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 <manfreds@colorfullife.com>
  16  */
  17
  18 #include <linux/config.h>
  19 #include <linux/slab.h>
  20 #include <linux/msg.h>
  21 #include <linux/spinlock.h>
  22 #include <linux/init.h>
  23 #include <linux/proc_fs.h>
  24 #include <linux/list.h>
  25 #include <linux/security.h>
  26 #include <linux/sched.h>
  27 #include <asm/current.h>
  28 #include <asm/uaccess.h>
  29 #include "util.h"
  30
  31 /* sysctl: */
  32 int msg_ctlmax = MSGMAX;
  33 int msg_ctlmnb = MSGMNB;
  34 int msg_ctlmni = MSGMNI;
  35
  36 /* one msg_receiver structure for each sleeping receiver */
  37 struct msg_receiver {
  38         struct list_head r_list;
  39         struct task_struct* r_tsk;
  40
  41         int r_mode;
  42         long r_msgtype;
  43         long r_maxsize;
  44
  45         struct msg_msg* volatile r_msg;
  46 };
  47
  48 /* one msg_sender for each sleeping sender */
  49 struct msg_sender {
  50         struct list_head list;
  51         struct task_struct* tsk;
  52 };
  53
  54 #define SEARCH_ANY              1
  55 #define SEARCH_EQUAL            2
  56 #define SEARCH_NOTEQUAL         3
  57 #define SEARCH_LESSEQUAL        4
  58
  59 static atomic_t msg_bytes = ATOMIC_INIT(0);
  60 static atomic_t msg_hdrs = ATOMIC_INIT(0);
  61
  62 static struct ipc_ids msg_ids;
  63
  64 #define msg_lock(id)    ((struct msg_queue*)ipc_lock(&msg_ids,id))
  65 #define msg_unlock(msq) ipc_unlock(&(msq)->q_perm)
  66 #define msg_rmid(id)    ((struct msg_queue*)ipc_rmid(&msg_ids,id))
  67 #define msg_checkid(msq, msgid) \
  68         ipc_checkid(&msg_ids,&msq->q_perm,msgid)
  69 #define msg_buildid(id, seq) \
  70         ipc_buildid(&msg_ids, id, seq)
  71
  72 static void freeque (struct msg_queue *msq, int id);
  73 static int newque (key_t key, int msgflg);
  74 #ifdef CONFIG_PROC_FS
  75 static int sysvipc_msg_read_proc(char *buffer, char **start, off_t offset, int length, int *eof, void *data);
  76 #endif
  77
  78 void __init msg_init (void)
  79 {
  80         ipc_init_ids(&msg_ids,msg_ctlmni);
  81
  82 #ifdef CONFIG_PROC_FS
  83         create_proc_read_entry("sysvipc/msg", 0, NULL, sysvipc_msg_read_proc, NULL);
  84 #endif
  85 }
  86
  87 static int newque (key_t key, int msgflg)
  88 {
  89         int id;
  90         int retval;
  91         struct msg_queue *msq;
  92
  93         msq  = ipc_rcu_alloc(sizeof(*msq));
  94         if (!msq)
  95                 return -ENOMEM;
  96
  97         msq->q_perm.mode = (msgflg & S_IRWXUGO);
  98         msq->q_perm.key = key;
  99
 100         msq->q_perm.security = NULL;
 101         retval = security_msg_queue_alloc(msq);
 102         if (retval) {
 103                 ipc_rcu_putref(msq);
 104                 return retval;
 105         }
 106
 107         id = ipc_addid(&msg_ids, &msq->q_perm, msg_ctlmni);
 108         if(id == -1) {
 109                 security_msg_queue_free(msq);
 110                 ipc_rcu_putref(msq);
 111                 return -ENOSPC;
 112         }
 113
 114         msq->q_stime = msq->q_rtime = 0;
 115         msq->q_ctime = get_seconds();
 116         msq->q_cbytes = msq->q_qnum = 0;
 117         msq->q_qbytes = msg_ctlmnb;
 118         msq->q_lspid = msq->q_lrpid = 0;
 119         INIT_LIST_HEAD(&msq->q_messages);
 120         INIT_LIST_HEAD(&msq->q_receivers);
 121         INIT_LIST_HEAD(&msq->q_senders);
 122         msg_unlock(msq);
 123
 124         return msg_buildid(id,msq->q_perm.seq);
 125 }
 126
 127 static inline void ss_add(struct msg_queue* msq, struct msg_sender* mss)
 128 {
 129         mss->tsk=current;
 130         current->state=TASK_INTERRUPTIBLE;
 131         list_add_tail(&mss->list,&msq->q_senders);
 132 }
 133
 134 static inline void ss_del(struct msg_sender* mss)
 135 {
 136         if(mss->list.next != NULL)
 137                 list_del(&mss->list);
 138 }
 139
 140 static void ss_wakeup(struct list_head* h, int kill)
 141 {
 142         struct list_head *tmp;
 143
 144         tmp = h->next;
 145         while (tmp != h) {
 146                 struct msg_sender* mss;
 147
 148                 mss = list_entry(tmp,struct msg_sender,list);
 149                 tmp = tmp->next;
 150                 if(kill)
 151                         mss->list.next=NULL;
 152                 wake_up_process(mss->tsk);
 153         }
 154 }
 155
 156 static void expunge_all(struct msg_queue* msq, int res)
 157 {
 158         struct list_head *tmp;
 159
 160         tmp = msq->q_receivers.next;
 161         while (tmp != &msq->q_receivers) {
 162                 struct msg_receiver* msr;
 163
 164                 msr = list_entry(tmp,struct msg_receiver,r_list);
 165                 tmp = tmp->next;
 166                 msr->r_msg = NULL;
 167                 wake_up_process(msr->r_tsk);
 168                 smp_mb();
 169                 msr->r_msg = ERR_PTR(res);
 170         }
 171 }
 172 /*
 173  * freeque() wakes up waiters on the sender and receiver waiting queue,
 174  * removes the message queue from message queue ID
 175  * array, and cleans up all the messages associated with this queue.
 176  *
 177  * msg_ids.sem and the spinlock for this message queue is hold
 178  * before freeque() is called. msg_ids.sem remains locked on exit.
 179  */
 180 static void freeque (struct msg_queue *msq, int id)
 181 {
 182         struct list_head *tmp;
 183
 184         expunge_all(msq,-EIDRM);
 185         ss_wakeup(&msq->q_senders,1);
 186         msq = msg_rmid(id);
 187         msg_unlock(msq);
 188
 189         tmp = msq->q_messages.next;
 190         while(tmp != &msq->q_messages) {
 191                 struct msg_msg* msg = list_entry(tmp,struct msg_msg,m_list);
 192                 tmp = tmp->next;
 193                 atomic_dec(&msg_hdrs);
 194                 free_msg(msg);
 195         }
 196         atomic_sub(msq->q_cbytes, &msg_bytes);
 197         security_msg_queue_free(msq);
 198         ipc_rcu_putref(msq);
 199 }
 200
 201 asmlinkage long sys_msgget (key_t key, int msgflg)
 202 {
 203         int id, ret = -EPERM;
 204         struct msg_queue *msq;
 205
 206         down(&msg_ids.sem);
 207         if (key == IPC_PRIVATE)
 208                 ret = newque(key, msgflg);
 209         else if ((id = ipc_findkey(&msg_ids, key)) == -1) { /* key not used */
 210                 if (!(msgflg & IPC_CREAT))
 211                         ret = -ENOENT;
 212                 else
 213                         ret = newque(key, msgflg);
 214         } else if (msgflg & IPC_CREAT && msgflg & IPC_EXCL) {
 215                 ret = -EEXIST;
 216         } else {
 217                 msq = msg_lock(id);
 218                 if(msq==NULL)
 219                         BUG();
 220                 if (ipcperms(&msq->q_perm, msgflg))
 221                         ret = -EACCES;
 222                 else {
 223                         int qid = msg_buildid(id, msq->q_perm.seq);
 224                         ret = security_msg_queue_associate(msq, msgflg);
 225                         if (!ret)
 226                                 ret = qid;
 227                 }
 228                 msg_unlock(msq);
 229         }
 230         up(&msg_ids.sem);
 231         return ret;
 232 }
 233
 234 static inline unsigned long copy_msqid_to_user(void __user *buf, struct msqid64_ds *in, int version)
 235 {
 236         switch(version) {
 237         case IPC_64:
 238                 return copy_to_user (buf, in, sizeof(*in));
 239         case IPC_OLD:
 240             {
 241                 struct msqid_ds out;
 242
 243                 memset(&out,0,sizeof(out));
 244
 245                 ipc64_perm_to_ipc_perm(&in->msg_perm, &out.msg_perm);
 246
 247                 out.msg_stime           = in->msg_stime;
 248                 out.msg_rtime           = in->msg_rtime;
 249                 out.msg_ctime           = in->msg_ctime;
 250
 251                 if(in->msg_cbytes > USHRT_MAX)
 252                         out.msg_cbytes  = USHRT_MAX;
 253                 else
 254                         out.msg_cbytes  = in->msg_cbytes;
 255                 out.msg_lcbytes         = in->msg_cbytes;
 256
 257                 if(in->msg_qnum > USHRT_MAX)
 258                         out.msg_qnum    = USHRT_MAX;
 259                 else
 260                         out.msg_qnum    = in->msg_qnum;
 261
 262                 if(in->msg_qbytes > USHRT_MAX)
 263                         out.msg_qbytes  = USHRT_MAX;
 264                 else
 265                         out.msg_qbytes  = in->msg_qbytes;
 266                 out.msg_lqbytes         = in->msg_qbytes;
 267
 268                 out.msg_lspid           = in->msg_lspid;
 269                 out.msg_lrpid           = in->msg_lrpid;
 270
 271                 return copy_to_user (buf, &out, sizeof(out));
 272             }
 273         default:
 274                 return -EINVAL;
 275         }
 276 }
 277
 278 struct msq_setbuf {
 279         unsigned long   qbytes;
 280         uid_t           uid;
 281         gid_t           gid;
 282         mode_t          mode;
 283 };
 284
 285 static inline unsigned long copy_msqid_from_user(struct msq_setbuf *out, void __user *buf, int version)
 286 {
 287         switch(version) {
 288         case IPC_64:
 289             {
 290                 struct msqid64_ds tbuf;
 291
 292                 if (copy_from_user (&tbuf, buf, sizeof (tbuf)))
 293                         return -EFAULT;
 294
 295                 out->qbytes             = tbuf.msg_qbytes;
 296                 out->uid                = tbuf.msg_perm.uid;
 297                 out->gid                = tbuf.msg_perm.gid;
 298                 out->mode               = tbuf.msg_perm.mode;
 299
 300                 return 0;
 301             }
 302         case IPC_OLD:
 303             {
 304                 struct msqid_ds tbuf_old;
 305
 306                 if (copy_from_user (&tbuf_old, buf, sizeof (tbuf_old)))
 307                         return -EFAULT;
 308
 309                 out->uid                = tbuf_old.msg_perm.uid;
 310                 out->gid                = tbuf_old.msg_perm.gid;
 311                 out->mode               = tbuf_old.msg_perm.mode;
 312
 313                 if(tbuf_old.msg_qbytes == 0)
 314                         out->qbytes     = tbuf_old.msg_lqbytes;
 315                 else
 316                         out->qbytes     = tbuf_old.msg_qbytes;
 317
 318                 return 0;
 319             }
 320         default:
 321                 return -EINVAL;
 322         }
 323 }
 324
 325 asmlinkage long sys_msgctl (int msqid, int cmd, struct msqid_ds __user *buf)
 326 {
 327         int err, version;
 328         struct msg_queue *msq;
 329         struct msq_setbuf setbuf;
 330         struct kern_ipc_perm *ipcp;
 331
 332         if (msqid < 0 || cmd < 0)
 333                 return -EINVAL;
 334
 335         version = ipc_parse_version(&cmd);
 336
 337         switch (cmd) {
 338         case IPC_INFO:
 339         case MSG_INFO:
 340         {
 341                 struct msginfo msginfo;
 342                 int max_id;
 343                 if (!buf)
 344                         return -EFAULT;
 345                 /* We must not return kernel stack data.
 346                  * due to padding, it's not enough
 347                  * to set all member fields.
 348                  */
 349
 350                 err = security_msg_queue_msgctl(NULL, cmd);
 351                 if (err)
 352                         return err;
 353
 354                 memset(&msginfo,0,sizeof(msginfo));
 355                 msginfo.msgmni = msg_ctlmni;
 356                 msginfo.msgmax = msg_ctlmax;
 357                 msginfo.msgmnb = msg_ctlmnb;
 358                 msginfo.msgssz = MSGSSZ;
 359                 msginfo.msgseg = MSGSEG;
 360                 down(&msg_ids.sem);
 361                 if (cmd == MSG_INFO) {
 362                         msginfo.msgpool = msg_ids.in_use;
 363                         msginfo.msgmap = atomic_read(&msg_hdrs);
 364                         msginfo.msgtql = atomic_read(&msg_bytes);
 365                 } else {
 366                         msginfo.msgmap = MSGMAP;
 367                         msginfo.msgpool = MSGPOOL;
 368                         msginfo.msgtql = MSGTQL;
 369                 }
 370                 max_id = msg_ids.max_id;
 371                 up(&msg_ids.sem);
 372                 if (copy_to_user (buf, &msginfo, sizeof(struct msginfo)))
 373                         return -EFAULT;
 374                 return (max_id < 0) ? 0: max_id;
 375         }
 376         case MSG_STAT:
 377         case IPC_STAT:
 378         {
 379                 struct msqid64_ds tbuf;
 380                 int success_return;
 381                 if (!buf)
 382                         return -EFAULT;
 383                 if(cmd == MSG_STAT && msqid >= msg_ids.size)
 384                         return -EINVAL;
 385
 386                 memset(&tbuf,0,sizeof(tbuf));
 387
 388                 msq = msg_lock(msqid);
 389                 if (msq == NULL)
 390                         return -EINVAL;
 391
 392                 if(cmd == MSG_STAT) {
 393                         success_return = msg_buildid(msqid, msq->q_perm.seq);
 394                 } else {
 395                         err = -EIDRM;
 396                         if (msg_checkid(msq,msqid))
 397                                 goto out_unlock;
 398                         success_return = 0;
 399                 }
 400                 err = -EACCES;
 401                 if (ipcperms (&msq->q_perm, S_IRUGO))
 402                         goto out_unlock;
 403
 404                 err = security_msg_queue_msgctl(msq, cmd);
 405                 if (err)
 406                         goto out_unlock;
 407
 408                 kernel_to_ipc64_perm(&msq->q_perm, &tbuf.msg_perm);
 409                 tbuf.msg_stime  = msq->q_stime;
 410                 tbuf.msg_rtime  = msq->q_rtime;
 411                 tbuf.msg_ctime  = msq->q_ctime;
 412                 tbuf.msg_cbytes = msq->q_cbytes;
 413                 tbuf.msg_qnum   = msq->q_qnum;
 414                 tbuf.msg_qbytes = msq->q_qbytes;
 415                 tbuf.msg_lspid  = msq->q_lspid;
 416                 tbuf.msg_lrpid  = msq->q_lrpid;
 417                 msg_unlock(msq);
 418                 if (copy_msqid_to_user(buf, &tbuf, version))
 419                         return -EFAULT;
 420                 return success_return;
 421         }
 422         case IPC_SET:
 423                 if (!buf)
 424                         return -EFAULT;
 425                 if (copy_msqid_from_user (&setbuf, buf, version))
 426                         return -EFAULT;
 427                 break;
 428         case IPC_RMID:
 429                 break;
 430         default:
 431                 return  -EINVAL;
 432         }
 433
 434         down(&msg_ids.sem);
 435         msq = msg_lock(msqid);
 436         err=-EINVAL;
 437         if (msq == NULL)
 438                 goto out_up;
 439
 440         err = -EIDRM;
 441         if (msg_checkid(msq,msqid))
 442                 goto out_unlock_up;
 443         ipcp = &msq->q_perm;
 444         err = -EPERM;
 445         if (current->euid != ipcp->cuid &&
 446             current->euid != ipcp->uid && !capable(CAP_SYS_ADMIN))
 447             /* We _could_ check for CAP_CHOWN above, but we don't */
 448                 goto out_unlock_up;
 449
 450         err = security_msg_queue_msgctl(msq, cmd);
 451         if (err)
 452                 goto out_unlock_up;
 453
 454         switch (cmd) {
 455         case IPC_SET:
 456         {
 457                 err = -EPERM;
 458                 if (setbuf.qbytes > msg_ctlmnb && !capable(CAP_SYS_RESOURCE))
 459                         goto out_unlock_up;
 460
 461                 msq->q_qbytes = setbuf.qbytes;
 462
 463                 ipcp->uid = setbuf.uid;
 464                 ipcp->gid = setbuf.gid;
 465                 ipcp->mode = (ipcp->mode & ~S_IRWXUGO) |
 466                         (S_IRWXUGO & setbuf.mode);
 467                 msq->q_ctime = get_seconds();
 468                 /* sleeping receivers might be excluded by
 469                  * stricter permissions.
 470                  */
 471                 expunge_all(msq,-EAGAIN);
 472                 /* sleeping senders might be able to send
 473                  * due to a larger queue size.
 474                  */
 475                 ss_wakeup(&msq->q_senders,0);
 476                 msg_unlock(msq);
 477                 break;
 478         }
 479         case IPC_RMID:
 480                 freeque (msq, msqid);
 481                 break;
 482         }
 483         err = 0;
 484 out_up:
 485         up(&msg_ids.sem);
 486         return err;
 487 out_unlock_up:
 488         msg_unlock(msq);
 489         goto out_up;
 490 out_unlock:
 491         msg_unlock(msq);
 492         return err;
 493 }
 494
 495 static int testmsg(struct msg_msg* msg,long type,int mode)
 496 {
 497         switch(mode)
 498         {
 499                 case SEARCH_ANY:
 500                         return 1;
 501                 case SEARCH_LESSEQUAL:
 502                         if(msg->m_type <=type)
 503                                 return 1;
 504                         break;
 505                 case SEARCH_EQUAL:
 506                         if(msg->m_type == type)
 507                                 return 1;
 508                         break;
 509                 case SEARCH_NOTEQUAL:
 510                         if(msg->m_type != type)
 511                                 return 1;
 512                         break;
 513         }
 514         return 0;
 515 }
 516
 517 static inline int pipelined_send(struct msg_queue* msq, struct msg_msg* msg)
 518 {
 519         struct list_head* tmp;
 520
 521         tmp = msq->q_receivers.next;
 522         while (tmp != &msq->q_receivers) {
 523                 struct msg_receiver* msr;
 524                 msr = list_entry(tmp,struct msg_receiver,r_list);
 525                 tmp = tmp->next;
 526                 if(testmsg(msg,msr->r_msgtype,msr->r_mode) &&
 527                    !security_msg_queue_msgrcv(msq, msg, msr->r_tsk, msr->r_msgtype, msr->r_mode)) {
 528                         list_del(&msr->r_list);
 529                         if(msr->r_maxsize < msg->m_ts) {
 530                                 msr->r_msg = NULL;
 531                                 wake_up_process(msr->r_tsk);
 532                                 smp_mb();
 533                                 msr->r_msg = ERR_PTR(-E2BIG);
 534                         } else {
 535                                 msr->r_msg = NULL;
 536                                 msq->q_lrpid = msr->r_tsk->pid;
 537                                 msq->q_rtime = get_seconds();
 538                                 wake_up_process(msr->r_tsk);
 539                                 smp_mb();
 540                                 msr->r_msg = msg;
 541                                 return 1;
 542                         }
 543                 }
 544         }
 545         return 0;
 546 }
 547
 548 asmlinkage long sys_msgsnd (int msqid, struct msgbuf __user *msgp, size_t msgsz, int msgflg)
 549 {
 550         struct msg_queue *msq;
 551         struct msg_msg *msg;
 552         long mtype;
 553         int err;
 554
 555         if (msgsz > msg_ctlmax || (long) msgsz < 0 || msqid < 0)
 556                 return -EINVAL;
 557         if (get_user(mtype, &msgp->mtype))
 558                 return -EFAULT;
 559         if (mtype < 1)
 560                 return -EINVAL;
 561
 562         msg = load_msg(msgp->mtext, msgsz);
 563         if(IS_ERR(msg))
 564                 return PTR_ERR(msg);
 565
 566         msg->m_type = mtype;
 567         msg->m_ts = msgsz;
 568
 569         msq = msg_lock(msqid);
 570         err=-EINVAL;
 571         if(msq==NULL)
 572                 goto out_free;
 573
 574         err= -EIDRM;
 575         if (msg_checkid(msq,msqid))
 576                 goto out_unlock_free;
 577
 578         for (;;) {
 579                 struct msg_sender s;
 580
 581                 err=-EACCES;
 582                 if (ipcperms(&msq->q_perm, S_IWUGO))
 583                         goto out_unlock_free;
 584
 585                 err = security_msg_queue_msgsnd(msq, msg, msgflg);
 586                 if (err)
 587                         goto out_unlock_free;
 588
 589                 if(msgsz + msq->q_cbytes <= msq->q_qbytes &&
 590                                 1 + msq->q_qnum <= msq->q_qbytes) {
 591                         break;
 592                 }
 593
 594                 /* queue full, wait: */
 595                 if(msgflg&IPC_NOWAIT) {
 596                         err=-EAGAIN;
 597                         goto out_unlock_free;
 598                 }
 599                 ss_add(msq, &s);
 600                 ipc_rcu_getref(msq);
 601                 msg_unlock(msq);
 602                 schedule();
 603
 604                 ipc_lock_by_ptr(&msq->q_perm);
 605                 ipc_rcu_putref(msq);
 606                 if (msq->q_perm.deleted) {
 607                         err = -EIDRM;
 608                         goto out_unlock_free;
 609                 }
 610                 ss_del(&s);
 611
 612                 if (signal_pending(current)) {
 613                         err=-ERESTARTNOHAND;
 614                         goto out_unlock_free;
 615                 }
 616         }
 617
 618         msq->q_lspid = current->tgid;
 619         msq->q_stime = get_seconds();
 620
 621         if(!pipelined_send(msq,msg)) {
 622                 /* noone is waiting for this message, enqueue it */
 623                 list_add_tail(&msg->m_list,&msq->q_messages);
 624                 msq->q_cbytes += msgsz;
 625                 msq->q_qnum++;
 626                 atomic_add(msgsz,&msg_bytes);
 627                 atomic_inc(&msg_hdrs);
 628         }
 629
 630         err = 0;
 631         msg = NULL;
 632
 633 out_unlock_free:
 634         msg_unlock(msq);
 635 out_free:
 636         if(msg!=NULL)
 637                 free_msg(msg);
 638         return err;
 639 }
 640
 641 static inline int convert_mode(long* msgtyp, int msgflg)
 642 {
 643         /*
 644          *  find message of correct type.
 645          *  msgtyp = 0 => get first.
 646          *  msgtyp > 0 => get first message of matching type.
 647          *  msgtyp < 0 => get message with least type must be < abs(msgtype).
 648          */
 649         if(*msgtyp==0)
 650                 return SEARCH_ANY;
 651         if(*msgtyp<0) {
 652                 *msgtyp=-(*msgtyp);
 653                 return SEARCH_LESSEQUAL;
 654         }
 655         if(msgflg & MSG_EXCEPT)
 656                 return SEARCH_NOTEQUAL;
 657         return SEARCH_EQUAL;
 658 }
 659
 660 asmlinkage long sys_msgrcv (int msqid, struct msgbuf __user *msgp, size_t msgsz,
 661                             long msgtyp, int msgflg)
 662 {
 663         struct msg_queue *msq;
 664         struct msg_msg *msg;
 665         int mode;
 666
 667         if (msqid < 0 || (long) msgsz < 0)
 668                 return -EINVAL;
 669         mode = convert_mode(&msgtyp,msgflg);
 670
 671         msq = msg_lock(msqid);
 672         if(msq==NULL)
 673                 return -EINVAL;
 674
 675         msg = ERR_PTR(-EIDRM);
 676         if (msg_checkid(msq,msqid))
 677                 goto out_unlock;
 678
 679         for (;;) {
 680                 struct msg_receiver msr_d;
 681                 struct list_head* tmp;
 682
 683                 msg = ERR_PTR(-EACCES);
 684                 if (ipcperms (&msq->q_perm, S_IRUGO))
 685                         goto out_unlock;
 686
 687                 msg = ERR_PTR(-EAGAIN);
 688                 tmp = msq->q_messages.next;
 689                 while (tmp != &msq->q_messages) {
 690                         struct msg_msg *walk_msg;
 691                         walk_msg = list_entry(tmp,struct msg_msg,m_list);
 692                         if(testmsg(walk_msg,msgtyp,mode) &&
 693                            !security_msg_queue_msgrcv(msq, walk_msg, current, msgtyp, mode)) {
 694                                 msg = walk_msg;
 695                                 if(mode == SEARCH_LESSEQUAL && walk_msg->m_type != 1) {
 696                                         msg=walk_msg;
 697                                         msgtyp=walk_msg->m_type-1;
 698                                 } else {
 699                                         msg=walk_msg;
 700                                         break;
 701                                 }
 702                         }
 703                         tmp = tmp->next;
 704                 }
 705                 if(!IS_ERR(msg)) {
 706                         /* Found a suitable message. Unlink it from the queue. */
 707                         if ((msgsz < msg->m_ts) && !(msgflg & MSG_NOERROR)) {
 708                                 msg = ERR_PTR(-E2BIG);
 709                                 goto out_unlock;
 710                         }
 711                         list_del(&msg->m_list);
 712                         msq->q_qnum--;
 713                         msq->q_rtime = get_seconds();
 714                         msq->q_lrpid = current->tgid;
 715                         msq->q_cbytes -= msg->m_ts;
 716                         atomic_sub(msg->m_ts,&msg_bytes);
 717                         atomic_dec(&msg_hdrs);
 718                         ss_wakeup(&msq->q_senders,0);
 719                         msg_unlock(msq);
 720                         break;
 721                 }
 722                 /* No message waiting. Wait for a message */
 723                 if (msgflg & IPC_NOWAIT) {
 724                         msg = ERR_PTR(-ENOMSG);
 725                         goto out_unlock;
 726                 }
 727                 list_add_tail(&msr_d.r_list,&msq->q_receivers);
 728                 msr_d.r_tsk = current;
 729                 msr_d.r_msgtype = msgtyp;
 730                 msr_d.r_mode = mode;
 731                 if(msgflg & MSG_NOERROR)
 732                         msr_d.r_maxsize = INT_MAX;
 733                  else
 734                         msr_d.r_maxsize = msgsz;
 735                 msr_d.r_msg = ERR_PTR(-EAGAIN);
 736                 current->state = TASK_INTERRUPTIBLE;
 737                 msg_unlock(msq);
 738
 739                 schedule();
 740
 741                 /* Lockless receive, part 1:
 742                  * Disable preemption.  We don't hold a reference to the queue
 743                  * and getting a reference would defeat the idea of a lockless
 744                  * operation, thus the code relies on rcu to guarantee the
 745                  * existance of msq:
 746                  * Prior to destruction, expunge_all(-EIRDM) changes r_msg.
 747                  * Thus if r_msg is -EAGAIN, then the queue not yet destroyed.
 748                  * rcu_read_lock() prevents preemption between reading r_msg
 749                  * and the spin_lock() inside ipc_lock_by_ptr().
 750                  */
 751                 rcu_read_lock();
 752
 753                 /* Lockless receive, part 2:
 754                  * Wait until pipelined_send or expunge_all are outside of
 755                  * wake_up_process(). There is a race with exit(), see
 756                  * ipc/mqueue.c for the details.
 757                  */
 758                 msg = (struct msg_msg*) msr_d.r_msg;
 759                 while (msg == NULL) {
 760                         cpu_relax();
 761                         msg = (struct msg_msg*) msr_d.r_msg;
 762                 }
 763
 764                 /* Lockless receive, part 3:
 765                  * If there is a message or an error then accept it without
 766                  * locking.
 767                  */
 768                 if(msg != ERR_PTR(-EAGAIN)) {
 769                         rcu_read_unlock();
 770                         break;
 771                 }
 772
 773                 /* Lockless receive, part 3:
 774                  * Acquire the queue spinlock.
 775                  */
 776                 ipc_lock_by_ptr(&msq->q_perm);
 777                 rcu_read_unlock();
 778
 779                 /* Lockless receive, part 4:
 780                  * Repeat test after acquiring the spinlock.
 781                  */
 782                 msg = (struct msg_msg*)msr_d.r_msg;
 783                 if(msg != ERR_PTR(-EAGAIN))
 784                         goto out_unlock;
 785
 786                 list_del(&msr_d.r_list);
 787                 if (signal_pending(current)) {
 788                         msg = ERR_PTR(-ERESTARTNOHAND);
 789 out_unlock:
 790                         msg_unlock(msq);
 791                         break;
 792                 }
 793         }
 794         if (IS_ERR(msg))
 795                 return PTR_ERR(msg);
 796
 797         msgsz = (msgsz > msg->m_ts) ? msg->m_ts : msgsz;
 798         if (put_user (msg->m_type, &msgp->mtype) ||
 799             store_msg(msgp->mtext, msg, msgsz)) {
 800                     msgsz = -EFAULT;
 801         }
 802         free_msg(msg);
 803         return msgsz;
 804 }
 805
 806 #ifdef CONFIG_PROC_FS
 807 static int sysvipc_msg_read_proc(char *buffer, char **start, off_t offset, int length, int *eof, void *data)
 808 {
 809         off_t pos = 0;
 810         off_t begin = 0;
 811         int i, len = 0;
 812
 813         down(&msg_ids.sem);
 814         len += sprintf(buffer, "       key      msqid perms      cbytes       qnum lspid lrpid   uid   gid  cuid  cgid      stime      rtime      ctime\n");
 815
 816         for(i = 0; i <= msg_ids.max_id; i++) {
 817                 struct msg_queue * msq;
 818                 msq = msg_lock(i);
 819                 if(msq != NULL) {
 820                         len += sprintf(buffer + len, "%10d %10d  %4o  %10lu %10lu %5u %5u %5u %5u %5u %5u %10lu %10lu %10lu\n",
 821                                 msq->q_perm.key,
 822                                 msg_buildid(i,msq->q_perm.seq),
 823                                 msq->q_perm.mode,
 824                                 msq->q_cbytes,
 825                                 msq->q_qnum,
 826                                 msq->q_lspid,
 827                                 msq->q_lrpid,
 828                                 msq->q_perm.uid,
 829                                 msq->q_perm.gid,
 830                                 msq->q_perm.cuid,
 831                                 msq->q_perm.cgid,
 832                                 msq->q_stime,
 833                                 msq->q_rtime,
 834                                 msq->q_ctime);
 835                         msg_unlock(msq);
 836
 837                         pos += len;
 838                         if(pos < offset) {
 839                                 len = 0;
 840                                 begin = pos;
 841                         }
 842                         if(pos > offset + length)
 843                                 goto done;
 844                 }
 845
 846         }
 847         *eof = 1;
 848 done:
 849         up(&msg_ids.sem);
 850         *start = buffer + (offset - begin);
 851         len -= (offset - begin);
 852         if(len > length)
 853                 len = length;
 854         if(len < 0)
 855                 len = 0;
 856         return len;
 857 }
 858 #endif