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