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