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 <asm/current.h>
  30 #include <asm/uaccess.h>
  31 #include "util.h"
  32
  33 /* sysctl: */
  34 int msg_ctlmax = MSGMAX;
  35 int msg_ctlmnb = MSGMNB;
  36 int msg_ctlmni = MSGMNI;
  37
  38 /* one msg_receiver structure for each sleeping receiver */
  39 struct msg_receiver {
  40         struct list_head r_list;
  41         struct task_struct* r_tsk;
  42
  43         int r_mode;
  44         long r_msgtype;
  45         long r_maxsize;
  46
  47         struct msg_msg* volatile r_msg;
  48 };
  49
  50 /* one msg_sender for each sleeping sender */
  51 struct msg_sender {
  52         struct list_head list;
  53         struct task_struct* tsk;
  54 };
  55
  56 #define SEARCH_ANY              1
  57 #define SEARCH_EQUAL            2
  58 #define SEARCH_NOTEQUAL         3
  59 #define SEARCH_LESSEQUAL        4
  60
  61 static atomic_t msg_bytes = ATOMIC_INIT(0);
  62 static atomic_t msg_hdrs = ATOMIC_INIT(0);
  63
  64 static struct ipc_ids msg_ids;
  65
  66 #define msg_lock(id)    ((struct msg_queue*)ipc_lock(&msg_ids,id))
  67 #define msg_unlock(msq) ipc_unlock(&(msq)->q_perm)
  68 #define msg_rmid(id)    ((struct msg_queue*)ipc_rmid(&msg_ids,id))
  69 #define msg_checkid(msq, msgid) \
  70         ipc_checkid(&msg_ids,&msq->q_perm,msgid)
  71 #define msg_buildid(id, seq) \
  72         ipc_buildid(&msg_ids, id, seq)
  73
  74 static void freeque (struct msg_queue *msq, int id);
  75 static int newque (key_t key, int msgflg);
  76 #ifdef CONFIG_PROC_FS
  77 static int sysvipc_msg_read_proc(char *buffer, char **start, off_t offset, int length, int *eof, void *data);
  78 #endif
  79
  80 void __init msg_init (void)
  81 {
  82         ipc_init_ids(&msg_ids,msg_ctlmni);
  83
  84 #ifdef CONFIG_PROC_FS
  85         create_proc_read_entry("sysvipc/msg", 0, NULL, sysvipc_msg_read_proc, NULL);
  86 #endif
  87 }
  88
  89 static int newque (key_t key, int msgflg)
  90 {
  91         int id;
  92         int retval;
  93         struct msg_queue *msq;
  94
  95         msq  = ipc_rcu_alloc(sizeof(*msq));
  96         if (!msq)
  97                 return -ENOMEM;
  98
  99         msq->q_perm.mode = (msgflg & S_IRWXUGO);
 100         msq->q_perm.key = key;
 101
 102         msq->q_perm.security = NULL;
 103         retval = security_msg_queue_alloc(msq);
 104         if (retval) {
 105                 ipc_rcu_putref(msq);
 106                 return retval;
 107         }
 108
 109         id = ipc_addid(&msg_ids, &msq->q_perm, msg_ctlmni);
 110         if(id == -1) {
 111                 security_msg_queue_free(msq);
 112                 ipc_rcu_putref(msq);
 113                 return -ENOSPC;
 114         }
 115
 116         msq->q_stime = msq->q_rtime = 0;
 117         msq->q_ctime = get_seconds();
 118         msq->q_cbytes = msq->q_qnum = 0;
 119         msq->q_qbytes = msg_ctlmnb;
 120         msq->q_lspid = msq->q_lrpid = 0;
 121         INIT_LIST_HEAD(&msq->q_messages);
 122         INIT_LIST_HEAD(&msq->q_receivers);
 123         INIT_LIST_HEAD(&msq->q_senders);
 124         msg_unlock(msq);
 125
 126         return msg_buildid(id,msq->q_perm.seq);
 127 }
 128
 129 static inline void ss_add(struct msg_queue* msq, struct msg_sender* mss)
 130 {
 131         mss->tsk=current;
 132         current->state=TASK_INTERRUPTIBLE;
 133         list_add_tail(&mss->list,&msq->q_senders);
 134 }
 135
 136 static inline void ss_del(struct msg_sender* mss)
 137 {
 138         if(mss->list.next != NULL)
 139                 list_del(&mss->list);
 140 }
 141
 142 static void ss_wakeup(struct list_head* h, int kill)
 143 {
 144         struct list_head *tmp;
 145
 146         tmp = h->next;
 147         while (tmp != h) {
 148                 struct msg_sender* mss;
 149
 150                 mss = list_entry(tmp,struct msg_sender,list);
 151                 tmp = tmp->next;
 152                 if(kill)
 153                         mss->list.next=NULL;
 154                 wake_up_process(mss->tsk);
 155         }
 156 }
 157
 158 static void expunge_all(struct msg_queue* msq, int res)
 159 {
 160         struct list_head *tmp;
 161
 162         tmp = msq->q_receivers.next;
 163         while (tmp != &msq->q_receivers) {
 164                 struct msg_receiver* msr;
 165
 166                 msr = list_entry(tmp,struct msg_receiver,r_list);
 167                 tmp = tmp->next;
 168                 msr->r_msg = NULL;
 169                 wake_up_process(msr->r_tsk);
 170                 smp_mb();
 171                 msr->r_msg = ERR_PTR(res);
 172         }
 173 }
 174 /*
 175  * freeque() wakes up waiters on the sender and receiver waiting queue,
 176  * removes the message queue from message queue ID
 177  * array, and cleans up all the messages associated with this queue.
 178  *
 179  * msg_ids.sem and the spinlock for this message queue is hold
 180  * before freeque() is called. msg_ids.sem remains locked on exit.
 181  */
 182 static void freeque (struct msg_queue *msq, int id)
 183 {
 184         struct list_head *tmp;
 185
 186         expunge_all(msq,-EIDRM);
 187         ss_wakeup(&msq->q_senders,1);
 188         msq = msg_rmid(id);
 189         msg_unlock(msq);
 190
 191         tmp = msq->q_messages.next;
 192         while(tmp != &msq->q_messages) {
 193                 struct msg_msg* msg = list_entry(tmp,struct msg_msg,m_list);
 194                 tmp = tmp->next;
 195                 atomic_dec(&msg_hdrs);
 196                 free_msg(msg);
 197         }
 198         atomic_sub(msq->q_cbytes, &msg_bytes);
 199         security_msg_queue_free(msq);
 200         ipc_rcu_putref(msq);
 201 }
 202
 203 asmlinkage long sys_msgget (key_t key, int msgflg)
 204 {
 205         int id, ret = -EPERM;
 206         struct msg_queue *msq;
 207
 208         down(&msg_ids.sem);
 209         if (key == IPC_PRIVATE)
 210                 ret = newque(key, msgflg);
 211         else if ((id = ipc_findkey(&msg_ids, key)) == -1) { /* key not used */
 212                 if (!(msgflg & IPC_CREAT))
 213                         ret = -ENOENT;
 214                 else
 215                         ret = newque(key, msgflg);
 216         } else if (msgflg & IPC_CREAT && msgflg & IPC_EXCL) {
 217                 ret = -EEXIST;
 218         } else {
 219                 msq = msg_lock(id);
 220                 if(msq==NULL)
 221                         BUG();
 222                 if (ipcperms(&msq->q_perm, msgflg))
 223                         ret = -EACCES;
 224                 else {
 225                         int qid = msg_buildid(id, msq->q_perm.seq);
 226                         ret = security_msg_queue_associate(msq, msgflg);
 227                         if (!ret)
 228                                 ret = qid;
 229                 }
 230                 msg_unlock(msq);
 231         }
 232         up(&msg_ids.sem);
 233         return ret;
 234 }
 235
 236 static inline unsigned long copy_msqid_to_user(void __user *buf, struct msqid64_ds *in, int version)
 237 {
 238         switch(version) {
 239         case IPC_64:
 240                 return copy_to_user (buf, in, sizeof(*in));
 241         case IPC_OLD:
 242             {
 243                 struct msqid_ds out;
 244
 245                 memset(&out,0,sizeof(out));
 246
 247                 ipc64_perm_to_ipc_perm(&in->msg_perm, &out.msg_perm);
 248
 249                 out.msg_stime           = in->msg_stime;
 250                 out.msg_rtime           = in->msg_rtime;
 251                 out.msg_ctime           = in->msg_ctime;
 252
 253                 if(in->msg_cbytes > USHRT_MAX)
 254                         out.msg_cbytes  = USHRT_MAX;
 255                 else
 256                         out.msg_cbytes  = in->msg_cbytes;
 257                 out.msg_lcbytes         = in->msg_cbytes;
 258
 259                 if(in->msg_qnum > USHRT_MAX)
 260                         out.msg_qnum    = USHRT_MAX;
 261                 else
 262                         out.msg_qnum    = in->msg_qnum;
 263
 264                 if(in->msg_qbytes > USHRT_MAX)
 265                         out.msg_qbytes  = USHRT_MAX;
 266                 else
 267                         out.msg_qbytes  = in->msg_qbytes;
 268                 out.msg_lqbytes         = in->msg_qbytes;
 269
 270                 out.msg_lspid           = in->msg_lspid;
 271                 out.msg_lrpid           = in->msg_lrpid;
 272
 273                 return copy_to_user (buf, &out, sizeof(out));
 274             }
 275         default:
 276                 return -EINVAL;
 277         }
 278 }
 279
 280 struct msq_setbuf {
 281         unsigned long   qbytes;
 282         uid_t           uid;
 283         gid_t           gid;
 284         mode_t          mode;
 285 };
 286
 287 static inline unsigned long copy_msqid_from_user(struct msq_setbuf *out, void __user *buf, int version)
 288 {
 289         switch(version) {
 290         case IPC_64:
 291             {
 292                 struct msqid64_ds tbuf;
 293
 294                 if (copy_from_user (&tbuf, buf, sizeof (tbuf)))
 295                         return -EFAULT;
 296
 297                 out->qbytes             = tbuf.msg_qbytes;
 298                 out->uid                = tbuf.msg_perm.uid;
 299                 out->gid                = tbuf.msg_perm.gid;
 300                 out->mode               = tbuf.msg_perm.mode;
 301
 302                 return 0;
 303             }
 304         case IPC_OLD:
 305             {
 306                 struct msqid_ds tbuf_old;
 307
 308                 if (copy_from_user (&tbuf_old, buf, sizeof (tbuf_old)))
 309                         return -EFAULT;
 310
 311                 out->uid                = tbuf_old.msg_perm.uid;
 312                 out->gid                = tbuf_old.msg_perm.gid;
 313                 out->mode               = tbuf_old.msg_perm.mode;
 314
 315                 if(tbuf_old.msg_qbytes == 0)
 316                         out->qbytes     = tbuf_old.msg_lqbytes;
 317                 else
 318                         out->qbytes     = tbuf_old.msg_qbytes;
 319
 320                 return 0;
 321             }
 322         default:
 323                 return -EINVAL;
 324         }
 325 }
 326
 327 asmlinkage long sys_msgctl (int msqid, int cmd, struct msqid_ds __user *buf)
 328 {
 329         int err, version;
 330         struct msg_queue *msq;
 331         struct msq_setbuf setbuf;
 332         struct kern_ipc_perm *ipcp;
 333
 334         if (msqid < 0 || cmd < 0)
 335                 return -EINVAL;
 336
 337         version = ipc_parse_version(&cmd);
 338
 339         switch (cmd) {
 340         case IPC_INFO:
 341         case MSG_INFO:
 342         {
 343                 struct msginfo msginfo;
 344                 int max_id;
 345                 if (!buf)
 346                         return -EFAULT;
 347                 /* We must not return kernel stack data.
 348                  * due to padding, it's not enough
 349                  * to set all member fields.
 350                  */
 351
 352                 err = security_msg_queue_msgctl(NULL, cmd);
 353                 if (err)
 354                         return err;
 355
 356                 memset(&msginfo,0,sizeof(msginfo));
 357                 msginfo.msgmni = msg_ctlmni;
 358                 msginfo.msgmax = msg_ctlmax;
 359                 msginfo.msgmnb = msg_ctlmnb;
 360                 msginfo.msgssz = MSGSSZ;
 361                 msginfo.msgseg = MSGSEG;
 362                 down(&msg_ids.sem);
 363                 if (cmd == MSG_INFO) {
 364                         msginfo.msgpool = msg_ids.in_use;
 365                         msginfo.msgmap = atomic_read(&msg_hdrs);
 366                         msginfo.msgtql = atomic_read(&msg_bytes);
 367                 } else {
 368                         msginfo.msgmap = MSGMAP;
 369                         msginfo.msgpool = MSGPOOL;
 370                         msginfo.msgtql = MSGTQL;
 371                 }
 372                 max_id = msg_ids.max_id;
 373                 up(&msg_ids.sem);
 374                 if (copy_to_user (buf, &msginfo, sizeof(struct msginfo)))
 375                         return -EFAULT;
 376                 return (max_id < 0) ? 0: max_id;
 377         }
 378         case MSG_STAT:
 379         case IPC_STAT:
 380         {
 381                 struct msqid64_ds tbuf;
 382                 int success_return;
 383                 if (!buf)
 384                         return -EFAULT;
 385                 if(cmd == MSG_STAT && msqid >= msg_ids.entries->size)
 386                         return -EINVAL;
 387
 388                 memset(&tbuf,0,sizeof(tbuf));
 389
 390                 msq = msg_lock(msqid);
 391                 if (msq == NULL)
 392                         return -EINVAL;
 393
 394                 if(cmd == MSG_STAT) {
 395                         success_return = msg_buildid(msqid, msq->q_perm.seq);
 396                 } else {
 397                         err = -EIDRM;
 398                         if (msg_checkid(msq,msqid))
 399                                 goto out_unlock;
 400                         success_return = 0;
 401                 }
 402                 err = -EACCES;
 403                 if (ipcperms (&msq->q_perm, S_IRUGO))
 404                         goto out_unlock;
 405
 406                 err = security_msg_queue_msgctl(msq, cmd);
 407                 if (err)
 408                         goto out_unlock;
 409
 410                 kernel_to_ipc64_perm(&msq->q_perm, &tbuf.msg_perm);
 411                 tbuf.msg_stime  = msq->q_stime;
 412                 tbuf.msg_rtime  = msq->q_rtime;
 413                 tbuf.msg_ctime  = msq->q_ctime;
 414                 tbuf.msg_cbytes = msq->q_cbytes;
 415                 tbuf.msg_qnum   = msq->q_qnum;
 416                 tbuf.msg_qbytes = msq->q_qbytes;
 417                 tbuf.msg_lspid  = msq->q_lspid;
 418                 tbuf.msg_lrpid  = msq->q_lrpid;
 419                 msg_unlock(msq);
 420                 if (copy_msqid_to_user(buf, &tbuf, version))
 421                         return -EFAULT;
 422                 return success_return;
 423         }
 424         case IPC_SET:
 425                 if (!buf)
 426                         return -EFAULT;
 427                 if (copy_msqid_from_user (&setbuf, buf, version))
 428                         return -EFAULT;
 429                 if ((err = audit_ipc_perms(setbuf.qbytes, setbuf.uid, setbuf.gid, setbuf.mode)))
 430                         return err;
 431                 break;
 432         case IPC_RMID:
 433                 break;
 434         default:
 435                 return  -EINVAL;
 436         }
 437
 438         down(&msg_ids.sem);
 439         msq = msg_lock(msqid);
 440         err=-EINVAL;
 441         if (msq == NULL)
 442                 goto out_up;
 443
 444         err = -EIDRM;
 445         if (msg_checkid(msq,msqid))
 446                 goto out_unlock_up;
 447         ipcp = &msq->q_perm;
 448         err = -EPERM;
 449         if (current->euid != ipcp->cuid &&
 450             current->euid != ipcp->uid && !capable(CAP_SYS_ADMIN))
 451             /* We _could_ check for CAP_CHOWN above, but we don't */
 452                 goto out_unlock_up;
 453
 454         err = security_msg_queue_msgctl(msq, cmd);
 455         if (err)
 456                 goto out_unlock_up;
 457
 458         switch (cmd) {
 459         case IPC_SET:
 460         {
 461                 err = -EPERM;
 462                 if (setbuf.qbytes > msg_ctlmnb && !capable(CAP_SYS_RESOURCE))
 463                         goto out_unlock_up;
 464
 465                 msq->q_qbytes = setbuf.qbytes;
 466
 467                 ipcp->uid = setbuf.uid;
 468                 ipcp->gid = setbuf.gid;
 469                 ipcp->mode = (ipcp->mode & ~S_IRWXUGO) |
 470                         (S_IRWXUGO & setbuf.mode);
 471                 msq->q_ctime = get_seconds();
 472                 /* sleeping receivers might be excluded by
 473                  * stricter permissions.
 474                  */
 475                 expunge_all(msq,-EAGAIN);
 476                 /* sleeping senders might be able to send
 477                  * due to a larger queue size.
 478                  */
 479                 ss_wakeup(&msq->q_senders,0);
 480                 msg_unlock(msq);
 481                 break;
 482         }
 483         case IPC_RMID:
 484                 freeque (msq, msqid);
 485                 break;
 486         }
 487         err = 0;
 488 out_up:
 489         up(&msg_ids.sem);
 490         return err;
 491 out_unlock_up:
 492         msg_unlock(msq);
 493         goto out_up;
 494 out_unlock:
 495         msg_unlock(msq);
 496         return err;
 497 }
 498
 499 static int testmsg(struct msg_msg* msg,long type,int mode)
 500 {
 501         switch(mode)
 502         {
 503                 case SEARCH_ANY:
 504                         return 1;
 505                 case SEARCH_LESSEQUAL:
 506                         if(msg->m_type <=type)
 507                                 return 1;
 508                         break;
 509                 case SEARCH_EQUAL:
 510                         if(msg->m_type == type)
 511                                 return 1;
 512                         break;
 513                 case SEARCH_NOTEQUAL:
 514                         if(msg->m_type != type)
 515                                 return 1;
 516                         break;
 517         }
 518         return 0;
 519 }
 520
 521 static inline int pipelined_send(struct msg_queue* msq, struct msg_msg* msg)
 522 {
 523         struct list_head* tmp;
 524
 525         tmp = msq->q_receivers.next;
 526         while (tmp != &msq->q_receivers) {
 527                 struct msg_receiver* msr;
 528                 msr = list_entry(tmp,struct msg_receiver,r_list);
 529                 tmp = tmp->next;
 530                 if(testmsg(msg,msr->r_msgtype,msr->r_mode) &&
 531                    !security_msg_queue_msgrcv(msq, msg, msr->r_tsk, msr->r_msgtype, msr->r_mode)) {
 532                         list_del(&msr->r_list);
 533                         if(msr->r_maxsize < msg->m_ts) {
 534                                 msr->r_msg = NULL;
 535                                 wake_up_process(msr->r_tsk);
 536                                 smp_mb();
 537                                 msr->r_msg = ERR_PTR(-E2BIG);
 538                         } else {
 539                                 msr->r_msg = NULL;
 540                                 msq->q_lrpid = msr->r_tsk->pid;
 541                                 msq->q_rtime = get_seconds();
 542                                 wake_up_process(msr->r_tsk);
 543                                 smp_mb();
 544                                 msr->r_msg = msg;
 545                                 return 1;
 546                         }
 547                 }
 548         }
 549         return 0;
 550 }
 551
 552 asmlinkage long sys_msgsnd (int msqid, struct msgbuf __user *msgp, size_t msgsz, int msgflg)
 553 {
 554         struct msg_queue *msq;
 555         struct msg_msg *msg;
 556         long mtype;
 557         int err;
 558
 559         if (msgsz > msg_ctlmax || (long) msgsz < 0 || msqid < 0)
 560                 return -EINVAL;
 561         if (get_user(mtype, &msgp->mtype))
 562                 return -EFAULT;
 563         if (mtype < 1)
 564                 return -EINVAL;
 565
 566         msg = load_msg(msgp->mtext, msgsz);
 567         if(IS_ERR(msg))
 568                 return PTR_ERR(msg);
 569
 570         msg->m_type = mtype;
 571         msg->m_ts = msgsz;
 572
 573         msq = msg_lock(msqid);
 574         err=-EINVAL;
 575         if(msq==NULL)
 576                 goto out_free;
 577
 578         err= -EIDRM;
 579         if (msg_checkid(msq,msqid))
 580                 goto out_unlock_free;
 581
 582         for (;;) {
 583                 struct msg_sender s;
 584
 585                 err=-EACCES;
 586                 if (ipcperms(&msq->q_perm, S_IWUGO))
 587                         goto out_unlock_free;
 588
 589                 err = security_msg_queue_msgsnd(msq, msg, msgflg);
 590                 if (err)
 591                         goto out_unlock_free;
 592
 593                 if(msgsz + msq->q_cbytes <= msq->q_qbytes &&
 594                                 1 + msq->q_qnum <= msq->q_qbytes) {
 595                         break;
 596                 }
 597
 598                 /* queue full, wait: */
 599                 if(msgflg&IPC_NOWAIT) {
 600                         err=-EAGAIN;
 601                         goto out_unlock_free;
 602                 }
 603                 ss_add(msq, &s);
 604                 ipc_rcu_getref(msq);
 605                 msg_unlock(msq);
 606                 schedule();
 607
 608                 ipc_lock_by_ptr(&msq->q_perm);
 609                 ipc_rcu_putref(msq);
 610                 if (msq->q_perm.deleted) {
 611                         err = -EIDRM;
 612                         goto out_unlock_free;
 613                 }
 614                 ss_del(&s);
 615
 616                 if (signal_pending(current)) {
 617                         err=-ERESTARTNOHAND;
 618                         goto out_unlock_free;
 619                 }
 620         }
 621
 622         msq->q_lspid = current->tgid;
 623         msq->q_stime = get_seconds();
 624
 625         if(!pipelined_send(msq,msg)) {
 626                 /* noone is waiting for this message, enqueue it */
 627                 list_add_tail(&msg->m_list,&msq->q_messages);
 628                 msq->q_cbytes += msgsz;
 629                 msq->q_qnum++;
 630                 atomic_add(msgsz,&msg_bytes);
 631                 atomic_inc(&msg_hdrs);
 632         }
 633
 634         err = 0;
 635         msg = NULL;
 636
 637 out_unlock_free:
 638         msg_unlock(msq);
 639 out_free:
 640         if(msg!=NULL)
 641                 free_msg(msg);
 642         return err;
 643 }
 644
 645 static inline int convert_mode(long* msgtyp, int msgflg)
 646 {
 647         /*
 648          *  find message of correct type.
 649          *  msgtyp = 0 => get first.
 650          *  msgtyp > 0 => get first message of matching type.
 651          *  msgtyp < 0 => get message with least type must be < abs(msgtype).
 652          */
 653         if(*msgtyp==0)
 654                 return SEARCH_ANY;
 655         if(*msgtyp<0) {
 656                 *msgtyp=-(*msgtyp);
 657                 return SEARCH_LESSEQUAL;
 658         }
 659         if(msgflg & MSG_EXCEPT)
 660                 return SEARCH_NOTEQUAL;
 661         return SEARCH_EQUAL;
 662 }
 663
 664 asmlinkage long sys_msgrcv (int msqid, struct msgbuf __user *msgp, size_t msgsz,
 665                             long msgtyp, int msgflg)
 666 {
 667         struct msg_queue *msq;
 668         struct msg_msg *msg;
 669         int mode;
 670
 671         if (msqid < 0 || (long) msgsz < 0)
 672                 return -EINVAL;
 673         mode = convert_mode(&msgtyp,msgflg);
 674
 675         msq = msg_lock(msqid);
 676         if(msq==NULL)
 677                 return -EINVAL;
 678
 679         msg = ERR_PTR(-EIDRM);
 680         if (msg_checkid(msq,msqid))
 681                 goto out_unlock;
 682
 683         for (;;) {
 684                 struct msg_receiver msr_d;
 685                 struct list_head* tmp;
 686
 687                 msg = ERR_PTR(-EACCES);
 688                 if (ipcperms (&msq->q_perm, S_IRUGO))
 689                         goto out_unlock;
 690
 691                 msg = ERR_PTR(-EAGAIN);
 692                 tmp = msq->q_messages.next;
 693                 while (tmp != &msq->q_messages) {
 694                         struct msg_msg *walk_msg;
 695                         walk_msg = list_entry(tmp,struct msg_msg,m_list);
 696                         if(testmsg(walk_msg,msgtyp,mode) &&
 697                            !security_msg_queue_msgrcv(msq, walk_msg, current, msgtyp, mode)) {
 698                                 msg = walk_msg;
 699                                 if(mode == SEARCH_LESSEQUAL && walk_msg->m_type != 1) {
 700                                         msg=walk_msg;
 701                                         msgtyp=walk_msg->m_type-1;
 702                                 } else {
 703                                         msg=walk_msg;
 704                                         break;
 705                                 }
 706                         }
 707                         tmp = tmp->next;
 708                 }
 709                 if(!IS_ERR(msg)) {
 710                         /* Found a suitable message. Unlink it from the queue. */
 711                         if ((msgsz < msg->m_ts) && !(msgflg & MSG_NOERROR)) {
 712                                 msg = ERR_PTR(-E2BIG);
 713                                 goto out_unlock;
 714                         }
 715                         list_del(&msg->m_list);
 716                         msq->q_qnum--;
 717                         msq->q_rtime = get_seconds();
 718                         msq->q_lrpid = current->tgid;
 719                         msq->q_cbytes -= msg->m_ts;
 720                         atomic_sub(msg->m_ts,&msg_bytes);
 721                         atomic_dec(&msg_hdrs);
 722                         ss_wakeup(&msq->q_senders,0);
 723                         msg_unlock(msq);
 724                         break;
 725                 }
 726                 /* No message waiting. Wait for a message */
 727                 if (msgflg & IPC_NOWAIT) {
 728                         msg = ERR_PTR(-ENOMSG);
 729                         goto out_unlock;
 730                 }
 731                 list_add_tail(&msr_d.r_list,&msq->q_receivers);
 732                 msr_d.r_tsk = current;
 733                 msr_d.r_msgtype = msgtyp;
 734                 msr_d.r_mode = mode;
 735                 if(msgflg & MSG_NOERROR)
 736                         msr_d.r_maxsize = INT_MAX;
 737                  else
 738                         msr_d.r_maxsize = msgsz;
 739                 msr_d.r_msg = ERR_PTR(-EAGAIN);
 740                 current->state = TASK_INTERRUPTIBLE;
 741                 msg_unlock(msq);
 742
 743                 schedule();
 744
 745                 /* Lockless receive, part 1:
 746                  * Disable preemption.  We don't hold a reference to the queue
 747                  * and getting a reference would defeat the idea of a lockless
 748                  * operation, thus the code relies on rcu to guarantee the
 749                  * existance of msq:
 750                  * Prior to destruction, expunge_all(-EIRDM) changes r_msg.
 751                  * Thus if r_msg is -EAGAIN, then the queue not yet destroyed.
 752                  * rcu_read_lock() prevents preemption between reading r_msg
 753                  * and the spin_lock() inside ipc_lock_by_ptr().
 754                  */
 755                 rcu_read_lock();
 756
 757                 /* Lockless receive, part 2:
 758                  * Wait until pipelined_send or expunge_all are outside of
 759                  * wake_up_process(). There is a race with exit(), see
 760                  * ipc/mqueue.c for the details.
 761                  */
 762                 msg = (struct msg_msg*) msr_d.r_msg;
 763                 while (msg == NULL) {
 764                         cpu_relax();
 765                         msg = (struct msg_msg*) msr_d.r_msg;
 766                 }
 767
 768                 /* Lockless receive, part 3:
 769                  * If there is a message or an error then accept it without
 770                  * locking.
 771                  */
 772                 if(msg != ERR_PTR(-EAGAIN)) {
 773                         rcu_read_unlock();
 774                         break;
 775                 }
 776
 777                 /* Lockless receive, part 3:
 778                  * Acquire the queue spinlock.
 779                  */
 780                 ipc_lock_by_ptr(&msq->q_perm);
 781                 rcu_read_unlock();
 782
 783                 /* Lockless receive, part 4:
 784                  * Repeat test after acquiring the spinlock.
 785                  */
 786                 msg = (struct msg_msg*)msr_d.r_msg;
 787                 if(msg != ERR_PTR(-EAGAIN))
 788                         goto out_unlock;
 789
 790                 list_del(&msr_d.r_list);
 791                 if (signal_pending(current)) {
 792                         msg = ERR_PTR(-ERESTARTNOHAND);
 793 out_unlock:
 794                         msg_unlock(msq);
 795                         break;
 796                 }
 797         }
 798         if (IS_ERR(msg))
 799                 return PTR_ERR(msg);
 800
 801         msgsz = (msgsz > msg->m_ts) ? msg->m_ts : msgsz;
 802         if (put_user (msg->m_type, &msgp->mtype) ||
 803             store_msg(msgp->mtext, msg, msgsz)) {
 804                     msgsz = -EFAULT;
 805         }
 806         free_msg(msg);
 807         return msgsz;
 808 }
 809
 810 #ifdef CONFIG_PROC_FS
 811 static int sysvipc_msg_read_proc(char *buffer, char **start, off_t offset, int length, int *eof, void *data)
 812 {
 813         off_t pos = 0;
 814         off_t begin = 0;
 815         int i, len = 0;
 816
 817         down(&msg_ids.sem);
 818         len += sprintf(buffer, "       key      msqid perms      cbytes       qnum lspid lrpid   uid   gid  cuid  cgid      stime      rtime      ctime\n");
 819
 820         for(i = 0; i <= msg_ids.max_id; i++) {
 821                 struct msg_queue * msq;
 822                 msq = msg_lock(i);
 823                 if(msq != NULL) {
 824                         len += sprintf(buffer + len, "%10d %10d  %4o  %10lu %10lu %5u %5u %5u %5u %5u %5u %10lu %10lu %10lu\n",
 825                                 msq->q_perm.key,
 826                                 msg_buildid(i,msq->q_perm.seq),
 827                                 msq->q_perm.mode,
 828                                 msq->q_cbytes,
 829                                 msq->q_qnum,
 830                                 msq->q_lspid,
 831                                 msq->q_lrpid,
 832                                 msq->q_perm.uid,
 833                                 msq->q_perm.gid,
 834                                 msq->q_perm.cuid,
 835                                 msq->q_perm.cgid,
 836                                 msq->q_stime,
 837                                 msq->q_rtime,
 838                                 msq->q_ctime);
 839                         msg_unlock(msq);
 840
 841                         pos += len;
 842                         if(pos < offset) {
 843                                 len = 0;
 844                                 begin = pos;
 845                         }
 846                         if(pos > offset + length)
 847                                 goto done;
 848                 }
 849
 850         }
 851         *eof = 1;
 852 done:
 853         up(&msg_ids.sem);
 854         *start = buffer + (offset - begin);
 855         len -= (offset - begin);
 856         if(len > length)
 857                 len = length;
 858         if(len < 0)
 859                 len = 0;
 860         return len;
 861 }
 862 #endif