Linux 3.16-rc2

[linux/fpc-iii.git] / ipc / shm.c

/*
 * 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>
 *
 * Better ipc lock (kern_ipc_perm.lock) handling
 * Davidlohr Bueso <davidlohr.bueso@hp.com>, June 2013.
 */

#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 <linux/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.rwsem (writer) and the shp structure locked.
 * Only shm_ids.rwsem 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);
}

static inline struct shmid_kernel *shm_obtain_object(struct ipc_namespace *ns, int id)
{
        struct kern_ipc_perm *ipcp = ipc_obtain_object(&shm_ids(ns), id);

        if (IS_ERR(ipcp))
                return ERR_CAST(ipcp);

        return container_of(ipcp, struct shmid_kernel, shm_perm);
}

static inline struct shmid_kernel *shm_obtain_object_check(struct ipc_namespace *ns, int id)
{
        struct kern_ipc_perm *ipcp = ipc_obtain_object_check(&shm_ids(ns), id);

        if (IS_ERR(ipcp))
                return ERR_CAST(ipcp);

        return container_of(ipcp, struct shmid_kernel, shm_perm);
}

/*
 * shm_lock_(check_) routines are called in the paths where the rwsem
 * 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();
        ipc_lock_object(&ipcp->shm_perm);
}

static void shm_rcu_free(struct rcu_head *head)
{
        struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu);
        struct shmid_kernel *shp = ipc_rcu_to_struct(p);

        security_shm_free(shp);
        ipc_rcu_free(head);
}

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.rwsem (writer) locked,
 * but returns with shp unlocked and freed.
 */
static void shm_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp)
{
        struct file *shm_file;

        shm_file = shp->shm_file;
        shp->shm_file = NULL;
        ns->shm_tot -= (shp->shm_segsz + PAGE_SIZE - 1) >> PAGE_SHIFT;
        shm_rmid(ns, shp);
        shm_unlock(shp);
        if (!is_file_hugepages(shm_file))
                shmem_lock(shm_file, 0, shp->mlock_user);
        else if (shp->mlock_user)
                user_shm_unlock(file_inode(shm_file)->i_size, shp->mlock_user);
        fput(shm_file);
        ipc_rcu_putref(shp, shm_rcu_free);
}

/*
 * 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).rwsem);
        /* 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).rwsem);
}

/* Called with ns->shm_ids(ns).rwsem 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).rwsem 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 rwsem, 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).rwsem);
        if (shm_ids(ns).in_use)
                idr_for_each(&shm_ids(ns).ipcs_idr, &shm_try_destroy_orphaned, ns);
        up_write(&shm_ids(ns).rwsem);
}


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).rwsem);
        if (shm_ids(ns).in_use)
                idr_for_each(&shm_ids(ns).ipcs_idr, &shm_try_destroy_current, ns);
        up_write(&shm_ids(ns).rwsem);
}

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 long shm_fallocate(struct file *file, int mode, loff_t offset,
                          loff_t len)
{
        struct shm_file_data *sfd = shm_file_data(file);

        if (!sfd->file->f_op->fallocate)
                return -EOPNOTSUPP;
        return sfd->file->f_op->fallocate(file, mode, offset, len);
}

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,
        .fallocate      = shm_fallocate,
};

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,
        .fallocate      = shm_fallocate,
};

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.rwsem 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;
        size_t 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 (numpages << PAGE_SHIFT < size)
                return -ENOSPC;

        if (ns->shm_tot + numpages < ns->shm_tot ||
                        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, ipc_rcu_free);
                return error;
        }

        sprintf(name, "SYSV%08x", key);
        if (shmflg & SHM_HUGETLB) {
                struct hstate *hs;
                size_t hugesize;

                hs = hstate_sizelog((shmflg >> SHM_HUGE_SHIFT) & SHM_HUGE_MASK);
                if (!hs) {
                        error = -EINVAL;
                        goto no_file;
                }
                hugesize = ALIGN(size, huge_page_size(hs));

                /* hugetlb_file_setup applies strict accounting */
                if (shmflg & SHM_NORESERVE)
                        acctflag = VM_NORESERVE;
                file = hugetlb_file_setup(name, hugesize, acctflag,
                                  &shp->mlock_user, HUGETLB_SHMFS_INODE,
                                (shmflg >> SHM_HUGE_SHIFT) & SHM_HUGE_MASK);
        } 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_inode(file)->i_ino = shp->shm_perm.id;

        ns->shm_tot += numpages;
        error = shp->shm_perm.id;

        ipc_unlock_object(&shp->shm_perm);
        rcu_read_unlock();
        return error;

no_id:
        if (is_file_hugepages(file) && shp->mlock_user)
                user_shm_unlock(size, shp->mlock_user);
        fput(file);
no_file:
        ipc_rcu_putref(shp, shm_rcu_free);
        return error;
}

/*
 * Called with shm_ids.rwsem 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.rwsem 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;
        static const struct ipc_ops shm_ops = {
                .getnew = newseg,
                .associate = shm_security,
                .more_checks = shm_more_checks,
        };
        struct ipc_params shm_params;

        ns = current->nsproxy->ipc_ns;

        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.rwsem 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 = file_inode(shp->shm_file);

        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.rwsem 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 rwsem
 * to be held in write mode.
 * NOTE: no locks must be held, the rwsem 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;
        }

        down_write(&shm_ids(ns).rwsem);
        rcu_read_lock();

        ipcp = ipcctl_pre_down_nolock(ns, &shm_ids(ns), shmid, cmd,
                                      &shmid64.shm_perm, 0);
        if (IS_ERR(ipcp)) {
                err = PTR_ERR(ipcp);
                goto out_unlock1;
        }

        shp = container_of(ipcp, struct shmid_kernel, shm_perm);

        err = security_shm_shmctl(shp, cmd);
        if (err)
                goto out_unlock1;

        switch (cmd) {
        case IPC_RMID:
                ipc_lock_object(&shp->shm_perm);
                /* do_shm_rmid unlocks the ipc object and rcu */
                do_shm_rmid(ns, ipcp);
                goto out_up;
        case IPC_SET:
                ipc_lock_object(&shp->shm_perm);
                err = ipc_update_perm(&shmid64.shm_perm, ipcp);
                if (err)
                        goto out_unlock0;
                shp->shm_ctim = get_seconds();
                break;
        default:
                err = -EINVAL;
                goto out_unlock1;
        }

out_unlock0:
        ipc_unlock_object(&shp->shm_perm);
out_unlock1:
        rcu_read_unlock();
out_up:
        up_write(&shm_ids(ns).rwsem);
        return err;
}

static int shmctl_nolock(struct ipc_namespace *ns, int shmid,
                         int cmd, int version, void __user *buf)
{
        int err;
        struct shmid_kernel *shp;

        /* preliminary security checks for *_INFO */
        if (cmd == IPC_INFO || cmd == SHM_INFO) {
                err = security_shm_shmctl(NULL, cmd);
                if (err)
                        return err;
        }

        switch (cmd) {
        case IPC_INFO:
        {
                struct shminfo64 shminfo;

                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).rwsem);
                err = ipc_get_maxid(&shm_ids(ns));
                up_read(&shm_ids(ns).rwsem);

                if (err < 0)
                        err = 0;
                goto out;
        }
        case SHM_INFO:
        {
                struct shm_info shm_info;

                memset(&shm_info, 0, sizeof(shm_info));
                down_read(&shm_ids(ns).rwsem);
                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).rwsem);
                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;

                rcu_read_lock();
                if (cmd == SHM_STAT) {
                        shp = shm_obtain_object(ns, shmid);
                        if (IS_ERR(shp)) {
                                err = PTR_ERR(shp);
                                goto out_unlock;
                        }
                        result = shp->shm_perm.id;
                } else {
                        shp = shm_obtain_object_check(ns, shmid);
                        if (IS_ERR(shp)) {
                                err = PTR_ERR(shp);
                                goto out_unlock;
                        }
                        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;
                rcu_read_unlock();

                if (copy_shmid_to_user(buf, &tbuf, version))
                        err = -EFAULT;
                else
                        err = result;
                goto out;
        }
        default:
                return -EINVAL;
        }

out_unlock:
        rcu_read_unlock();
out:
        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)
                return -EINVAL;

        version = ipc_parse_version(&cmd);
        ns = current->nsproxy->ipc_ns;

        switch (cmd) {
        case IPC_INFO:
        case SHM_INFO:
        case SHM_STAT:
        case IPC_STAT:
                return shmctl_nolock(ns, shmid, cmd, version, buf);
        case IPC_RMID:
        case IPC_SET:
                return shmctl_down(ns, shmid, cmd, buf, version);
        case SHM_LOCK:
        case SHM_UNLOCK:
        {
                struct file *shm_file;

                rcu_read_lock();
                shp = shm_obtain_object_check(ns, shmid);
                if (IS_ERR(shp)) {
                        err = PTR_ERR(shp);
                        goto out_unlock1;
                }

                audit_ipc_obj(&(shp->shm_perm));
                err = security_shm_shmctl(shp, cmd);
                if (err)
                        goto out_unlock1;

                ipc_lock_object(&shp->shm_perm);

                /* check if shm_destroy() is tearing down shp */
                if (!ipc_valid_object(&shp->shm_perm)) {
                        err = -EIDRM;
                        goto out_unlock0;
                }

                if (!ns_capable(ns->user_ns, CAP_IPC_LOCK)) {
                        kuid_t euid = current_euid();
                        if (!uid_eq(euid, shp->shm_perm.uid) &&
                            !uid_eq(euid, shp->shm_perm.cuid)) {
                                err = -EPERM;
                                goto out_unlock0;
                        }
                        if (cmd == SHM_LOCK && !rlimit(RLIMIT_MEMLOCK)) {
                                err = -EPERM;
                                goto out_unlock0;
                        }
                }

                shm_file = shp->shm_file;
                if (is_file_hugepages(shm_file))
                        goto out_unlock0;

                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_unlock0;
                }

                /* SHM_UNLOCK */
                if (!(shp->shm_perm.mode & SHM_LOCKED))
                        goto out_unlock0;
                shmem_lock(shm_file, 0, shp->mlock_user);
                shp->shm_perm.mode &= ~SHM_LOCKED;
                shp->mlock_user = NULL;
                get_file(shm_file);
                ipc_unlock_object(&shp->shm_perm);
                rcu_read_unlock();
                shmem_unlock_mapping(shm_file->f_mapping);

                fput(shm_file);
                return err;
        }
        default:
                return -EINVAL;
        }

out_unlock0:
        ipc_unlock_object(&shp->shm_perm);
out_unlock1:
        rcu_read_unlock();
        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,
              unsigned long shmlba)
{
        struct shmid_kernel *shp;
        unsigned long addr;
        unsigned long size;
        struct file *file;
        int    err;
        unsigned long flags;
        unsigned long prot;
        int acc_mode;
        struct ipc_namespace *ns;
        struct shm_file_data *sfd;
        struct path path;
        fmode_t f_mode;
        unsigned long populate = 0;

        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;
        rcu_read_lock();
        shp = shm_obtain_object_check(ns, shmid);
        if (IS_ERR(shp)) {
                err = PTR_ERR(shp);
                goto out_unlock;
        }

        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;

        ipc_lock_object(&shp->shm_perm);

        /* check if shm_destroy() is tearing down shp */
        if (!ipc_valid_object(&shp->shm_perm)) {
                ipc_unlock_object(&shp->shm_perm);
                err = -EIDRM;
                goto out_unlock;
        }

        path = shp->shm_file->f_path;
        path_get(&path);
        shp->shm_nattch++;
        size = i_size_read(path.dentry->d_inode);
        ipc_unlock_object(&shp->shm_perm);
        rcu_read_unlock();

        err = -ENOMEM;
        sfd = kzalloc(sizeof(*sfd), GFP_KERNEL);
        if (!sfd) {
                path_put(&path);
                goto out_nattch;
        }

        file = alloc_file(&path, f_mode,
                          is_file_hugepages(shp->shm_file) ?
                                &shm_file_operations_huge :
                                &shm_file_operations);
        err = PTR_ERR(file);
        if (IS_ERR(file)) {
                kfree(sfd);
                path_put(&path);
                goto out_nattch;
        }

        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;

        err = security_mmap_file(file, prot, flags);
        if (err)
                goto out_fput;

        down_write(&current->mm->mmap_sem);
        if (addr && !(shmflg & SHM_REMAP)) {
                err = -EINVAL;
                if (addr + size < addr)
                        goto invalid;

                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;
        }

        addr = do_mmap_pgoff(file, addr, size, prot, flags, 0, &populate);
        *raddr = addr;
        err = 0;
        if (IS_ERR_VALUE(addr))
                err = (long)addr;
invalid:
        up_write(&current->mm->mmap_sem);
        if (populate)
                mm_populate(addr, populate);

out_fput:
        fput(file);

out_nattch:
        down_write(&shm_ids(ns).rwsem);
        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).rwsem);
        return err;

out_unlock:
        rcu_read_unlock();
out:
        return err;
}

SYSCALL_DEFINE3(shmat, int, shmid, char __user *, shmaddr, int, shmflg)
{
        unsigned long ret;
        long err;

        err = do_shmat(shmid, shmaddr, shmflg, &ret, SHMLBA);
        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 = file_inode(vma->vm_file)->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 */
        if (vma && 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 user_namespace *user_ns = seq_user_ns(s);
        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,
                          from_kuid_munged(user_ns, shp->shm_perm.uid),
                          from_kgid_munged(user_ns, shp->shm_perm.gid),
                          from_kuid_munged(user_ns, shp->shm_perm.cuid),
                          from_kgid_munged(user_ns, shp->shm_perm.cgid),
                          shp->shm_atim,
                          shp->shm_dtim,
                          shp->shm_ctim,
                          rss * PAGE_SIZE,
                          swp * PAGE_SIZE);
}
#endif