ClabureDB: Classified Bug-Reports Database

   /*
    * linux/ipc/sem.c
    * Copyright (C) 1992 Krishna Balasubramanian
    * Copyright (C) 1995 Eric Schenk, Bruno Haible
    *
    * IMPLEMENTATION NOTES ON CODE REWRITE (Eric Schenk, January 1995):
    * This code underwent a massive rewrite in order to solve some problems
    * with the original code. In particular the original code failed to
    * wake up processes that were waiting for semval to go to 0 if the
   * value went to 0 and was then incremented rapidly enough. In solving
   * this problem I have also modified the implementation so that it
   * processes pending operations in a FIFO manner, thus give a guarantee
   * that processes waiting for a lock on the semaphore won't starve
   * unless another locking process fails to unlock.
   * In addition the following two changes in behavior have been introduced:
   * - The original implementation of semop returned the value
   *   last semaphore element examined on success. This does not
   *   match the manual page specifications, and effectively
   *   allows the user to read the semaphore even if they do not
   *   have read permissions. The implementation now returns 0
   *   on success as stated in the manual page.
   * - There is some confusion over whether the set of undo adjustments
   *   to be performed at exit should be done in an atomic manner.
   *   That is, if we are attempting to decrement the semval should we queue
   *   up and wait until we can do so legally?
   *   The original implementation attempted to do this.
   *   The current implementation does not do so. This is because I don't
   *   think it is the right thing (TM) to do, and because I couldn't
   *   see a clean way to get the old behavior with the new design.
   *   The POSIX standard and SVID should be consulted to determine
   *   what behavior is mandated.
   *
   * Further notes on refinement (Christoph Rohland, December 1998):
   * - The POSIX standard says, that the undo adjustments simply should
   *   redo. So the current implementation is o.K.
   * - The previous code had two flaws:
   *   1) It actively gave the semaphore to the next waiting process
   *      sleeping on the semaphore. Since this process did not have the
   *      cpu this led to many unnecessary context switches and bad
   *      performance. Now we only check which process should be able to
   *      get the semaphore and if this process wants to reduce some
   *      semaphore value we simply wake it up without doing the
   *      operation. So it has to try to get it later. Thus e.g. the
   *      running process may reacquire the semaphore during the current
   *      time slice. If it only waits for zero or increases the semaphore,
   *      we do the operation in advance and wake it up.
   *   2) It did not wake up all zero waiting processes. We try to do
   *      better but only get the semops right which only wait for zero or
   *      increase. If there are decrement operations in the operations
   *      array we do the same as before.
   *
   * With the incarnation of O(1) scheduler, it becomes unnecessary to perform
   * check/retry algorithm for waking up blocked processes as the new scheduler
   * is better at handling thread switch than the old one.
   *
   * /proc/sysvipc/sem support (c) 1999 Dragos Acostachioaie <dragos@iname.com>
   *
   * SMP-threaded, sysctl's added
   * (c) 1999 Manfred Spraul <manfred@colorfullife.com>
   * Enforced range limit on SEM_UNDO
   * (c) 2001 Red Hat Inc <alan@redhat.com>
   * Lockless wakeup
   * (c) 2003 Manfred Spraul <manfred@colorfullife.com>
   *
   * support for audit of ipc object properties and permission changes
   * Dustin Kirkland <dustin.kirkland@us.ibm.com>
   *
   * namespaces support
   * OpenVZ, SWsoft Inc.
   * Pavel Emelianov <xemul@openvz.org>
   */
  
  #include <linux/slab.h>
  #include <linux/spinlock.h>
  #include <linux/init.h>
  #include <linux/proc_fs.h>
  #include <linux/time.h>
  #include <linux/security.h>
  #include <linux/syscalls.h>
  #include <linux/audit.h>
  #include <linux/capability.h>
  #include <linux/seq_file.h>
  #include <linux/rwsem.h>
  #include <linux/nsproxy.h>
  #include <linux/ipc_namespace.h>
  
  #include <asm/uaccess.h>
  #include "util.h"
  
  #define sem_ids(ns)        ((ns)->ids[IPC_SEM_IDS])
  
  #define sem_unlock(sma)                ipc_unlock(&(sma)->sem_perm)
  #define sem_checkid(sma, semid)        ipc_checkid(&sma->sem_perm, semid)
  
  static int newary(struct ipc_namespace *, struct ipc_params *);
  static void freeary(struct ipc_namespace *, struct kern_ipc_perm *);
  #ifdef CONFIG_PROC_FS
  static int sysvipc_sem_proc_show(struct seq_file *s, void *it);
  #endif
 
 #define SEMMSL_FAST        256 /* 512 bytes on stack */
 #define SEMOPM_FAST        64  /* ~ 372 bytes on stack */
 
 /*
  * linked list protection:
  *        sem_undo.id_next,
  *        sem_array.sem_pending{,last},
  *        sem_array.sem_undo: sem_lock() for read/write
  *        sem_undo.proc_next: only "current" is allowed to read/write that field.
  *        
  */
 
 #define sc_semmsl        sem_ctls[0]
 #define sc_semmns        sem_ctls[1]
 #define sc_semopm        sem_ctls[2]
 #define sc_semmni        sem_ctls[3]
 
 void sem_init_ns(struct ipc_namespace *ns)
 {
         ns->sc_semmsl = SEMMSL;
         ns->sc_semmns = SEMMNS;
         ns->sc_semopm = SEMOPM;
         ns->sc_semmni = SEMMNI;
         ns->used_sems = 0;
         ipc_init_ids(&ns->ids[IPC_SEM_IDS]);
 }
 
 #ifdef CONFIG_IPC_NS
 void sem_exit_ns(struct ipc_namespace *ns)
 {
         free_ipcs(ns, &sem_ids(ns), freeary);
 }
 #endif
 
 void __init sem_init (void)
 {
         sem_init_ns(&init_ipc_ns);
         ipc_init_proc_interface("sysvipc/sem",
                                 "       key      semid perms      nsems   uid   gid  cuid  cgid      otime      ctime\n",
                                 IPC_SEM_IDS, sysvipc_sem_proc_show);
 }
 
 /*
  * sem_lock_(check_) routines are called in the paths where the rw_mutex
  * is not held.
  */
 static inline struct sem_array *sem_lock(struct ipc_namespace *ns, int id)
 {
         struct kern_ipc_perm *ipcp = ipc_lock(&sem_ids(ns), id);
 
         if (IS_ERR(ipcp))
                 return (struct sem_array *)ipcp;
 
         return container_of(ipcp, struct sem_array, sem_perm);
 }
 
 static inline struct sem_array *sem_lock_check(struct ipc_namespace *ns,
                                                 int id)
 {
         struct kern_ipc_perm *ipcp = ipc_lock_check(&sem_ids(ns), id);
 
         if (IS_ERR(ipcp))
                 return (struct sem_array *)ipcp;
 
         return container_of(ipcp, struct sem_array, sem_perm);
 }
 
 static inline void sem_lock_and_putref(struct sem_array *sma)
 {
         ipc_lock_by_ptr(&sma->sem_perm);
         ipc_rcu_putref(sma);
 }
 
 static inline void sem_getref_and_unlock(struct sem_array *sma)
 {
         ipc_rcu_getref(sma);
         ipc_unlock(&(sma)->sem_perm);
 }
 
 static inline void sem_putref(struct sem_array *sma)
 {
         ipc_lock_by_ptr(&sma->sem_perm);
         ipc_rcu_putref(sma);
         ipc_unlock(&(sma)->sem_perm);
 }
 
 static inline void sem_rmid(struct ipc_namespace *ns, struct sem_array *s)
 {
         ipc_rmid(&sem_ids(ns), &s->sem_perm);
 }
 
 /*
  * Lockless wakeup algorithm:
  * Without the check/retry algorithm a lockless wakeup is possible:
  * - queue.status is initialized to -EINTR before blocking.
  * - wakeup is performed by
  *        * unlinking the queue entry from sma->sem_pending
  *        * setting queue.status to IN_WAKEUP
  *          This is the notification for the blocked thread that a
  *          result value is imminent.
  *        * call wake_up_process
  *        * set queue.status to the final value.
  * - the previously blocked thread checks queue.status:
  *           * if it's IN_WAKEUP, then it must wait until the value changes
  *           * if it's not -EINTR, then the operation was completed by
  *             update_queue. semtimedop can return queue.status without
  *             performing any operation on the sem array.
  *           * otherwise it must acquire the spinlock and check what's up.
  *
  * The two-stage algorithm is necessary to protect against the following
  * races:
  * - if queue.status is set after wake_up_process, then the woken up idle
  *   thread could race forward and try (and fail) to acquire sma->lock
  *   before update_queue had a chance to set queue.status
  * - if queue.status is written before wake_up_process and if the
  *   blocked process is woken up by a signal between writing
  *   queue.status and the wake_up_process, then the woken up
  *   process could return from semtimedop and die by calling
  *   sys_exit before wake_up_process is called. Then wake_up_process
  *   will oops, because the task structure is already invalid.
  *   (yes, this happened on s390 with sysv msg).
  *
  */
 #define IN_WAKEUP        1
 
 /**
  * newary - Create a new semaphore set
  * @ns: namespace
  * @params: ptr to the structure that contains key, semflg and nsems
  *
  * Called with sem_ids.rw_mutex held (as a writer)
  */
 
 static int newary(struct ipc_namespace *ns, struct ipc_params *params)
 {
         int id;
         int retval;
         struct sem_array *sma;
         int size;
         key_t key = params->key;
         int nsems = params->u.nsems;
         int semflg = params->flg;
 
         if (!nsems)
                 return -EINVAL;
         if (ns->used_sems + nsems > ns->sc_semmns)
                 return -ENOSPC;
 
         size = sizeof (*sma) + nsems * sizeof (struct sem);
         sma = ipc_rcu_alloc(size);
         if (!sma) {
                 return -ENOMEM;
         }
         memset (sma, 0, size);
 
         sma->sem_perm.mode = (semflg & S_IRWXUGO);
         sma->sem_perm.key = key;
 
         sma->sem_perm.security = NULL;
         retval = security_sem_alloc(sma);
         if (retval) {
                 ipc_rcu_putref(sma);
                 return retval;
         }
 
         id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni);
         if (id < 0) {
                 security_sem_free(sma);
                 ipc_rcu_putref(sma);
                 return id;
         }
         ns->used_sems += nsems;
 
         sma->sem_base = (struct sem *) &sma[1];
         INIT_LIST_HEAD(&sma->sem_pending);
         INIT_LIST_HEAD(&sma->list_id);
         sma->sem_nsems = nsems;
         sma->sem_ctime = get_seconds();
         sem_unlock(sma);
 
         return sma->sem_perm.id;
 }
 
 
 /*
  * Called with sem_ids.rw_mutex and ipcp locked.
  */
 static inline int sem_security(struct kern_ipc_perm *ipcp, int semflg)
 {
         struct sem_array *sma;
 
         sma = container_of(ipcp, struct sem_array, sem_perm);
         return security_sem_associate(sma, semflg);
 }
 
 /*
  * Called with sem_ids.rw_mutex and ipcp locked.
  */
 static inline int sem_more_checks(struct kern_ipc_perm *ipcp,
                                 struct ipc_params *params)
 {
         struct sem_array *sma;
 
         sma = container_of(ipcp, struct sem_array, sem_perm);
         if (params->u.nsems > sma->sem_nsems)
                 return -EINVAL;
 
         return 0;
 }
 
 asmlinkage long sys_semget(key_t key, int nsems, int semflg)
 {
         struct ipc_namespace *ns;
         struct ipc_ops sem_ops;
         struct ipc_params sem_params;
 
         ns = current->nsproxy->ipc_ns;
 
         if (nsems < 0 || nsems > ns->sc_semmsl)
                 return -EINVAL;
 
         sem_ops.getnew = newary;
         sem_ops.associate = sem_security;
         sem_ops.more_checks = sem_more_checks;
 
         sem_params.key = key;
         sem_params.flg = semflg;
         sem_params.u.nsems = nsems;
 
         return ipcget(ns, &sem_ids(ns), &sem_ops, &sem_params);
 }
 
 /*
  * Determine whether a sequence of semaphore operations would succeed
  * all at once. Return 0 if yes, 1 if need to sleep, else return error code.
  */
 
 static int try_atomic_semop (struct sem_array * sma, struct sembuf * sops,
                              int nsops, struct sem_undo *un, int pid)
 {
         int result, sem_op;
         struct sembuf *sop;
         struct sem * curr;
 
         for (sop = sops; sop < sops + nsops; sop++) {
                 curr = sma->sem_base + sop->sem_num;
                 sem_op = sop->sem_op;
                 result = curr->semval;
   
                 if (!sem_op && result)
                         goto would_block;
 
                 result += sem_op;
                 if (result < 0)
                         goto would_block;
                 if (result > SEMVMX)
                         goto out_of_range;
                 if (sop->sem_flg & SEM_UNDO) {
                         int undo = un->semadj[sop->sem_num] - sem_op;
                         /*
                           *        Exceeding the undo range is an error.
                          */
                         if (undo < (-SEMAEM - 1) || undo > SEMAEM)
                                 goto out_of_range;
                 }
                 curr->semval = result;
         }
 
         sop--;
         while (sop >= sops) {
                 sma->sem_base[sop->sem_num].sempid = pid;
                 if (sop->sem_flg & SEM_UNDO)
                         un->semadj[sop->sem_num] -= sop->sem_op;
                 sop--;
         }
         
         sma->sem_otime = get_seconds();
         return 0;
 
 out_of_range:
         result = -ERANGE;
         goto undo;
 
 would_block:
         if (sop->sem_flg & IPC_NOWAIT)
                 result = -EAGAIN;
         else
                 result = 1;
 
 undo:
         sop--;
         while (sop >= sops) {
                 sma->sem_base[sop->sem_num].semval -= sop->sem_op;
                 sop--;
         }
 
         return result;
 }
 
 /* Go through the pending queue for the indicated semaphore
  * looking for tasks that can be completed.
  */
 static void update_queue (struct sem_array * sma)
 {
         int error;
         struct sem_queue * q;
 
         q = list_entry(sma->sem_pending.next, struct sem_queue, list);
         while (&q->list != &sma->sem_pending) {
                 error = try_atomic_semop(sma, q->sops, q->nsops,
                                          q->undo, q->pid);
 
                 /* Does q->sleeper still need to sleep? */
                 if (error <= 0) {
                         struct sem_queue *n;
 
                         /*
                          * Continue scanning. The next operation
                          * that must be checked depends on the type of the
                          * completed operation:
                          * - if the operation modified the array, then
                          *   restart from the head of the queue and
                          *   check for threads that might be waiting
                          *   for semaphore values to become 0.
                          * - if the operation didn't modify the array,
                          *   then just continue.
                          * The order of list_del() and reading ->next
                          * is crucial: In the former case, the list_del()
                          * must be done first [because we might be the
                          * first entry in ->sem_pending], in the latter
                          * case the list_del() must be done last
                          * [because the list is invalid after the list_del()]
                          */
                         if (q->alter) {
                                 list_del(&q->list);
                                 n = list_entry(sma->sem_pending.next,
                                                 struct sem_queue, list);
                         } else {
                                 n = list_entry(q->list.next, struct sem_queue,
                                                 list);
                                 list_del(&q->list);
                         }
 
                         /* wake up the waiting thread */
                         q->status = IN_WAKEUP;
 
                         wake_up_process(q->sleeper);
                         /* hands-off: q will disappear immediately after
                          * writing q->status.
                          */
                         smp_wmb();
                         q->status = error;
                         q = n;
                 } else {
                         q = list_entry(q->list.next, struct sem_queue, list);
                 }
         }
 }
 
 /* The following counts are associated to each semaphore:
  *   semncnt        number of tasks waiting on semval being nonzero
  *   semzcnt        number of tasks waiting on semval being zero
  * This model assumes that a task waits on exactly one semaphore.
  * Since semaphore operations are to be performed atomically, tasks actually
  * wait on a whole sequence of semaphores simultaneously.
  * The counts we return here are a rough approximation, but still
  * warrant that semncnt+semzcnt>0 if the task is on the pending queue.
  */
 static int count_semncnt (struct sem_array * sma, ushort semnum)
 {
         int semncnt;
         struct sem_queue * q;
 
         semncnt = 0;
         list_for_each_entry(q, &sma->sem_pending, list) {
                 struct sembuf * sops = q->sops;
                 int nsops = q->nsops;
                 int i;
                 for (i = 0; i < nsops; i++)
                         if (sops[i].sem_num == semnum
                             && (sops[i].sem_op < 0)
                             && !(sops[i].sem_flg & IPC_NOWAIT))
                                 semncnt++;
         }
         return semncnt;
 }
 
 static int count_semzcnt (struct sem_array * sma, ushort semnum)
 {
         int semzcnt;
         struct sem_queue * q;
 
         semzcnt = 0;
         list_for_each_entry(q, &sma->sem_pending, list) {
                 struct sembuf * sops = q->sops;
                 int nsops = q->nsops;
                 int i;
                 for (i = 0; i < nsops; i++)
                         if (sops[i].sem_num == semnum
                             && (sops[i].sem_op == 0)
                             && !(sops[i].sem_flg & IPC_NOWAIT))
                                 semzcnt++;
         }
         return semzcnt;
 }
 
 static void free_un(struct rcu_head *head)
 {
         struct sem_undo *un = container_of(head, struct sem_undo, rcu);
         kfree(un);
 }
 
 /* Free a semaphore set. freeary() is called with sem_ids.rw_mutex locked
  * as a writer and the spinlock for this semaphore set hold. sem_ids.rw_mutex
  * remains locked on exit.
  */
 static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
 {
         struct sem_undo *un, *tu;
         struct sem_queue *q, *tq;
         struct sem_array *sma = container_of(ipcp, struct sem_array, sem_perm);
 
         /* Free the existing undo structures for this semaphore set.  */
         assert_spin_locked(&sma->sem_perm.lock);
         list_for_each_entry_safe(un, tu, &sma->list_id, list_id) {
                 list_del(&un->list_id);
                 spin_lock(&un->ulp->lock);
                 un->semid = -1;
                 list_del_rcu(&un->list_proc);
                 spin_unlock(&un->ulp->lock);
                 call_rcu(&un->rcu, free_un);
         }
 
         /* Wake up all pending processes and let them fail with EIDRM. */
         list_for_each_entry_safe(q, tq, &sma->sem_pending, list) {
                 list_del(&q->list);
 
                 q->status = IN_WAKEUP;
                 wake_up_process(q->sleeper); /* doesn't sleep */
                 smp_wmb();
                 q->status = -EIDRM;        /* hands-off q */
         }
 
         /* Remove the semaphore set from the IDR */
         sem_rmid(ns, sma);
         sem_unlock(sma);
 
         ns->used_sems -= sma->sem_nsems;
         security_sem_free(sma);
         ipc_rcu_putref(sma);
 }
 
 static unsigned long copy_semid_to_user(void __user *buf, struct semid64_ds *in, int version)
 {
         switch(version) {
         case IPC_64:
                 return copy_to_user(buf, in, sizeof(*in));
         case IPC_OLD:
             {
                 struct semid_ds out;
 
                 ipc64_perm_to_ipc_perm(&in->sem_perm, &out.sem_perm);
 
                 out.sem_otime        = in->sem_otime;
                 out.sem_ctime        = in->sem_ctime;
                 out.sem_nsems        = in->sem_nsems;
 
                 return copy_to_user(buf, &out, sizeof(out));
             }
         default:
                 return -EINVAL;
         }
 }
 
 static int semctl_nolock(struct ipc_namespace *ns, int semid,
                          int cmd, int version, union semun arg)
 {
         int err = -EINVAL;
         struct sem_array *sma;
 
         switch(cmd) {
         case IPC_INFO:
         case SEM_INFO:
         {
                 struct seminfo seminfo;
                 int max_id;
 
                 err = security_sem_semctl(NULL, cmd);
                 if (err)
                         return err;
                 
                 memset(&seminfo,0,sizeof(seminfo));
                 seminfo.semmni = ns->sc_semmni;
                 seminfo.semmns = ns->sc_semmns;
                 seminfo.semmsl = ns->sc_semmsl;
                 seminfo.semopm = ns->sc_semopm;
                 seminfo.semvmx = SEMVMX;
                 seminfo.semmnu = SEMMNU;
                 seminfo.semmap = SEMMAP;
                 seminfo.semume = SEMUME;
                 down_read(&sem_ids(ns).rw_mutex);
                 if (cmd == SEM_INFO) {
                         seminfo.semusz = sem_ids(ns).in_use;
                         seminfo.semaem = ns->used_sems;
                 } else {
                         seminfo.semusz = SEMUSZ;
                         seminfo.semaem = SEMAEM;
                 }
                 max_id = ipc_get_maxid(&sem_ids(ns));
                 up_read(&sem_ids(ns).rw_mutex);
                 if (copy_to_user (arg.__buf, &seminfo, sizeof(struct seminfo))) 
                         return -EFAULT;
                 return (max_id < 0) ? 0: max_id;
         }
         case IPC_STAT:
         case SEM_STAT:
         {
                 struct semid64_ds tbuf;
                 int id;
 
                 if (cmd == SEM_STAT) {
                         sma = sem_lock(ns, semid);
                         if (IS_ERR(sma))
                                 return PTR_ERR(sma);
                         id = sma->sem_perm.id;
                 } else {
                         sma = sem_lock_check(ns, semid);
                         if (IS_ERR(sma))
                                 return PTR_ERR(sma);
                         id = 0;
                 }
 
                 err = -EACCES;
                 if (ipcperms (&sma->sem_perm, S_IRUGO))
                         goto out_unlock;
 
                 err = security_sem_semctl(sma, cmd);
                 if (err)
                         goto out_unlock;
 
                 memset(&tbuf, 0, sizeof(tbuf));
 
                 kernel_to_ipc64_perm(&sma->sem_perm, &tbuf.sem_perm);
                 tbuf.sem_otime  = sma->sem_otime;
                 tbuf.sem_ctime  = sma->sem_ctime;
                 tbuf.sem_nsems  = sma->sem_nsems;
                 sem_unlock(sma);
                 if (copy_semid_to_user (arg.buf, &tbuf, version))
                         return -EFAULT;
                 return id;
         }
         default:
                 return -EINVAL;
         }
         return err;
 out_unlock:
         sem_unlock(sma);
         return err;
 }
 
 static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
                 int cmd, int version, union semun arg)
 {
         struct sem_array *sma;
         struct sem* curr;
         int err;
         ushort fast_sem_io[SEMMSL_FAST];
         ushort* sem_io = fast_sem_io;
         int nsems;
 
         sma = sem_lock_check(ns, semid);
         if (IS_ERR(sma))
                 return PTR_ERR(sma);
 
         nsems = sma->sem_nsems;
 
         err = -EACCES;
         if (ipcperms (&sma->sem_perm, (cmd==SETVAL||cmd==SETALL)?S_IWUGO:S_IRUGO))
                 goto out_unlock;
 
         err = security_sem_semctl(sma, cmd);
         if (err)
                 goto out_unlock;
 
         err = -EACCES;
         switch (cmd) {
         case GETALL:
         {
                 ushort __user *array = arg.array;
                 int i;
 
                 if(nsems > SEMMSL_FAST) {
                         sem_getref_and_unlock(sma);
 
                         sem_io = ipc_alloc(sizeof(ushort)*nsems);
                         if(sem_io == NULL) {
                                 sem_putref(sma);
                                 return -ENOMEM;
                         }
 
                         sem_lock_and_putref(sma);
                         if (sma->sem_perm.deleted) {
                                 sem_unlock(sma);
                                 err = -EIDRM;
                                 goto out_free;
                         }
                 }
 
                 for (i = 0; i < sma->sem_nsems; i++)
                         sem_io[i] = sma->sem_base[i].semval;
                 sem_unlock(sma);
                 err = 0;
                 if(copy_to_user(array, sem_io, nsems*sizeof(ushort)))
                         err = -EFAULT;
                 goto out_free;
         }
         case SETALL:
         {
                 int i;
                 struct sem_undo *un;
 
                 sem_getref_and_unlock(sma);
 
                 if(nsems > SEMMSL_FAST) {
                         sem_io = ipc_alloc(sizeof(ushort)*nsems);
                         if(sem_io == NULL) {
                                 sem_putref(sma);
                                 return -ENOMEM;
                         }
                 }
 
                 if (copy_from_user (sem_io, arg.array, nsems*sizeof(ushort))) {
                         sem_putref(sma);
                         err = -EFAULT;
                         goto out_free;
                 }
 
                 for (i = 0; i < nsems; i++) {
                         if (sem_io[i] > SEMVMX) {
                                 sem_putref(sma);
                                 err = -ERANGE;
                                 goto out_free;
                         }
                 }
                 sem_lock_and_putref(sma);
                 if (sma->sem_perm.deleted) {
                         sem_unlock(sma);
                         err = -EIDRM;
                         goto out_free;
                 }
 
                 for (i = 0; i < nsems; i++)
                         sma->sem_base[i].semval = sem_io[i];
 
                 assert_spin_locked(&sma->sem_perm.lock);
                 list_for_each_entry(un, &sma->list_id, list_id) {
                         for (i = 0; i < nsems; i++)
                                 un->semadj[i] = 0;
                 }
                 sma->sem_ctime = get_seconds();
                 /* maybe some queued-up processes were waiting for this */
                 update_queue(sma);
                 err = 0;
                 goto out_unlock;
         }
         /* GETVAL, GETPID, GETNCTN, GETZCNT, SETVAL: fall-through */
         }
         err = -EINVAL;
         if(semnum < 0 || semnum >= nsems)
                 goto out_unlock;
 
         curr = &sma->sem_base[semnum];
 
         switch (cmd) {
         case GETVAL:
                 err = curr->semval;
                 goto out_unlock;
         case GETPID:
                 err = curr->sempid;
                 goto out_unlock;
         case GETNCNT:
                 err = count_semncnt(sma,semnum);
                 goto out_unlock;
         case GETZCNT:
                 err = count_semzcnt(sma,semnum);
                 goto out_unlock;
         case SETVAL:
         {
                 int val = arg.val;
                 struct sem_undo *un;
 
                 err = -ERANGE;
                 if (val > SEMVMX || val < 0)
                         goto out_unlock;
 
                 assert_spin_locked(&sma->sem_perm.lock);
                 list_for_each_entry(un, &sma->list_id, list_id)
                         un->semadj[semnum] = 0;
 
                 curr->semval = val;
                 curr->sempid = task_tgid_vnr(current);
                 sma->sem_ctime = get_seconds();
                 /* maybe some queued-up processes were waiting for this */
                 update_queue(sma);
                 err = 0;
                 goto out_unlock;
         }
         }
 out_unlock:
         sem_unlock(sma);
 out_free:
         if(sem_io != fast_sem_io)
                 ipc_free(sem_io, sizeof(ushort)*nsems);
         return err;
 }
 
 static inline unsigned long
 copy_semid_from_user(struct semid64_ds *out, void __user *buf, int version)
 {
         switch(version) {
         case IPC_64:
                 if (copy_from_user(out, buf, sizeof(*out)))
                         return -EFAULT;
                 return 0;
         case IPC_OLD:
             {
                 struct semid_ds tbuf_old;
 
                 if(copy_from_user(&tbuf_old, buf, sizeof(tbuf_old)))
                         return -EFAULT;
 
                 out->sem_perm.uid        = tbuf_old.sem_perm.uid;
                 out->sem_perm.gid        = tbuf_old.sem_perm.gid;
                 out->sem_perm.mode        = tbuf_old.sem_perm.mode;
 
                 return 0;
             }
         default:
                 return -EINVAL;
         }
 }
 
 /*
  * This function handles some semctl commands which require the rw_mutex
  * to be held in write mode.
  * NOTE: no locks must be held, the rw_mutex is taken inside this function.
  */
 static int semctl_down(struct ipc_namespace *ns, int semid,
                        int cmd, int version, union semun arg)
 {
         struct sem_array *sma;
         int err;
         struct semid64_ds semid64;
         struct kern_ipc_perm *ipcp;
 
         if(cmd == IPC_SET) {
                 if (copy_semid_from_user(&semid64, arg.buf, version))
                         return -EFAULT;
         }
 
         ipcp = ipcctl_pre_down(&sem_ids(ns), semid, cmd, &semid64.sem_perm, 0);
         if (IS_ERR(ipcp))
                 return PTR_ERR(ipcp);
 
         sma = container_of(ipcp, struct sem_array, sem_perm);
 
         err = security_sem_semctl(sma, cmd);
         if (err)
                 goto out_unlock;
 
         switch(cmd){
         case IPC_RMID:
                 freeary(ns, ipcp);
                 goto out_up;
         case IPC_SET:
                 ipc_update_perm(&semid64.sem_perm, ipcp);
                 sma->sem_ctime = get_seconds();
                 break;
         default:
                 err = -EINVAL;
         }
 
 out_unlock:
         sem_unlock(sma);
 out_up:
         up_write(&sem_ids(ns).rw_mutex);
         return err;
 }
 
 asmlinkage long sys_semctl (int semid, int semnum, int cmd, union semun arg)
 {
         int err = -EINVAL;
         int version;
         struct ipc_namespace *ns;
 
         if (semid < 0)
                 return -EINVAL;
 
         version = ipc_parse_version(&cmd);
         ns = current->nsproxy->ipc_ns;
 
         switch(cmd) {
         case IPC_INFO:
         case SEM_INFO:
         case IPC_STAT:
         case SEM_STAT:
                 err = semctl_nolock(ns, semid, cmd, version, arg);
                 return err;
         case GETALL:
         case GETVAL:
         case GETPID:
         case GETNCNT:
         case GETZCNT:
         case SETVAL:
         case SETALL:
                 err = semctl_main(ns,semid,semnum,cmd,version,arg);
                 return err;
         case IPC_RMID:
         case IPC_SET:
                 err = semctl_down(ns, semid, cmd, version, arg);
                 return err;
         default:
                 return -EINVAL;
         }
 }
 
 /* If the task doesn't already have a undo_list, then allocate one
  * here.  We guarantee there is only one thread using this undo list,
  * and current is THE ONE
  *
  * If this allocation and assignment succeeds, but later
  * portions of this code fail, there is no need to free the sem_undo_list.
  * Just let it stay associated with the task, and it'll be freed later
  * at exit time.
  *
  * This can block, so callers must hold no locks.
  */
 static inline int get_undo_list(struct sem_undo_list **undo_listp)
 {
         struct sem_undo_list *undo_list;
 
         undo_list = current->sysvsem.undo_list;
         if (!undo_list) {
                 undo_list = kzalloc(sizeof(*undo_list), GFP_KERNEL);
                 if (undo_list == NULL)
                         return -ENOMEM;
                 spin_lock_init(&undo_list->lock);
                 atomic_set(&undo_list->refcnt, 1);
                 INIT_LIST_HEAD(&undo_list->list_proc);
 
                 current->sysvsem.undo_list = undo_list;
         }
         *undo_listp = undo_list;
         return 0;
 }
 
 static struct sem_undo *lookup_undo(struct sem_undo_list *ulp, int semid)
 {
         struct sem_undo *walk;
 
         list_for_each_entry_rcu(walk, &ulp->list_proc, list_proc) {
                 if (walk->semid == semid)
                         return walk;
         }
         return NULL;
 }
 
 /**
  * find_alloc_undo - Lookup (and if not present create) undo array
  * @ns: namespace
  * @semid: semaphore array id
  *
  * The function looks up (and if not present creates) the undo structure.
  * The size of the undo structure depends on the size of the semaphore
  * array, thus the alloc path is not that straightforward.
  * Lifetime-rules: sem_undo is rcu-protected, on success, the function
  * performs a rcu_read_lock().
  */
 static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
 {
         struct sem_array *sma;
         struct sem_undo_list *ulp;
         struct sem_undo *un, *new;
         int nsems;
         int error;
 
         error = get_undo_list(&ulp);
         if (error)
                 return ERR_PTR(error);
 
         rcu_read_lock();
         spin_lock(&ulp->lock);
         un = lookup_undo(ulp, semid);
         spin_unlock(&ulp->lock);
         if (likely(un!=NULL))
                 goto out;
         rcu_read_unlock();
 
         /* no undo structure around - allocate one. */
        /* step 1: figure out the size of the semaphore array */
        sma = sem_lock_check(ns, semid);
        if (IS_ERR(sma))
                return ERR_PTR(PTR_ERR(sma));

        nsems = sma->sem_nsems;
        sem_getref_and_unlock(sma);

        /* step 2: allocate new undo structure */
        new = kzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems, GFP_KERNEL);
        if (!new) {
                sem_putref(sma);
                return ERR_PTR(-ENOMEM);
        }

        /* step 3: Acquire the lock on semaphore array */
        sem_lock_and_putref(sma);
        if (sma->sem_perm.deleted) {
                sem_unlock(sma);
                kfree(new);
                un = ERR_PTR(-EIDRM);
                goto out;
        }
        spin_lock(&ulp->lock);

        /*
         * step 4: check for races: did someone else allocate the undo struct?
         */
        un = lookup_undo(ulp, semid);
        if (un) {
                kfree(new);
                goto success;
        }
        /* step 5: initialize & link new undo structure */
        new->semadj = (short *) &new[1];
        new->ulp = ulp;
        new->semid = semid;
        assert_spin_locked(&ulp->lock);
        list_add_rcu(&new->list_proc, &ulp->list_proc);
        assert_spin_locked(&sma->sem_perm.lock);
        list_add(&new->list_id, &sma->list_id);
        un = new;

success:
        spin_unlock(&ulp->lock);
        rcu_read_lock();
        sem_unlock(sma);
out:
        return un;
}

asmlinkage long sys_semtimedop(int semid, struct sembuf __user *tsops,
                        unsigned nsops, const struct timespec __user *timeout)
{
        int error = -EINVAL;
        struct sem_array *sma;
        struct sembuf fast_sops[SEMOPM_FAST];
        struct sembuf* sops = fast_sops, *sop;
        struct sem_undo *un;
        int undos = 0, alter = 0, max;
        struct sem_queue queue;
        unsigned long jiffies_left = 0;
        struct ipc_namespace *ns;

        ns = current->nsproxy->ipc_ns;

        if (nsops < 1 || semid < 0)
                return -EINVAL;
        if (nsops > ns->sc_semopm)
                return -E2BIG;
        if(nsops > SEMOPM_FAST) {
                sops = kmalloc(sizeof(*sops)*nsops,GFP_KERNEL);
                if(sops==NULL)
                        return -ENOMEM;
        }
        if (copy_from_user (sops, tsops, nsops * sizeof(*tsops))) {
                error=-EFAULT;
                goto out_free;
        }
        if (timeout) {
                struct timespec _timeout;
                if (copy_from_user(&_timeout, timeout, sizeof(*timeout))) {
                        error = -EFAULT;
                        goto out_free;
                }
                if (_timeout.tv_sec < 0 || _timeout.tv_nsec < 0 ||
                        _timeout.tv_nsec >= 1000000000L) {
                        error = -EINVAL;
                        goto out_free;
                }
                jiffies_left = timespec_to_jiffies(&_timeout);
        }
        max = 0;
        for (sop = sops; sop < sops + nsops; sop++) {
                if (sop->sem_num >= max)
                        max = sop->sem_num;
                if (sop->sem_flg & SEM_UNDO)
                        undos = 1;
                if (sop->sem_op != 0)
                        alter = 1;
        }

        if (undos) {
                un = find_alloc_undo(ns, semid);
                if (IS_ERR(un)) {
                        error = PTR_ERR(un);
                        goto out_free;
                }
        } else
                un = NULL;

        sma = sem_lock_check(ns, semid);
        if (IS_ERR(sma)) {
                if (un)
                        rcu_read_unlock();
                error = PTR_ERR(sma);
                goto out_free;
        }

        /*
         * semid identifiers are not unique - find_alloc_undo may have
         * allocated an undo structure, it was invalidated by an RMID
         * and now a new array with received the same id. Check and fail.
         * This case can be detected checking un->semid. The existance of
         * "un" itself is guaranteed by rcu.
         */
        error = -EIDRM;
        if (un) {
                if (un->semid == -1) {
                        rcu_read_unlock();
                        goto out_unlock_free;
                } else {
                        /*
                         * rcu lock can be released, "un" cannot disappear:
                         * - sem_lock is acquired, thus IPC_RMID is
                         *   impossible.
                         * - exit_sem is impossible, it always operates on
                         *   current (or a dead task).
                         */

                        rcu_read_unlock();
                }
        }

        error = -EFBIG;
        if (max >= sma->sem_nsems)
                goto out_unlock_free;

        error = -EACCES;
        if (ipcperms(&sma->sem_perm, alter ? S_IWUGO : S_IRUGO))
                goto out_unlock_free;

        error = security_sem_semop(sma, sops, nsops, alter);
        if (error)
                goto out_unlock_free;

        error = try_atomic_semop (sma, sops, nsops, un, task_tgid_vnr(current));
        if (error <= 0) {
                if (alter && error == 0)
                        update_queue (sma);
                goto out_unlock_free;
        }

        /* We need to sleep on this operation, so we put the current
         * task into the pending queue and go to sleep.
         */
                
        queue.sops = sops;
        queue.nsops = nsops;
        queue.undo = un;
        queue.pid = task_tgid_vnr(current);
        queue.alter = alter;
        if (alter)
                list_add_tail(&queue.list, &sma->sem_pending);
        else
                list_add(&queue.list, &sma->sem_pending);

        queue.status = -EINTR;
        queue.sleeper = current;
        current->state = TASK_INTERRUPTIBLE;
        sem_unlock(sma);

        if (timeout)
                jiffies_left = schedule_timeout(jiffies_left);
        else
                schedule();

        error = queue.status;
        while(unlikely(error == IN_WAKEUP)) {
                cpu_relax();
                error = queue.status;
        }

        if (error != -EINTR) {
                /* fast path: update_queue already obtained all requested
                 * resources */
                goto out_free;
        }

        sma = sem_lock(ns, semid);
        if (IS_ERR(sma)) {
                error = -EIDRM;
                goto out_free;
        }

        /*
         * If queue.status != -EINTR we are woken up by another process
         */
        error = queue.status;
        if (error != -EINTR) {
                goto out_unlock_free;
        }

        /*
         * If an interrupt occurred we have to clean up the queue
         */
        if (timeout && jiffies_left == 0)
                error = -EAGAIN;
        list_del(&queue.list);
        goto out_unlock_free;

out_unlock_free:
        sem_unlock(sma);
out_free:
        if(sops != fast_sops)
                kfree(sops);
        return error;
}

asmlinkage long sys_semop (int semid, struct sembuf __user *tsops, unsigned nsops)
{
        return sys_semtimedop(semid, tsops, nsops, NULL);
}

/* If CLONE_SYSVSEM is set, establish sharing of SEM_UNDO state between
 * parent and child tasks.
 */

int copy_semundo(unsigned long clone_flags, struct task_struct *tsk)
{
        struct sem_undo_list *undo_list;
        int error;

        if (clone_flags & CLONE_SYSVSEM) {
                error = get_undo_list(&undo_list);
                if (error)
                        return error;
                atomic_inc(&undo_list->refcnt);
                tsk->sysvsem.undo_list = undo_list;
        } else 
                tsk->sysvsem.undo_list = NULL;

        return 0;
}

/*
 * add semadj values to semaphores, free undo structures.
 * undo structures are not freed when semaphore arrays are destroyed
 * so some of them may be out of date.
 * IMPLEMENTATION NOTE: There is some confusion over whether the
 * set of adjustments that needs to be done should be done in an atomic
 * manner or not. That is, if we are attempting to decrement the semval
 * should we queue up and wait until we can do so legally?
 * The original implementation attempted to do this (queue and wait).
 * The current implementation does not do so. The POSIX standard
 * and SVID should be consulted to determine what behavior is mandated.
 */
void exit_sem(struct task_struct *tsk)
{
        struct sem_undo_list *ulp;

        ulp = tsk->sysvsem.undo_list;
        if (!ulp)
                return;
        tsk->sysvsem.undo_list = NULL;

        if (!atomic_dec_and_test(&ulp->refcnt))
                return;

        for (;;) {
                struct sem_array *sma;
                struct sem_undo *un;
                int semid;
                int i;

                rcu_read_lock();
                un = list_entry(rcu_dereference(ulp->list_proc.next),
                                        struct sem_undo, list_proc);
                if (&un->list_proc == &ulp->list_proc)
                        semid = -1;
                 else
                        semid = un->semid;
                rcu_read_unlock();

                if (semid == -1)
                        break;

                sma = sem_lock_check(tsk->nsproxy->ipc_ns, un->semid);

                /* exit_sem raced with IPC_RMID, nothing to do */
                if (IS_ERR(sma))
                        continue;

                un = lookup_undo(ulp, semid);
                if (un == NULL) {
                        /* exit_sem raced with IPC_RMID+semget() that created
                         * exactly the same semid. Nothing to do.
                         */
                        sem_unlock(sma);
                        continue;
                }

                /* remove un from the linked lists */
                assert_spin_locked(&sma->sem_perm.lock);
                list_del(&un->list_id);

                spin_lock(&ulp->lock);
                list_del_rcu(&un->list_proc);
                spin_unlock(&ulp->lock);

                /* perform adjustments registered in un */
                for (i = 0; i < sma->sem_nsems; i++) {
                        struct sem * semaphore = &sma->sem_base[i];
                        if (un->semadj[i]) {
                                semaphore->semval += un->semadj[i];
                                /*
                                 * Range checks of the new semaphore value,
                                 * not defined by sus:
                                 * - Some unices ignore the undo entirely
                                 *   (e.g. HP UX 11i 11.22, Tru64 V5.1)
                                 * - some cap the value (e.g. FreeBSD caps
                                 *   at 0, but doesn't enforce SEMVMX)
                                 *
                                 * Linux caps the semaphore value, both at 0
                                 * and at SEMVMX.
                                 *
                                 *         Manfred <manfred@colorfullife.com>
                                 */
                                if (semaphore->semval < 0)
                                        semaphore->semval = 0;
                                if (semaphore->semval > SEMVMX)
                                        semaphore->semval = SEMVMX;
                                semaphore->sempid = task_tgid_vnr(current);
                        }
                }
                sma->sem_otime = get_seconds();
                /* maybe some queued-up processes were waiting for this */
                update_queue(sma);
                sem_unlock(sma);

                call_rcu(&un->rcu, free_un);
        }
        kfree(ulp);
}

#ifdef CONFIG_PROC_FS
static int sysvipc_sem_proc_show(struct seq_file *s, void *it)
{
        struct sem_array *sma = it;

        return seq_printf(s,
                          "%10d %10d  %4o %10lu %5u %5u %5u %5u %10lu %10lu\n",
                          sma->sem_perm.key,
                          sma->sem_perm.id,
                          sma->sem_perm.mode,
                          sma->sem_nsems,
                          sma->sem_perm.uid,
                          sma->sem_perm.gid,
                          sma->sem_perm.cuid,
                          sma->sem_perm.cgid,
                          sma->sem_otime,
                          sma->sem_ctime);
}
#endif