text: /*
   * linux/ipc/shm.c
   * Copyright (C) 1992, 1993 Krishna Balasubramanian
   *	 Many improvements/fixes by Bruno Haible.
   * Replaced `struct shm_desc' by `struct vm_area_struct', July 1994.
   * Fixed the shm swap deallocation (shm_unuse()), August 1998 Andrea Arcangeli.
   *
   * /proc/sysvipc/shm support (c) 1999 Dragos Acostachioaie <dragos@iname.com>
   * BIGMEM support, Andrea Arcangeli <andrea@suse.de>
   * SMP thread shm, Jean-Luc Boyard <jean-luc.boyard@siemens.fr>
   * HIGHMEM support, Ingo Molnar <mingo@redhat.com>
   * Make shmmax, shmall, shmmni sysctl'able, Christoph Rohland <cr@sap.com>
   * Shared /dev/zero support, Kanoj Sarcar <kanoj@sgi.com>
   * Move the mm functionality over to mm/shmem.c, Christoph Rohland <cr@sap.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/mm.h>
  #include <linux/hugetlb.h>
  #include <linux/shm.h>
  #include <linux/init.h>
  #include <linux/file.h>
  #include <linux/mman.h>
  #include <linux/shmem_fs.h>
  #include <linux/security.h>
  #include <linux/syscalls.h>
  #include <linux/audit.h>
  #include <linux/capability.h>
  #include <linux/ptrace.h>
  #include <linux/seq_file.h>
  #include <linux/rwsem.h>
  #include <linux/nsproxy.h>
  #include <linux/mount.h>
  #include <linux/ipc_namespace.h>
  
  #include <asm/uaccess.h>
  
  #include "util.h"
  
  struct shm_file_data {
  	int id;
  	struct ipc_namespace *ns;
  	struct file *file;
  	const struct vm_operations_struct *vm_ops;
  };
  
  #define shm_file_data(file) (*((struct shm_file_data **)&(file)->private_data))
  
  static const struct file_operations shm_file_operations;
  static const struct vm_operations_struct shm_vm_ops;
  
  #define shm_ids(ns)	((ns)->ids[IPC_SHM_IDS])
  
  #define shm_unlock(shp)			\
  	ipc_unlock(&(shp)->shm_perm)
  
  static int newseg(struct ipc_namespace *, struct ipc_params *);
  static void shm_open(struct vm_area_struct *vma);
  static void shm_close(struct vm_area_struct *vma);
  static void shm_destroy (struct ipc_namespace *ns, struct shmid_kernel *shp);
  #ifdef CONFIG_PROC_FS
  static int sysvipc_shm_proc_show(struct seq_file *s, void *it);
  #endif
  
  void shm_init_ns(struct ipc_namespace *ns)
  {
  	ns->shm_ctlmax = SHMMAX;
  	ns->shm_ctlall = SHMALL;
  	ns->shm_ctlmni = SHMMNI;
  	ns->shm_rmid_forced = 0;
  	ns->shm_tot = 0;
  	ipc_init_ids(&shm_ids(ns));
  }
  
  /*
   * Called with shm_ids.rw_mutex (writer) and the shp structure locked.
   * Only shm_ids.rw_mutex remains locked on exit.
   */
  static void do_shm_rmid(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
  {
  	struct shmid_kernel *shp;
  	shp = container_of(ipcp, struct shmid_kernel, shm_perm);
  
  	if (shp->shm_nattch){
  		shp->shm_perm.mode |= SHM_DEST;
  		/* Do not find it any more */
  		shp->shm_perm.key = IPC_PRIVATE;
  		shm_unlock(shp);
  	} else
  		shm_destroy(ns, shp);
  }
  
  #ifdef CONFIG_IPC_NS
  void shm_exit_ns(struct ipc_namespace *ns)
  {
  	free_ipcs(ns, &shm_ids(ns), do_shm_rmid);
  	idr_destroy(&ns->ids[IPC_SHM_IDS].ipcs_idr);
  }
  #endif
  
  static int __init ipc_ns_init(void)
  {
  	shm_init_ns(&init_ipc_ns);
  	return 0;
  }
  
  pure_initcall(ipc_ns_init);
  
  void __init shm_init (void)
  {
  	ipc_init_proc_interface("sysvipc/shm",
  #if BITS_PER_LONG <= 32
  				"       key      shmid perms       size  cpid  lpid nattch   uid   gid  cuid  cgid      atime      dtime      ctime        rss       swap\n",
  #else
  				"       key      shmid perms                  size  cpid  lpid nattch   uid   gid  cuid  cgid      atime      dtime      ctime                   rss                  swap\n",
  #endif
  				IPC_SHM_IDS, sysvipc_shm_proc_show);
  }
  
  /*
   * shm_lock_(check_) routines are called in the paths where the rw_mutex
   * is not necessarily held.
   */
  static inline struct shmid_kernel *shm_lock(struct ipc_namespace *ns, int id)
  {
  	struct kern_ipc_perm *ipcp = ipc_lock(&shm_ids(ns), id);
  
  	if (IS_ERR(ipcp))
  		return (struct shmid_kernel *)ipcp;
  
  	return container_of(ipcp, struct shmid_kernel, shm_perm);
  }
  
  static inline void shm_lock_by_ptr(struct shmid_kernel *ipcp)
  {
  	rcu_read_lock();
  	spin_lock(&ipcp->shm_perm.lock);
  }
  
  static inline struct shmid_kernel *shm_lock_check(struct ipc_namespace *ns,
  						int id)
  {
  	struct kern_ipc_perm *ipcp = ipc_lock_check(&shm_ids(ns), id);
  
  	if (IS_ERR(ipcp))
  		return (struct shmid_kernel *)ipcp;
  
  	return container_of(ipcp, struct shmid_kernel, shm_perm);
  }
  
  static inline void shm_rmid(struct ipc_namespace *ns, struct shmid_kernel *s)
  {
  	ipc_rmid(&shm_ids(ns), &s->shm_perm);
  }
  
  
  /* This is called by fork, once for every shm attach. */
  static void shm_open(struct vm_area_struct *vma)
  {
  	struct file *file = vma->vm_file;
  	struct shm_file_data *sfd = shm_file_data(file);
  	struct shmid_kernel *shp;
  
  	shp = shm_lock(sfd->ns, sfd->id);
  	BUG_ON(IS_ERR(shp));
  	shp->shm_atim = get_seconds();
  	shp->shm_lprid = task_tgid_vnr(current);
  	shp->shm_nattch++;
  	shm_unlock(shp);
  }
  
  /*
   * shm_destroy - free the struct shmid_kernel
   *
   * @ns: namespace
   * @shp: struct to free
   *
   * It has to be called with shp and shm_ids.rw_mutex (writer) locked,
   * but returns with shp unlocked and freed.
   */
  static void shm_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp)
  {
  	ns->shm_tot -= (shp->shm_segsz + PAGE_SIZE - 1) >> PAGE_SHIFT;
  	shm_rmid(ns, shp);
  	shm_unlock(shp);
  	if (!is_file_hugepages(shp->shm_file))
  		shmem_lock(shp->shm_file, 0, shp->mlock_user);
  	else if (shp->mlock_user)
  		user_shm_unlock(shp->shm_file->f_path.dentry->d_inode->i_size,
  						shp->mlock_user);
  	fput (shp->shm_file);
  	security_shm_free(shp);
  	ipc_rcu_putref(shp);
  }
  
  /*
   * shm_may_destroy - identifies whether shm segment should be destroyed now
   *
   * Returns true if and only if there are no active users of the segment and
   * one of the following is true:
   *
   * 1) shmctl(id, IPC_RMID, NULL) was called for this shp
   *
   * 2) sysctl kernel.shm_rmid_forced is set to 1.
   */
  static bool shm_may_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp)
  {
  	return (shp->shm_nattch == 0) &&
  	       (ns->shm_rmid_forced ||
  		(shp->shm_perm.mode & SHM_DEST));
  }
  
  /*
   * remove the attach descriptor vma.
   * free memory for segment if it is marked destroyed.
   * The descriptor has already been removed from the current->mm->mmap list
   * and will later be kfree()d.
   */
  static void shm_close(struct vm_area_struct *vma)
  {
  	struct file * file = vma->vm_file;
  	struct shm_file_data *sfd = shm_file_data(file);
  	struct shmid_kernel *shp;
  	struct ipc_namespace *ns = sfd->ns;
  
  	down_write(&shm_ids(ns).rw_mutex);
  	/* remove from the list of attaches of the shm segment */
  	shp = shm_lock(ns, sfd->id);
  	BUG_ON(IS_ERR(shp));
  	shp->shm_lprid = task_tgid_vnr(current);
  	shp->shm_dtim = get_seconds();
  	shp->shm_nattch--;
  	if (shm_may_destroy(ns, shp))
  		shm_destroy(ns, shp);
  	else
  		shm_unlock(shp);
  	up_write(&shm_ids(ns).rw_mutex);
  }
  
  /* Called with ns->shm_ids(ns).rw_mutex locked */
  static int shm_try_destroy_current(int id, void *p, void *data)
  {
  	struct ipc_namespace *ns = data;
  	struct kern_ipc_perm *ipcp = p;
  	struct shmid_kernel *shp = container_of(ipcp, struct shmid_kernel, shm_perm);
  
  	if (shp->shm_creator != current)
  		return 0;
  
  	/*
  	 * Mark it as orphaned to destroy the segment when
  	 * kernel.shm_rmid_forced is changed.
  	 * It is noop if the following shm_may_destroy() returns true.
  	 */
  	shp->shm_creator = NULL;
  
  	/*
  	 * Don't even try to destroy it.  If shm_rmid_forced=0 and IPC_RMID
  	 * is not set, it shouldn't be deleted here.
  	 */
  	if (!ns->shm_rmid_forced)
  		return 0;
  
  	if (shm_may_destroy(ns, shp)) {
  		shm_lock_by_ptr(shp);
  		shm_destroy(ns, shp);
  	}
  	return 0;
  }
  
  /* Called with ns->shm_ids(ns).rw_mutex locked */
  static int shm_try_destroy_orphaned(int id, void *p, void *data)
  {
  	struct ipc_namespace *ns = data;
  	struct kern_ipc_perm *ipcp = p;
  	struct shmid_kernel *shp = container_of(ipcp, struct shmid_kernel, shm_perm);
  
  	/*
  	 * We want to destroy segments without users and with already
  	 * exit'ed originating process.
  	 *
  	 * As shp->* are changed under rw_mutex, it's safe to skip shp locking.
  	 */
  	if (shp->shm_creator != NULL)
  		return 0;
  
  	if (shm_may_destroy(ns, shp)) {
  		shm_lock_by_ptr(shp);
  		shm_destroy(ns, shp);
  	}
  	return 0;
  }
  
  void shm_destroy_orphaned(struct ipc_namespace *ns)
  {
  	down_write(&shm_ids(ns).rw_mutex);
  	if (shm_ids(ns).in_use)
  		idr_for_each(&shm_ids(ns).ipcs_idr, &shm_try_destroy_orphaned, ns);
  	up_write(&shm_ids(ns).rw_mutex);
  }
  
  
  void exit_shm(struct task_struct *task)
  {
  	struct ipc_namespace *ns = task->nsproxy->ipc_ns;
  
  	if (shm_ids(ns).in_use == 0)
  		return;
  
  	/* Destroy all already created segments, but not mapped yet */
  	down_write(&shm_ids(ns).rw_mutex);
  	if (shm_ids(ns).in_use)
  		idr_for_each(&shm_ids(ns).ipcs_idr, &shm_try_destroy_current, ns);
  	up_write(&shm_ids(ns).rw_mutex);
  }
  
  static int shm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
  {
  	struct file *file = vma->vm_file;
  	struct shm_file_data *sfd = shm_file_data(file);
  
  	return sfd->vm_ops->fault(vma, vmf);
  }
  
  #ifdef CONFIG_NUMA
  static int shm_set_policy(struct vm_area_struct *vma, struct mempolicy *new)
  {
  	struct file *file = vma->vm_file;
  	struct shm_file_data *sfd = shm_file_data(file);
  	int err = 0;
  	if (sfd->vm_ops->set_policy)
  		err = sfd->vm_ops->set_policy(vma, new);
  	return err;
  }
  
  static struct mempolicy *shm_get_policy(struct vm_area_struct *vma,
  					unsigned long addr)
  {
  	struct file *file = vma->vm_file;
  	struct shm_file_data *sfd = shm_file_data(file);
  	struct mempolicy *pol = NULL;
  
  	if (sfd->vm_ops->get_policy)
  		pol = sfd->vm_ops->get_policy(vma, addr);
  	else if (vma->vm_policy)
  		pol = vma->vm_policy;
  
  	return pol;
  }
  #endif
  
  static int shm_mmap(struct file * file, struct vm_area_struct * vma)
  {
  	struct shm_file_data *sfd = shm_file_data(file);
  	int ret;
  
  	ret = sfd->file->f_op->mmap(sfd->file, vma);
  	if (ret != 0)
  		return ret;
  	sfd->vm_ops = vma->vm_ops;
  #ifdef CONFIG_MMU
  	BUG_ON(!sfd->vm_ops->fault);
  #endif
  	vma->vm_ops = &shm_vm_ops;
  	shm_open(vma);
  
  	return ret;
  }
  
  static int shm_release(struct inode *ino, struct file *file)
  {
  	struct shm_file_data *sfd = shm_file_data(file);
  
  	put_ipc_ns(sfd->ns);
  	shm_file_data(file) = NULL;
  	kfree(sfd);
  	return 0;
  }
  
  static int shm_fsync(struct file *file, loff_t start, loff_t end, int datasync)
  {
  	struct shm_file_data *sfd = shm_file_data(file);
  
  	if (!sfd->file->f_op->fsync)
  		return -EINVAL;
  	return sfd->file->f_op->fsync(sfd->file, start, end, datasync);
  }
  
  static unsigned long shm_get_unmapped_area(struct file *file,
  	unsigned long addr, unsigned long len, unsigned long pgoff,
  	unsigned long flags)
  {
  	struct shm_file_data *sfd = shm_file_data(file);
  	return sfd->file->f_op->get_unmapped_area(sfd->file, addr, len,
  						pgoff, flags);
  }
  
  static const struct file_operations shm_file_operations = {
  	.mmap		= shm_mmap,
  	.fsync		= shm_fsync,
  	.release	= shm_release,
  #ifndef CONFIG_MMU
  	.get_unmapped_area	= shm_get_unmapped_area,
  #endif
  	.llseek		= noop_llseek,
  };
  
  static const struct file_operations shm_file_operations_huge = {
  	.mmap		= shm_mmap,
  	.fsync		= shm_fsync,
  	.release	= shm_release,
  	.get_unmapped_area	= shm_get_unmapped_area,
  	.llseek		= noop_llseek,
  };
  
  int is_file_shm_hugepages(struct file *file)
  {
  	return file->f_op == &shm_file_operations_huge;
  }
  
  static const struct vm_operations_struct shm_vm_ops = {
  	.open	= shm_open,	/* callback for a new vm-area open */
  	.close	= shm_close,	/* callback for when the vm-area is released */
  	.fault	= shm_fault,
  #if defined(CONFIG_NUMA)
  	.set_policy = shm_set_policy,
  	.get_policy = shm_get_policy,
  #endif
  };
  
  /**
   * newseg - Create a new shared memory segment
   * @ns: namespace
   * @params: ptr to the structure that contains key, size and shmflg
   *
   * Called with shm_ids.rw_mutex held as a writer.
   */
  
  static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
  {
  	key_t key = params->key;
  	int shmflg = params->flg;
  	size_t size = params->u.size;
  	int error;
  	struct shmid_kernel *shp;
  	int numpages = (size + PAGE_SIZE -1) >> PAGE_SHIFT;
  	struct file * file;
  	char name[13];
  	int id;
  	vm_flags_t acctflag = 0;
  
  	if (size < SHMMIN || size > ns->shm_ctlmax)
  		return -EINVAL;
  
  	if (ns->shm_tot + numpages > ns->shm_ctlall)
  		return -ENOSPC;
  
  	shp = ipc_rcu_alloc(sizeof(*shp));
  	if (!shp)
  		return -ENOMEM;
  
  	shp->shm_perm.key = key;
  	shp->shm_perm.mode = (shmflg & S_IRWXUGO);
  	shp->mlock_user = NULL;
  
  	shp->shm_perm.security = NULL;
  	error = security_shm_alloc(shp);
  	if (error) {
  		ipc_rcu_putref(shp);
  		return error;
  	}
  
  	sprintf (name, "SYSV%08x", key);
  	if (shmflg & SHM_HUGETLB) {
  		/* hugetlb_file_setup applies strict accounting */
  		if (shmflg & SHM_NORESERVE)
  			acctflag = VM_NORESERVE;
  		file = hugetlb_file_setup(name, size, acctflag,
  					&shp->mlock_user, HUGETLB_SHMFS_INODE);
  	} else {
  		/*
  		 * Do not allow no accounting for OVERCOMMIT_NEVER, even
  	 	 * if it's asked for.
  		 */
  		if  ((shmflg & SHM_NORESERVE) &&
  				sysctl_overcommit_memory != OVERCOMMIT_NEVER)
  			acctflag = VM_NORESERVE;
  		file = shmem_file_setup(name, size, acctflag);
  	}
  	error = PTR_ERR(file);
  	if (IS_ERR(file))
  		goto no_file;
  
  	id = ipc_addid(&shm_ids(ns), &shp->shm_perm, ns->shm_ctlmni);
  	if (id < 0) {
  		error = id;
  		goto no_id;
  	}
  
  	shp->shm_cprid = task_tgid_vnr(current);
  	shp->shm_lprid = 0;
  	shp->shm_atim = shp->shm_dtim = 0;
  	shp->shm_ctim = get_seconds();
  	shp->shm_segsz = size;
  	shp->shm_nattch = 0;
  	shp->shm_file = file;
  	shp->shm_creator = current;
  	/*
  	 * shmid gets reported as "inode#" in /proc/pid/maps.
  	 * proc-ps tools use this. Changing this will break them.
  	 */
  	file->f_dentry->d_inode->i_ino = shp->shm_perm.id;
  
  	ns->shm_tot += numpages;
  	error = shp->shm_perm.id;
  	shm_unlock(shp);
  	return error;
  
  no_id:
  	if (is_file_hugepages(file) && shp->mlock_user)
  		user_shm_unlock(size, shp->mlock_user);
  	fput(file);
  no_file:
  	security_shm_free(shp);
  	ipc_rcu_putref(shp);
  	return error;
  }
  
  /*
   * Called with shm_ids.rw_mutex and ipcp locked.
   */
  static inline int shm_security(struct kern_ipc_perm *ipcp, int shmflg)
  {
  	struct shmid_kernel *shp;
  
  	shp = container_of(ipcp, struct shmid_kernel, shm_perm);
  	return security_shm_associate(shp, shmflg);
  }
  
  /*
   * Called with shm_ids.rw_mutex and ipcp locked.
   */
  static inline int shm_more_checks(struct kern_ipc_perm *ipcp,
  				struct ipc_params *params)
  {
  	struct shmid_kernel *shp;
  
  	shp = container_of(ipcp, struct shmid_kernel, shm_perm);
  	if (shp->shm_segsz < params->u.size)
  		return -EINVAL;
  
  	return 0;
  }
  
  SYSCALL_DEFINE3(shmget, key_t, key, size_t, size, int, shmflg)
  {
  	struct ipc_namespace *ns;
  	struct ipc_ops shm_ops;
  	struct ipc_params shm_params;
  
  	ns = current->nsproxy->ipc_ns;
  
  	shm_ops.getnew = newseg;
  	shm_ops.associate = shm_security;
  	shm_ops.more_checks = shm_more_checks;
  
  	shm_params.key = key;
  	shm_params.flg = shmflg;
  	shm_params.u.size = size;
  
  	return ipcget(ns, &shm_ids(ns), &shm_ops, &shm_params);
  }
  
  static inline unsigned long copy_shmid_to_user(void __user *buf, struct shmid64_ds *in, int version)
  {
  	switch(version) {
  	case IPC_64:
  		return copy_to_user(buf, in, sizeof(*in));
  	case IPC_OLD:
  	    {
  		struct shmid_ds out;
  
  		memset(&out, 0, sizeof(out));
  		ipc64_perm_to_ipc_perm(&in->shm_perm, &out.shm_perm);
  		out.shm_segsz	= in->shm_segsz;
  		out.shm_atime	= in->shm_atime;
  		out.shm_dtime	= in->shm_dtime;
  		out.shm_ctime	= in->shm_ctime;
  		out.shm_cpid	= in->shm_cpid;
  		out.shm_lpid	= in->shm_lpid;
  		out.shm_nattch	= in->shm_nattch;
  
  		return copy_to_user(buf, &out, sizeof(out));
  	    }
  	default:
  		return -EINVAL;
  	}
  }
  
  static inline unsigned long
  copy_shmid_from_user(struct shmid64_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 shmid_ds tbuf_old;
  
  		if (copy_from_user(&tbuf_old, buf, sizeof(tbuf_old)))
  			return -EFAULT;
  
  		out->shm_perm.uid	= tbuf_old.shm_perm.uid;
  		out->shm_perm.gid	= tbuf_old.shm_perm.gid;
  		out->shm_perm.mode	= tbuf_old.shm_perm.mode;
  
  		return 0;
  	    }
  	default:
  		return -EINVAL;
  	}
  }
  
  static inline unsigned long copy_shminfo_to_user(void __user *buf, struct shminfo64 *in, int version)
  {
  	switch(version) {
  	case IPC_64:
  		return copy_to_user(buf, in, sizeof(*in));
  	case IPC_OLD:
  	    {
  		struct shminfo out;
  
  		if(in->shmmax > INT_MAX)
  			out.shmmax = INT_MAX;
  		else
  			out.shmmax = (int)in->shmmax;
  
  		out.shmmin	= in->shmmin;
  		out.shmmni	= in->shmmni;
  		out.shmseg	= in->shmseg;
  		out.shmall	= in->shmall; 
  
  		return copy_to_user(buf, &out, sizeof(out));
  	    }
  	default:
  		return -EINVAL;
  	}
  }
  
  /*
   * Calculate and add used RSS and swap pages of a shm.
   * Called with shm_ids.rw_mutex held as a reader
   */
  static void shm_add_rss_swap(struct shmid_kernel *shp,
  	unsigned long *rss_add, unsigned long *swp_add)
  {
  	struct inode *inode;
  
  	inode = shp->shm_file->f_path.dentry->d_inode;
  
  	if (is_file_hugepages(shp->shm_file)) {
  		struct address_space *mapping = inode->i_mapping;
  		struct hstate *h = hstate_file(shp->shm_file);
  		*rss_add += pages_per_huge_page(h) * mapping->nrpages;
  	} else {
  #ifdef CONFIG_SHMEM
  		struct shmem_inode_info *info = SHMEM_I(inode);
  		spin_lock(&info->lock);
  		*rss_add += inode->i_mapping->nrpages;
  		*swp_add += info->swapped;
  		spin_unlock(&info->lock);
  #else
  		*rss_add += inode->i_mapping->nrpages;
  #endif
  	}
  }
  
  /*
   * Called with shm_ids.rw_mutex held as a reader
   */
  static void shm_get_stat(struct ipc_namespace *ns, unsigned long *rss,
  		unsigned long *swp)
  {
  	int next_id;
  	int total, in_use;
  
  	*rss = 0;
  	*swp = 0;
  
  	in_use = shm_ids(ns).in_use;
  
  	for (total = 0, next_id = 0; total < in_use; next_id++) {
  		struct kern_ipc_perm *ipc;
  		struct shmid_kernel *shp;
  
  		ipc = idr_find(&shm_ids(ns).ipcs_idr, next_id);
  		if (ipc == NULL)
  			continue;
  		shp = container_of(ipc, struct shmid_kernel, shm_perm);
  
  		shm_add_rss_swap(shp, rss, swp);
  
  		total++;
  	}
  }
  
  /*
   * This function handles some shmctl 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 shmctl_down(struct ipc_namespace *ns, int shmid, int cmd,
  		       struct shmid_ds __user *buf, int version)
  {
  	struct kern_ipc_perm *ipcp;
  	struct shmid64_ds shmid64;
  	struct shmid_kernel *shp;
  	int err;
  
  	if (cmd == IPC_SET) {
  		if (copy_shmid_from_user(&shmid64, buf, version))
  			return -EFAULT;
  	}
  
  	ipcp = ipcctl_pre_down(ns, &shm_ids(ns), shmid, cmd,
  			       &shmid64.shm_perm, 0);
  	if (IS_ERR(ipcp))
  		return PTR_ERR(ipcp);
  
  	shp = container_of(ipcp, struct shmid_kernel, shm_perm);
  
  	err = security_shm_shmctl(shp, cmd);
  	if (err)
  		goto out_unlock;
  	switch (cmd) {
  	case IPC_RMID:
  		do_shm_rmid(ns, ipcp);
  		goto out_up;
  	case IPC_SET:
  		ipc_update_perm(&shmid64.shm_perm, ipcp);
  		shp->shm_ctim = get_seconds();
  		break;
  	default:
  		err = -EINVAL;
  	}
  out_unlock:
  	shm_unlock(shp);
  out_up:
  	up_write(&shm_ids(ns).rw_mutex);
  	return err;
  }
  
  SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
  {
  	struct shmid_kernel *shp;
  	int err, version;
  	struct ipc_namespace *ns;
  
  	if (cmd < 0 || shmid < 0) {
  		err = -EINVAL;
  		goto out;
  	}
  
  	version = ipc_parse_version(&cmd);
  	ns = current->nsproxy->ipc_ns;
  
  	switch (cmd) { /* replace with proc interface ? */
  	case IPC_INFO:
  	{
  		struct shminfo64 shminfo;
  
  		err = security_shm_shmctl(NULL, cmd);
  		if (err)
  			return err;
  
  		memset(&shminfo, 0, sizeof(shminfo));
  		shminfo.shmmni = shminfo.shmseg = ns->shm_ctlmni;
  		shminfo.shmmax = ns->shm_ctlmax;
  		shminfo.shmall = ns->shm_ctlall;
  
  		shminfo.shmmin = SHMMIN;
  		if(copy_shminfo_to_user (buf, &shminfo, version))
  			return -EFAULT;
  
  		down_read(&shm_ids(ns).rw_mutex);
  		err = ipc_get_maxid(&shm_ids(ns));
  		up_read(&shm_ids(ns).rw_mutex);
  
  		if(err<0)
  			err = 0;
  		goto out;
  	}
  	case SHM_INFO:
  	{
  		struct shm_info shm_info;
  
  		err = security_shm_shmctl(NULL, cmd);
  		if (err)
  			return err;
  
  		memset(&shm_info, 0, sizeof(shm_info));
  		down_read(&shm_ids(ns).rw_mutex);
  		shm_info.used_ids = shm_ids(ns).in_use;
  		shm_get_stat (ns, &shm_info.shm_rss, &shm_info.shm_swp);
  		shm_info.shm_tot = ns->shm_tot;
  		shm_info.swap_attempts = 0;
  		shm_info.swap_successes = 0;
  		err = ipc_get_maxid(&shm_ids(ns));
  		up_read(&shm_ids(ns).rw_mutex);
  		if (copy_to_user(buf, &shm_info, sizeof(shm_info))) {
  			err = -EFAULT;
  			goto out;
  		}
  
  		err = err < 0 ? 0 : err;
  		goto out;
  	}
  	case SHM_STAT:
  	case IPC_STAT:
  	{
  		struct shmid64_ds tbuf;
  		int result;
  
  		if (cmd == SHM_STAT) {
  			shp = shm_lock(ns, shmid);
  			if (IS_ERR(shp)) {
  				err = PTR_ERR(shp);
  				goto out;
  			}
  			result = shp->shm_perm.id;
  		} else {
  			shp = shm_lock_check(ns, shmid);
  			if (IS_ERR(shp)) {
  				err = PTR_ERR(shp);
  				goto out;
  			}
  			result = 0;
  		}
  		err = -EACCES;
  		if (ipcperms(ns, &shp->shm_perm, S_IRUGO))
  			goto out_unlock;
  		err = security_shm_shmctl(shp, cmd);
  		if (err)
  			goto out_unlock;
  		memset(&tbuf, 0, sizeof(tbuf));
  		kernel_to_ipc64_perm(&shp->shm_perm, &tbuf.shm_perm);
  		tbuf.shm_segsz	= shp->shm_segsz;
  		tbuf.shm_atime	= shp->shm_atim;
  		tbuf.shm_dtime	= shp->shm_dtim;
  		tbuf.shm_ctime	= shp->shm_ctim;
  		tbuf.shm_cpid	= shp->shm_cprid;
  		tbuf.shm_lpid	= shp->shm_lprid;
  		tbuf.shm_nattch	= shp->shm_nattch;
  		shm_unlock(shp);
  		if(copy_shmid_to_user (buf, &tbuf, version))
  			err = -EFAULT;
  		else
  			err = result;
  		goto out;
  	}
  	case SHM_LOCK:
  	case SHM_UNLOCK:
  	{
  		struct file *shm_file;
  
  		shp = shm_lock_check(ns, shmid);
  		if (IS_ERR(shp)) {
  			err = PTR_ERR(shp);
  			goto out;
  		}
  
  		audit_ipc_obj(&(shp->shm_perm));
  
  		if (!ns_capable(ns->user_ns, CAP_IPC_LOCK)) {
  			uid_t euid = current_euid();
  			err = -EPERM;
  			if (euid != shp->shm_perm.uid &&
  			    euid != shp->shm_perm.cuid)
  				goto out_unlock;
  			if (cmd == SHM_LOCK && !rlimit(RLIMIT_MEMLOCK))
  				goto out_unlock;
  		}
  
  		err = security_shm_shmctl(shp, cmd);
  		if (err)
  			goto out_unlock;
  
  		shm_file = shp->shm_file;
  		if (is_file_hugepages(shm_file))
  			goto out_unlock;
  
  		if (cmd == SHM_LOCK) {
  			struct user_struct *user = current_user();
  			err = shmem_lock(shm_file, 1, user);
  			if (!err && !(shp->shm_perm.mode & SHM_LOCKED)) {
  				shp->shm_perm.mode |= SHM_LOCKED;
  				shp->mlock_user = user;
  			}
  			goto out_unlock;
  		}
  
  		/* SHM_UNLOCK */
  		if (!(shp->shm_perm.mode & SHM_LOCKED))
  			goto out_unlock;
  		shmem_lock(shm_file, 0, shp->mlock_user);
  		shp->shm_perm.mode &= ~SHM_LOCKED;
  		shp->mlock_user = NULL;
  		get_file(shm_file);
  		shm_unlock(shp);
  		shmem_unlock_mapping(shm_file->f_mapping);
  		fput(shm_file);
  		goto out;
  	}
  	case IPC_RMID:
  	case IPC_SET:
  		err = shmctl_down(ns, shmid, cmd, buf, version);
  		return err;
  	default:
  		return -EINVAL;
  	}
  
  out_unlock:
  	shm_unlock(shp);
  out:
  	return err;
  }
  
  /*
   * Fix shmaddr, allocate descriptor, map shm, add attach descriptor to lists.
   *
   * NOTE! Despite the name, this is NOT a direct system call entrypoint. The
   * "raddr" thing points to kernel space, and there has to be a wrapper around
   * this.
   */
  long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
  {
  	struct shmid_kernel *shp;
  	unsigned long addr;
  	unsigned long size;
  	struct file * file;
  	int    err;
  	unsigned long flags;
  	unsigned long prot;
  	int acc_mode;
  	unsigned long user_addr;
  	struct ipc_namespace *ns;
  	struct shm_file_data *sfd;
  	struct path path;
  	fmode_t f_mode;
  
  	err = -EINVAL;
  	if (shmid < 0)
  		goto out;
  	else if ((addr = (ulong)shmaddr)) {
  		if (addr & (SHMLBA-1)) {
  			if (shmflg & SHM_RND)
  				addr &= ~(SHMLBA-1);	   /* round down */
  			else
  #ifndef __ARCH_FORCE_SHMLBA
  				if (addr & ~PAGE_MASK)
  #endif
  					goto out;
  		}
  		flags = MAP_SHARED | MAP_FIXED;
  	} else {
  		if ((shmflg & SHM_REMAP))
  			goto out;
  
  		flags = MAP_SHARED;
  	}
  
  	if (shmflg & SHM_RDONLY) {
  		prot = PROT_READ;
  		acc_mode = S_IRUGO;
  		f_mode = FMODE_READ;
  	} else {
  		prot = PROT_READ | PROT_WRITE;
  		acc_mode = S_IRUGO | S_IWUGO;
  		f_mode = FMODE_READ | FMODE_WRITE;
  	}
  	if (shmflg & SHM_EXEC) {
  		prot |= PROT_EXEC;
  		acc_mode |= S_IXUGO;
  	}
  
  	/*
  	 * We cannot rely on the fs check since SYSV IPC does have an
  	 * additional creator id...
  	 */
  	ns = current->nsproxy->ipc_ns;
  	shp = shm_lock_check(ns, shmid);
  	if (IS_ERR(shp)) {
  		err = PTR_ERR(shp);
  		goto out;
  	}
  
  	err = -EACCES;
  	if (ipcperms(ns, &shp->shm_perm, acc_mode))
  		goto out_unlock;
  
  	err = security_shm_shmat(shp, shmaddr, shmflg);
  	if (err)
  		goto out_unlock;
  
  	path = shp->shm_file->f_path;
  	path_get(&path);
  	shp->shm_nattch++;
  	size = i_size_read(path.dentry->d_inode);
  	shm_unlock(shp);
  
  	err = -ENOMEM;
  	sfd = kzalloc(sizeof(*sfd), GFP_KERNEL);
  	if (!sfd)
  		goto out_put_dentry;
  
  	file = alloc_file(&path, f_mode,
  			  is_file_hugepages(shp->shm_file) ?
  				&shm_file_operations_huge :
  				&shm_file_operations);
  	if (!file)
  		goto out_free;
  
  	file->private_data = sfd;
  	file->f_mapping = shp->shm_file->f_mapping;
  	sfd->id = shp->shm_perm.id;
  	sfd->ns = get_ipc_ns(ns);
  	sfd->file = shp->shm_file;
  	sfd->vm_ops = NULL;
  
  	down_write(&current->mm->mmap_sem);
  	if (addr && !(shmflg & SHM_REMAP)) {
  		err = -EINVAL;
  		if (find_vma_intersection(current->mm, addr, addr + size))
  			goto invalid;
  		/*
  		 * If shm segment goes below stack, make sure there is some
  		 * space left for the stack to grow (at least 4 pages).
  		 */
  		if (addr < current->mm->start_stack &&
  		    addr > current->mm->start_stack - size - PAGE_SIZE * 5)
  			goto invalid;
  	}
  		
  	user_addr = do_mmap (file, addr, size, prot, flags, 0);
  	*raddr = user_addr;
  	err = 0;
  	if (IS_ERR_VALUE(user_addr))
  		err = (long)user_addr;
  invalid:
  	up_write(&current->mm->mmap_sem);
  
  	fput(file);
  
  out_nattch:
  	down_write(&shm_ids(ns).rw_mutex);
  	shp = shm_lock(ns, shmid);
  	BUG_ON(IS_ERR(shp));
  	shp->shm_nattch--;
  	if (shm_may_destroy(ns, shp))
  		shm_destroy(ns, shp);
  	else
  		shm_unlock(shp);
  	up_write(&shm_ids(ns).rw_mutex);
  
  out:
  	return err;
  
  out_unlock:
  	shm_unlock(shp);
  	goto out;
  
  out_free:
  	kfree(sfd);
  out_put_dentry:
  	path_put(&path);
  	goto out_nattch;
  }
  
  SYSCALL_DEFINE3(shmat, int, shmid, char __user *, shmaddr, int, shmflg)
  {
  	unsigned long ret;
  	long err;
  
  	err = do_shmat(shmid, shmaddr, shmflg, &ret);
  	if (err)
  		return err;
  	force_successful_syscall_return();
  	return (long)ret;
  }
  
  /*
   * detach and kill segment if marked destroyed.
   * The work is done in shm_close.
   */
  SYSCALL_DEFINE1(shmdt, char __user *, shmaddr)
  {
  	struct mm_struct *mm = current->mm;
  	struct vm_area_struct *vma;
  	unsigned long addr = (unsigned long)shmaddr;
  	int retval = -EINVAL;
  #ifdef CONFIG_MMU
  	loff_t size = 0;
  	struct vm_area_struct *next;
  #endif
  
  	if (addr & ~PAGE_MASK)
  		return retval;
  
  	down_write(&mm->mmap_sem);
  
  	/*
  	 * This function tries to be smart and unmap shm segments that
  	 * were modified by partial mlock or munmap calls:
  	 * - It first determines the size of the shm segment that should be
  	 *   unmapped: It searches for a vma that is backed by shm and that
  	 *   started at address shmaddr. It records it's size and then unmaps
  	 *   it.
  	 * - Then it unmaps all shm vmas that started at shmaddr and that
  	 *   are within the initially determined size.
  	 * Errors from do_munmap are ignored: the function only fails if
  	 * it's called with invalid parameters or if it's called to unmap
  	 * a part of a vma. Both calls in this function are for full vmas,
  	 * the parameters are directly copied from the vma itself and always
  	 * valid - therefore do_munmap cannot fail. (famous last words?)
  	 */
  	/*
  	 * If it had been mremap()'d, the starting address would not
  	 * match the usual checks anyway. So assume all vma's are
  	 * above the starting address given.
  	 */
  	vma = find_vma(mm, addr);
  
  #ifdef CONFIG_MMU
  	while (vma) {
  		next = vma->vm_next;
  
  		/*
  		 * Check if the starting address would match, i.e. it's
  		 * a fragment created by mprotect() and/or munmap(), or it
  		 * otherwise it starts at this address with no hassles.
  		 */
  		if ((vma->vm_ops == &shm_vm_ops) &&
  			(vma->vm_start - addr)/PAGE_SIZE == vma->vm_pgoff) {
  
  
  			size = vma->vm_file->f_path.dentry->d_inode->i_size;
  			do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start);
  			/*
  			 * We discovered the size of the shm segment, so
  			 * break out of here and fall through to the next
  			 * loop that uses the size information to stop
  			 * searching for matching vma's.
  			 */
  			retval = 0;
  			vma = next;
  			break;
  		}
  		vma = next;
  	}
  
  	/*
  	 * We need look no further than the maximum address a fragment
  	 * could possibly have landed at. Also cast things to loff_t to
  	 * prevent overflows and make comparisons vs. equal-width types.
  	 */
  	size = PAGE_ALIGN(size);
  	while (vma && (loff_t)(vma->vm_end - addr) <= size) {
  		next = vma->vm_next;
  
  		/* finding a matching vma now does not alter retval */
  		if ((vma->vm_ops == &shm_vm_ops) &&
  			(vma->vm_start - addr)/PAGE_SIZE == vma->vm_pgoff)
  
  			do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start);
  		vma = next;
  	}
  
  #else /* CONFIG_MMU */
  	/* under NOMMU conditions, the exact address to be destroyed must be
  	 * given */
  	retval = -EINVAL;
  	if (vma->vm_start == addr && vma->vm_ops == &shm_vm_ops) {
  		do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start);
  		retval = 0;
  	}
  
  #endif
  
  	up_write(&mm->mmap_sem);
  	return retval;
  }
  
  #ifdef CONFIG_PROC_FS
  static int sysvipc_shm_proc_show(struct seq_file *s, void *it)
  {
  	struct shmid_kernel *shp = it;
  	unsigned long rss = 0, swp = 0;
  
  	shm_add_rss_swap(shp, &rss, &swp);
  
  #if BITS_PER_LONG <= 32
  #define SIZE_SPEC "%10lu"
  #else
  #define SIZE_SPEC "%21lu"
  #endif
  
  	return seq_printf(s,
  			  "%10d %10d  %4o " SIZE_SPEC " %5u %5u  "
  			  "%5lu %5u %5u %5u %5u %10lu %10lu %10lu "
  			  SIZE_SPEC " " SIZE_SPEC "\n",
  			  shp->shm_perm.key,
  			  shp->shm_perm.id,
  			  shp->shm_perm.mode,
  			  shp->shm_segsz,
  			  shp->shm_cprid,
  			  shp->shm_lprid,
  			  shp->shm_nattch,
  			  shp->shm_perm.uid,
  			  shp->shm_perm.gid,
  			  shp->shm_perm.cuid,
  			  shp->shm_perm.cgid,
  			  shp->shm_atim,
  			  shp->shm_dtim,
  			  shp->shm_ctim,
  			  rss * PAGE_SIZE,
  			  swp * PAGE_SIZE);
  }
  #endif
  