive, part 4:
 789                  * Repeat test after acquiring the spinlock.
 790                  */
 791                 msg = (struct msg_msg*)msr_d.r_msg;
 792                 if(msg != ERR_PTR(-EAGAIN))
 793                         goto out_unlock;
 794
 795                 list_del(&msr_d.r_list);
 796                 if (signal_pending(current)) {
 797                         msg = ERR_PTR(-ERESTARTNOHAND);
 798 out_unlock:
 799                         msg_unlock(msq);
 800                         break;
 801                 }
 802         }
 803         if (IS_ERR(msg))
 804                 return PTR_ERR(msg);
 805
 806         msgsz = (msgsz > msg->m_ts) ? msg->m_ts : msgsz;
 807         if (put_user (msg->m_type, &msgp->mtype) ||
 808             store_msg(msgp->mtext, msg, msgsz)) {
 809                     msgsz = -EFAULT;
 810         }
 811         free_msg(msg);
 812         return msgsz;
 813 }
 814
 815 #ifdef CONFIG_PROC_FS
 816 static int sysvipc_msg_proc_show(struct seq_file *s, void *it)
 817 {
 818         struct msg_queue *msq = it;
 819
 820         return seq_printf(s,
 821                           "%10d %10d  %4o  %10lu %10lu %5u %5u %5u %5u %5u %5u %10lu %10lu %10lu\n",
 822                           msq->q_perm.key,
 823                           msq->q_id,
 824                           msq->q_perm.mode,
 825                           msq->q_cbytes,
 826                           msq->q_qnum,
 827                           msq->q_lspid,
 828                           msq->q_lrpid,
 829                           msq->q_perm.uid,
 830                           msq->q_perm.gid,
 831                           msq->q_perm.cuid,
 832                           msq->q_perm.cgid,
 833                           msq->q_stime,
 834                           msq->q_rtime,
 835                           msq->q_ctime);
 836 }
 837 #endif