kselftest/cgroup: fix variable dereferenced before check warning

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

/*
 * POSIX message queues filesystem for Linux.
 *
 * Copyright (C) 2003,2004  Krzysztof Benedyczak    (golbi@mat.uni.torun.pl)
 *                          Michal Wronski          (michal.wronski@gmail.com)
 *
 * Spinlocks:               Mohamed Abbas           (abbas.mohamed@intel.com)
 * Lockless receive & send, fd based notify:
 *                          Manfred Spraul          (manfred@colorfullife.com)
 *
 * Audit:                   George Wilson           (ltcgcw@us.ibm.com)
 *
 * This file is released under the GPL.
 */

#include <linux/capability.h>
#include <linux/init.h>
#include <linux/pagemap.h>
#include <linux/file.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/sysctl.h>
#include <linux/poll.h>
#include <linux/mqueue.h>
#include <linux/msg.h>
#include <linux/skbuff.h>
#include <linux/vmalloc.h>
#include <linux/netlink.h>
#include <linux/syscalls.h>
#include <linux/audit.h>
#include <linux/signal.h>
#include <linux/mutex.h>
#include <linux/nsproxy.h>
#include <linux/pid.h>
#include <linux/ipc_namespace.h>
#include <linux/user_namespace.h>
#include <linux/slab.h>
#include <linux/sched/wake_q.h>
#include <linux/sched/signal.h>
#include <linux/sched/user.h>

#include <net/sock.h>
#include "util.h"

#define MQUEUE_MAGIC    0x19800202
#define DIRENT_SIZE     20
#define FILENT_SIZE     80

#define SEND            0
#define RECV            1

#define STATE_NONE      0
#define STATE_READY     1

struct posix_msg_tree_node {
        struct rb_node          rb_node;
        struct list_head        msg_list;
        int                     priority;
};

struct ext_wait_queue {         /* queue of sleeping tasks */
        struct task_struct *task;
        struct list_head list;
        struct msg_msg *msg;    /* ptr of loaded message */
        int state;              /* one of STATE_* values */
};

struct mqueue_inode_info {
        spinlock_t lock;
        struct inode vfs_inode;
        wait_queue_head_t wait_q;

        struct rb_root msg_tree;
        struct posix_msg_tree_node *node_cache;
        struct mq_attr attr;

        struct sigevent notify;
        struct pid *notify_owner;
        struct user_namespace *notify_user_ns;
        struct user_struct *user;       /* user who created, for accounting */
        struct sock *notify_sock;
        struct sk_buff *notify_cookie;

        /* for tasks waiting for free space and messages, respectively */
        struct ext_wait_queue e_wait_q[2];

        unsigned long qsize; /* size of queue in memory (sum of all msgs) */
};

static const struct inode_operations mqueue_dir_inode_operations;
static const struct file_operations mqueue_file_operations;
static const struct super_operations mqueue_super_ops;
static void remove_notification(struct mqueue_inode_info *info);

static struct kmem_cache *mqueue_inode_cachep;

static struct ctl_table_header *mq_sysctl_table;

static inline struct mqueue_inode_info *MQUEUE_I(struct inode *inode)
{
        return container_of(inode, struct mqueue_inode_info, vfs_inode);
}

/*
 * This routine should be called with the mq_lock held.
 */
static inline struct ipc_namespace *__get_ns_from_inode(struct inode *inode)
{
        return get_ipc_ns(inode->i_sb->s_fs_info);
}

static struct ipc_namespace *get_ns_from_inode(struct inode *inode)
{
        struct ipc_namespace *ns;

        spin_lock(&mq_lock);
        ns = __get_ns_from_inode(inode);
        spin_unlock(&mq_lock);
        return ns;
}

/* Auxiliary functions to manipulate messages' list */
static int msg_insert(struct msg_msg *msg, struct mqueue_inode_info *info)
{
        struct rb_node **p, *parent = NULL;
        struct posix_msg_tree_node *leaf;

        p = &info->msg_tree.rb_node;
        while (*p) {
                parent = *p;
                leaf = rb_entry(parent, struct posix_msg_tree_node, rb_node);

                if (likely(leaf->priority == msg->m_type))
                        goto insert_msg;
                else if (msg->m_type < leaf->priority)
                        p = &(*p)->rb_left;
                else
                        p = &(*p)->rb_right;
        }
        if (info->node_cache) {
                leaf = info->node_cache;
                info->node_cache = NULL;
        } else {
                leaf = kmalloc(sizeof(*leaf), GFP_ATOMIC);
                if (!leaf)
                        return -ENOMEM;
                INIT_LIST_HEAD(&leaf->msg_list);
        }
        leaf->priority = msg->m_type;
        rb_link_node(&leaf->rb_node, parent, p);
        rb_insert_color(&leaf->rb_node, &info->msg_tree);
insert_msg:
        info->attr.mq_curmsgs++;
        info->qsize += msg->m_ts;
        list_add_tail(&msg->m_list, &leaf->msg_list);
        return 0;
}

static inline struct msg_msg *msg_get(struct mqueue_inode_info *info)
{
        struct rb_node **p, *parent = NULL;
        struct posix_msg_tree_node *leaf;
        struct msg_msg *msg;

try_again:
        p = &info->msg_tree.rb_node;
        while (*p) {
                parent = *p;
                /*
                 * During insert, low priorities go to the left and high to the
                 * right.  On receive, we want the highest priorities first, so
                 * walk all the way to the right.
                 */
                p = &(*p)->rb_right;
        }
        if (!parent) {
                if (info->attr.mq_curmsgs) {
                        pr_warn_once("Inconsistency in POSIX message queue, "
                                     "no tree element, but supposedly messages "
                                     "should exist!\n");
                        info->attr.mq_curmsgs = 0;
                }
                return NULL;
        }
        leaf = rb_entry(parent, struct posix_msg_tree_node, rb_node);
        if (unlikely(list_empty(&leaf->msg_list))) {
                pr_warn_once("Inconsistency in POSIX message queue, "
                             "empty leaf node but we haven't implemented "
                             "lazy leaf delete!\n");
                rb_erase(&leaf->rb_node, &info->msg_tree);
                if (info->node_cache) {
                        kfree(leaf);
                } else {
                        info->node_cache = leaf;
                }
                goto try_again;
        } else {
                msg = list_first_entry(&leaf->msg_list,
                                       struct msg_msg, m_list);
                list_del(&msg->m_list);
                if (list_empty(&leaf->msg_list)) {
                        rb_erase(&leaf->rb_node, &info->msg_tree);
                        if (info->node_cache) {
                                kfree(leaf);
                        } else {
                                info->node_cache = leaf;
                        }
                }
        }
        info->attr.mq_curmsgs--;
        info->qsize -= msg->m_ts;
        return msg;
}

static struct inode *mqueue_get_inode(struct super_block *sb,
                struct ipc_namespace *ipc_ns, umode_t mode,
                struct mq_attr *attr)
{
        struct user_struct *u = current_user();
        struct inode *inode;
        int ret = -ENOMEM;

        inode = new_inode(sb);
        if (!inode)
                goto err;

        inode->i_ino = get_next_ino();
        inode->i_mode = mode;
        inode->i_uid = current_fsuid();
        inode->i_gid = current_fsgid();
        inode->i_mtime = inode->i_ctime = inode->i_atime = current_time(inode);

        if (S_ISREG(mode)) {
                struct mqueue_inode_info *info;
                unsigned long mq_bytes, mq_treesize;

                inode->i_fop = &mqueue_file_operations;
                inode->i_size = FILENT_SIZE;
                /* mqueue specific info */
                info = MQUEUE_I(inode);
                spin_lock_init(&info->lock);
                init_waitqueue_head(&info->wait_q);
                INIT_LIST_HEAD(&info->e_wait_q[0].list);
                INIT_LIST_HEAD(&info->e_wait_q[1].list);
                info->notify_owner = NULL;
                info->notify_user_ns = NULL;
                info->qsize = 0;
                info->user = NULL;      /* set when all is ok */
                info->msg_tree = RB_ROOT;
                info->node_cache = NULL;
                memset(&info->attr, 0, sizeof(info->attr));
                info->attr.mq_maxmsg = min(ipc_ns->mq_msg_max,
                                           ipc_ns->mq_msg_default);
                info->attr.mq_msgsize = min(ipc_ns->mq_msgsize_max,
                                            ipc_ns->mq_msgsize_default);
                if (attr) {
                        info->attr.mq_maxmsg = attr->mq_maxmsg;
                        info->attr.mq_msgsize = attr->mq_msgsize;
                }
                /*
                 * We used to allocate a static array of pointers and account
                 * the size of that array as well as one msg_msg struct per
                 * possible message into the queue size. That's no longer
                 * accurate as the queue is now an rbtree and will grow and
                 * shrink depending on usage patterns.  We can, however, still
                 * account one msg_msg struct per message, but the nodes are
                 * allocated depending on priority usage, and most programs
                 * only use one, or a handful, of priorities.  However, since
                 * this is pinned memory, we need to assume worst case, so
                 * that means the min(mq_maxmsg, max_priorities) * struct
                 * posix_msg_tree_node.
                 */

                ret = -EINVAL;
                if (info->attr.mq_maxmsg <= 0 || info->attr.mq_msgsize <= 0)
                        goto out_inode;
                if (capable(CAP_SYS_RESOURCE)) {
                        if (info->attr.mq_maxmsg > HARD_MSGMAX ||
                            info->attr.mq_msgsize > HARD_MSGSIZEMAX)
                                goto out_inode;
                } else {
                        if (info->attr.mq_maxmsg > ipc_ns->mq_msg_max ||
                                        info->attr.mq_msgsize > ipc_ns->mq_msgsize_max)
                                goto out_inode;
                }
                ret = -EOVERFLOW;
                /* check for overflow */
                if (info->attr.mq_msgsize > ULONG_MAX/info->attr.mq_maxmsg)
                        goto out_inode;
                mq_treesize = info->attr.mq_maxmsg * sizeof(struct msg_msg) +
                        min_t(unsigned int, info->attr.mq_maxmsg, MQ_PRIO_MAX) *
                        sizeof(struct posix_msg_tree_node);
                mq_bytes = info->attr.mq_maxmsg * info->attr.mq_msgsize;
                if (mq_bytes + mq_treesize < mq_bytes)
                        goto out_inode;
                mq_bytes += mq_treesize;
                spin_lock(&mq_lock);
                if (u->mq_bytes + mq_bytes < u->mq_bytes ||
                    u->mq_bytes + mq_bytes > rlimit(RLIMIT_MSGQUEUE)) {
                        spin_unlock(&mq_lock);
                        /* mqueue_evict_inode() releases info->messages */
                        ret = -EMFILE;
                        goto out_inode;
                }
                u->mq_bytes += mq_bytes;
                spin_unlock(&mq_lock);

                /* all is ok */
                info->user = get_uid(u);
        } else if (S_ISDIR(mode)) {
                inc_nlink(inode);
                /* Some things misbehave if size == 0 on a directory */
                inode->i_size = 2 * DIRENT_SIZE;
                inode->i_op = &mqueue_dir_inode_operations;
                inode->i_fop = &simple_dir_operations;
        }

        return inode;
out_inode:
        iput(inode);
err:
        return ERR_PTR(ret);
}

static int mqueue_fill_super(struct super_block *sb, void *data, int silent)
{
        struct inode *inode;
        struct ipc_namespace *ns = sb->s_fs_info;

        sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
        sb->s_blocksize = PAGE_SIZE;
        sb->s_blocksize_bits = PAGE_SHIFT;
        sb->s_magic = MQUEUE_MAGIC;
        sb->s_op = &mqueue_super_ops;

        inode = mqueue_get_inode(sb, ns, S_IFDIR | S_ISVTX | S_IRWXUGO, NULL);
        if (IS_ERR(inode))
                return PTR_ERR(inode);

        sb->s_root = d_make_root(inode);
        if (!sb->s_root)
                return -ENOMEM;
        return 0;
}

static struct dentry *mqueue_mount(struct file_system_type *fs_type,
                         int flags, const char *dev_name,
                         void *data)
{
        struct ipc_namespace *ns;
        if (flags & SB_KERNMOUNT) {
                ns = data;
                data = NULL;
        } else {
                ns = current->nsproxy->ipc_ns;
        }
        return mount_ns(fs_type, flags, data, ns, ns->user_ns, mqueue_fill_super);
}

static void init_once(void *foo)
{
        struct mqueue_inode_info *p = (struct mqueue_inode_info *) foo;

        inode_init_once(&p->vfs_inode);
}

static struct inode *mqueue_alloc_inode(struct super_block *sb)
{
        struct mqueue_inode_info *ei;

        ei = kmem_cache_alloc(mqueue_inode_cachep, GFP_KERNEL);
        if (!ei)
                return NULL;
        return &ei->vfs_inode;
}

static void mqueue_i_callback(struct rcu_head *head)
{
        struct inode *inode = container_of(head, struct inode, i_rcu);
        kmem_cache_free(mqueue_inode_cachep, MQUEUE_I(inode));
}

static void mqueue_destroy_inode(struct inode *inode)
{
        call_rcu(&inode->i_rcu, mqueue_i_callback);
}

static void mqueue_evict_inode(struct inode *inode)
{
        struct mqueue_inode_info *info;
        struct user_struct *user;
        unsigned long mq_bytes, mq_treesize;
        struct ipc_namespace *ipc_ns;
        struct msg_msg *msg;

        clear_inode(inode);

        if (S_ISDIR(inode->i_mode))
                return;

        ipc_ns = get_ns_from_inode(inode);
        info = MQUEUE_I(inode);
        spin_lock(&info->lock);
        while ((msg = msg_get(info)) != NULL)
                free_msg(msg);
        kfree(info->node_cache);
        spin_unlock(&info->lock);

        /* Total amount of bytes accounted for the mqueue */
        mq_treesize = info->attr.mq_maxmsg * sizeof(struct msg_msg) +
                min_t(unsigned int, info->attr.mq_maxmsg, MQ_PRIO_MAX) *
                sizeof(struct posix_msg_tree_node);

        mq_bytes = mq_treesize + (info->attr.mq_maxmsg *
                                  info->attr.mq_msgsize);

        user = info->user;
        if (user) {
                spin_lock(&mq_lock);
                user->mq_bytes -= mq_bytes;
                /*
                 * get_ns_from_inode() ensures that the
                 * (ipc_ns = sb->s_fs_info) is either a valid ipc_ns
                 * to which we now hold a reference, or it is NULL.
                 * We can't put it here under mq_lock, though.
                 */
                if (ipc_ns)
                        ipc_ns->mq_queues_count--;
                spin_unlock(&mq_lock);
                free_uid(user);
        }
        if (ipc_ns)
                put_ipc_ns(ipc_ns);
}

static int mqueue_create_attr(struct dentry *dentry, umode_t mode, void *arg)
{
        struct inode *dir = dentry->d_parent->d_inode;
        struct inode *inode;
        struct mq_attr *attr = arg;
        int error;
        struct ipc_namespace *ipc_ns;

        spin_lock(&mq_lock);
        ipc_ns = __get_ns_from_inode(dir);
        if (!ipc_ns) {
                error = -EACCES;
                goto out_unlock;
        }

        if (ipc_ns->mq_queues_count >= ipc_ns->mq_queues_max &&
            !capable(CAP_SYS_RESOURCE)) {
                error = -ENOSPC;
                goto out_unlock;
        }
        ipc_ns->mq_queues_count++;
        spin_unlock(&mq_lock);

        inode = mqueue_get_inode(dir->i_sb, ipc_ns, mode, attr);
        if (IS_ERR(inode)) {
                error = PTR_ERR(inode);
                spin_lock(&mq_lock);
                ipc_ns->mq_queues_count--;
                goto out_unlock;
        }

        put_ipc_ns(ipc_ns);
        dir->i_size += DIRENT_SIZE;
        dir->i_ctime = dir->i_mtime = dir->i_atime = current_time(dir);

        d_instantiate(dentry, inode);
        dget(dentry);
        return 0;
out_unlock:
        spin_unlock(&mq_lock);
        if (ipc_ns)
                put_ipc_ns(ipc_ns);
        return error;
}

static int mqueue_create(struct inode *dir, struct dentry *dentry,
                                umode_t mode, bool excl)
{
        return mqueue_create_attr(dentry, mode, NULL);
}

static int mqueue_unlink(struct inode *dir, struct dentry *dentry)
{
        struct inode *inode = d_inode(dentry);

        dir->i_ctime = dir->i_mtime = dir->i_atime = current_time(dir);
        dir->i_size -= DIRENT_SIZE;
        drop_nlink(inode);
        dput(dentry);
        return 0;
}

/*
*       This is routine for system read from queue file.
*       To avoid mess with doing here some sort of mq_receive we allow
*       to read only queue size & notification info (the only values
*       that are interesting from user point of view and aren't accessible
*       through std routines)
*/
static ssize_t mqueue_read_file(struct file *filp, char __user *u_data,
                                size_t count, loff_t *off)
{
        struct mqueue_inode_info *info = MQUEUE_I(file_inode(filp));
        char buffer[FILENT_SIZE];
        ssize_t ret;

        spin_lock(&info->lock);
        snprintf(buffer, sizeof(buffer),
                        "QSIZE:%-10lu NOTIFY:%-5d SIGNO:%-5d NOTIFY_PID:%-6d\n",
                        info->qsize,
                        info->notify_owner ? info->notify.sigev_notify : 0,
                        (info->notify_owner &&
                         info->notify.sigev_notify == SIGEV_SIGNAL) ?
                                info->notify.sigev_signo : 0,
                        pid_vnr(info->notify_owner));
        spin_unlock(&info->lock);
        buffer[sizeof(buffer)-1] = '\0';

        ret = simple_read_from_buffer(u_data, count, off, buffer,
                                strlen(buffer));
        if (ret <= 0)
                return ret;

        file_inode(filp)->i_atime = file_inode(filp)->i_ctime = current_time(file_inode(filp));
        return ret;
}

static int mqueue_flush_file(struct file *filp, fl_owner_t id)
{
        struct mqueue_inode_info *info = MQUEUE_I(file_inode(filp));

        spin_lock(&info->lock);
        if (task_tgid(current) == info->notify_owner)
                remove_notification(info);

        spin_unlock(&info->lock);
        return 0;
}

static __poll_t mqueue_poll_file(struct file *filp, struct poll_table_struct *poll_tab)
{
        struct mqueue_inode_info *info = MQUEUE_I(file_inode(filp));
        __poll_t retval = 0;

        poll_wait(filp, &info->wait_q, poll_tab);

        spin_lock(&info->lock);
        if (info->attr.mq_curmsgs)
                retval = EPOLLIN | EPOLLRDNORM;

        if (info->attr.mq_curmsgs < info->attr.mq_maxmsg)
                retval |= EPOLLOUT | EPOLLWRNORM;
        spin_unlock(&info->lock);

        return retval;
}

/* Adds current to info->e_wait_q[sr] before element with smaller prio */
static void wq_add(struct mqueue_inode_info *info, int sr,
                        struct ext_wait_queue *ewp)
{
        struct ext_wait_queue *walk;

        ewp->task = current;

        list_for_each_entry(walk, &info->e_wait_q[sr].list, list) {
                if (walk->task->prio <= current->prio) {
                        list_add_tail(&ewp->list, &walk->list);
                        return;
                }
        }
        list_add_tail(&ewp->list, &info->e_wait_q[sr].list);
}

/*
 * Puts current task to sleep. Caller must hold queue lock. After return
 * lock isn't held.
 * sr: SEND or RECV
 */
static int wq_sleep(struct mqueue_inode_info *info, int sr,
                    ktime_t *timeout, struct ext_wait_queue *ewp)
        __releases(&info->lock)
{
        int retval;
        signed long time;

        wq_add(info, sr, ewp);

        for (;;) {
                __set_current_state(TASK_INTERRUPTIBLE);

                spin_unlock(&info->lock);
                time = schedule_hrtimeout_range_clock(timeout, 0,
                        HRTIMER_MODE_ABS, CLOCK_REALTIME);

                if (ewp->state == STATE_READY) {
                        retval = 0;
                        goto out;
                }
                spin_lock(&info->lock);
                if (ewp->state == STATE_READY) {
                        retval = 0;
                        goto out_unlock;
                }
                if (signal_pending(current)) {
                        retval = -ERESTARTSYS;
                        break;
                }
                if (time == 0) {
                        retval = -ETIMEDOUT;
                        break;
                }
        }
        list_del(&ewp->list);
out_unlock:
        spin_unlock(&info->lock);
out:
        return retval;
}

/*
 * Returns waiting task that should be serviced first or NULL if none exists
 */
static struct ext_wait_queue *wq_get_first_waiter(
                struct mqueue_inode_info *info, int sr)
{
        struct list_head *ptr;

        ptr = info->e_wait_q[sr].list.prev;
        if (ptr == &info->e_wait_q[sr].list)
                return NULL;
        return list_entry(ptr, struct ext_wait_queue, list);
}


static inline void set_cookie(struct sk_buff *skb, char code)
{
        ((char *)skb->data)[NOTIFY_COOKIE_LEN-1] = code;
}

/*
 * The next function is only to split too long sys_mq_timedsend
 */
static void __do_notify(struct mqueue_inode_info *info)
{
        /* notification
         * invoked when there is registered process and there isn't process
         * waiting synchronously for message AND state of queue changed from
         * empty to not empty. Here we are sure that no one is waiting
         * synchronously. */
        if (info->notify_owner &&
            info->attr.mq_curmsgs == 1) {
                struct siginfo sig_i;
                switch (info->notify.sigev_notify) {
                case SIGEV_NONE:
                        break;
                case SIGEV_SIGNAL:
                        /* sends signal */

                        clear_siginfo(&sig_i);
                        sig_i.si_signo = info->notify.sigev_signo;
                        sig_i.si_errno = 0;
                        sig_i.si_code = SI_MESGQ;
                        sig_i.si_value = info->notify.sigev_value;
                        /* map current pid/uid into info->owner's namespaces */
                        rcu_read_lock();
                        sig_i.si_pid = task_tgid_nr_ns(current,
                                                ns_of_pid(info->notify_owner));
                        sig_i.si_uid = from_kuid_munged(info->notify_user_ns, current_uid());
                        rcu_read_unlock();

                        kill_pid_info(info->notify.sigev_signo,
                                      &sig_i, info->notify_owner);
                        break;
                case SIGEV_THREAD:
                        set_cookie(info->notify_cookie, NOTIFY_WOKENUP);
                        netlink_sendskb(info->notify_sock, info->notify_cookie);
                        break;
                }
                /* after notification unregisters process */
                put_pid(info->notify_owner);
                put_user_ns(info->notify_user_ns);
                info->notify_owner = NULL;
                info->notify_user_ns = NULL;
        }
        wake_up(&info->wait_q);
}

static int prepare_timeout(const struct timespec __user *u_abs_timeout,
                           struct timespec64 *ts)
{
        if (get_timespec64(ts, u_abs_timeout))
                return -EFAULT;
        if (!timespec64_valid(ts))
                return -EINVAL;
        return 0;
}

static void remove_notification(struct mqueue_inode_info *info)
{
        if (info->notify_owner != NULL &&
            info->notify.sigev_notify == SIGEV_THREAD) {
                set_cookie(info->notify_cookie, NOTIFY_REMOVED);
                netlink_sendskb(info->notify_sock, info->notify_cookie);
        }
        put_pid(info->notify_owner);
        put_user_ns(info->notify_user_ns);
        info->notify_owner = NULL;
        info->notify_user_ns = NULL;
}

static int prepare_open(struct dentry *dentry, int oflag, int ro,
                        umode_t mode, struct filename *name,
                        struct mq_attr *attr)
{
        static const int oflag2acc[O_ACCMODE] = { MAY_READ, MAY_WRITE,
                                                  MAY_READ | MAY_WRITE };
        int acc;

        if (d_really_is_negative(dentry)) {
                if (!(oflag & O_CREAT))
                        return -ENOENT;
                if (ro)
                        return ro;
                audit_inode_parent_hidden(name, dentry->d_parent);
                return vfs_mkobj(dentry, mode & ~current_umask(),
                                  mqueue_create_attr, attr);
        }
        /* it already existed */
        audit_inode(name, dentry, 0);
        if ((oflag & (O_CREAT|O_EXCL)) == (O_CREAT|O_EXCL))
                return -EEXIST;
        if ((oflag & O_ACCMODE) == (O_RDWR | O_WRONLY))
                return -EINVAL;
        acc = oflag2acc[oflag & O_ACCMODE];
        return inode_permission(d_inode(dentry), acc);
}

static int do_mq_open(const char __user *u_name, int oflag, umode_t mode,
                      struct mq_attr *attr)
{
        struct vfsmount *mnt = current->nsproxy->ipc_ns->mq_mnt;
        struct dentry *root = mnt->mnt_root;
        struct filename *name;
        struct path path;
        int fd, error;
        int ro;

        audit_mq_open(oflag, mode, attr);

        if (IS_ERR(name = getname(u_name)))
                return PTR_ERR(name);

        fd = get_unused_fd_flags(O_CLOEXEC);
        if (fd < 0)
                goto out_putname;

        ro = mnt_want_write(mnt);       /* we'll drop it in any case */
        inode_lock(d_inode(root));
        path.dentry = lookup_one_len(name->name, root, strlen(name->name));
        if (IS_ERR(path.dentry)) {
                error = PTR_ERR(path.dentry);
                goto out_putfd;
        }
        path.mnt = mntget(mnt);
        error = prepare_open(path.dentry, oflag, ro, mode, name, attr);
        if (!error) {
                struct file *file = dentry_open(&path, oflag, current_cred());
                if (!IS_ERR(file))
                        fd_install(fd, file);
                else
                        error = PTR_ERR(file);
        }
        path_put(&path);
out_putfd:
        if (error) {
                put_unused_fd(fd);
                fd = error;
        }
        inode_unlock(d_inode(root));
        if (!ro)
                mnt_drop_write(mnt);
out_putname:
        putname(name);
        return fd;
}

SYSCALL_DEFINE4(mq_open, const char __user *, u_name, int, oflag, umode_t, mode,
                struct mq_attr __user *, u_attr)
{
        struct mq_attr attr;
        if (u_attr && copy_from_user(&attr, u_attr, sizeof(struct mq_attr)))
                return -EFAULT;

        return do_mq_open(u_name, oflag, mode, u_attr ? &attr : NULL);
}

SYSCALL_DEFINE1(mq_unlink, const char __user *, u_name)
{
        int err;
        struct filename *name;
        struct dentry *dentry;
        struct inode *inode = NULL;
        struct ipc_namespace *ipc_ns = current->nsproxy->ipc_ns;
        struct vfsmount *mnt = ipc_ns->mq_mnt;

        name = getname(u_name);
        if (IS_ERR(name))
                return PTR_ERR(name);

        audit_inode_parent_hidden(name, mnt->mnt_root);
        err = mnt_want_write(mnt);
        if (err)
                goto out_name;
        inode_lock_nested(d_inode(mnt->mnt_root), I_MUTEX_PARENT);
        dentry = lookup_one_len(name->name, mnt->mnt_root,
                                strlen(name->name));
        if (IS_ERR(dentry)) {
                err = PTR_ERR(dentry);
                goto out_unlock;
        }

        inode = d_inode(dentry);
        if (!inode) {
                err = -ENOENT;
        } else {
                ihold(inode);
                err = vfs_unlink(d_inode(dentry->d_parent), dentry, NULL);
        }
        dput(dentry);

out_unlock:
        inode_unlock(d_inode(mnt->mnt_root));
        if (inode)
                iput(inode);
        mnt_drop_write(mnt);
out_name:
        putname(name);

        return err;
}

/* Pipelined send and receive functions.
 *
 * If a receiver finds no waiting message, then it registers itself in the
 * list of waiting receivers. A sender checks that list before adding the new
 * message into the message array. If there is a waiting receiver, then it
 * bypasses the message array and directly hands the message over to the
 * receiver. The receiver accepts the message and returns without grabbing the
 * queue spinlock:
 *
 * - Set pointer to message.
 * - Queue the receiver task for later wakeup (without the info->lock).
 * - Update its state to STATE_READY. Now the receiver can continue.
 * - Wake up the process after the lock is dropped. Should the process wake up
 *   before this wakeup (due to a timeout or a signal) it will either see
 *   STATE_READY and continue or acquire the lock to check the state again.
 *
 * The same algorithm is used for senders.
 */

/* pipelined_send() - send a message directly to the task waiting in
 * sys_mq_timedreceive() (without inserting message into a queue).
 */
static inline void pipelined_send(struct wake_q_head *wake_q,
                                  struct mqueue_inode_info *info,
                                  struct msg_msg *message,
                                  struct ext_wait_queue *receiver)
{
        receiver->msg = message;
        list_del(&receiver->list);
        wake_q_add(wake_q, receiver->task);
        /*
         * Rely on the implicit cmpxchg barrier from wake_q_add such
         * that we can ensure that updating receiver->state is the last
         * write operation: As once set, the receiver can continue,
         * and if we don't have the reference count from the wake_q,
         * yet, at that point we can later have a use-after-free
         * condition and bogus wakeup.
         */
        receiver->state = STATE_READY;
}

/* pipelined_receive() - if there is task waiting in sys_mq_timedsend()
 * gets its message and put to the queue (we have one free place for sure). */
static inline void pipelined_receive(struct wake_q_head *wake_q,
                                     struct mqueue_inode_info *info)
{
        struct ext_wait_queue *sender = wq_get_first_waiter(info, SEND);

        if (!sender) {
                /* for poll */
                wake_up_interruptible(&info->wait_q);
                return;
        }
        if (msg_insert(sender->msg, info))
                return;

        list_del(&sender->list);
        wake_q_add(wake_q, sender->task);
        sender->state = STATE_READY;
}

static int do_mq_timedsend(mqd_t mqdes, const char __user *u_msg_ptr,
                size_t msg_len, unsigned int msg_prio,
                struct timespec64 *ts)
{
        struct fd f;
        struct inode *inode;
        struct ext_wait_queue wait;
        struct ext_wait_queue *receiver;
        struct msg_msg *msg_ptr;
        struct mqueue_inode_info *info;
        ktime_t expires, *timeout = NULL;
        struct posix_msg_tree_node *new_leaf = NULL;
        int ret = 0;
        DEFINE_WAKE_Q(wake_q);

        if (unlikely(msg_prio >= (unsigned long) MQ_PRIO_MAX))
                return -EINVAL;

        if (ts) {
                expires = timespec64_to_ktime(*ts);
                timeout = &expires;
        }

        audit_mq_sendrecv(mqdes, msg_len, msg_prio, ts);

        f = fdget(mqdes);
        if (unlikely(!f.file)) {
                ret = -EBADF;
                goto out;
        }

        inode = file_inode(f.file);
        if (unlikely(f.file->f_op != &mqueue_file_operations)) {
                ret = -EBADF;
                goto out_fput;
        }
        info = MQUEUE_I(inode);
        audit_file(f.file);

        if (unlikely(!(f.file->f_mode & FMODE_WRITE))) {
                ret = -EBADF;
                goto out_fput;
        }

        if (unlikely(msg_len > info->attr.mq_msgsize)) {
                ret = -EMSGSIZE;
                goto out_fput;
        }

        /* First try to allocate memory, before doing anything with
         * existing queues. */
        msg_ptr = load_msg(u_msg_ptr, msg_len);
        if (IS_ERR(msg_ptr)) {
                ret = PTR_ERR(msg_ptr);
                goto out_fput;
        }
        msg_ptr->m_ts = msg_len;
        msg_ptr->m_type = msg_prio;

        /*
         * msg_insert really wants us to have a valid, spare node struct so
         * it doesn't have to kmalloc a GFP_ATOMIC allocation, but it will
         * fall back to that if necessary.
         */
        if (!info->node_cache)
                new_leaf = kmalloc(sizeof(*new_leaf), GFP_KERNEL);

        spin_lock(&info->lock);

        if (!info->node_cache && new_leaf) {
                /* Save our speculative allocation into the cache */
                INIT_LIST_HEAD(&new_leaf->msg_list);
                info->node_cache = new_leaf;
                new_leaf = NULL;
        } else {
                kfree(new_leaf);
        }

        if (info->attr.mq_curmsgs == info->attr.mq_maxmsg) {
                if (f.file->f_flags & O_NONBLOCK) {
                        ret = -EAGAIN;
                } else {
                        wait.task = current;
                        wait.msg = (void *) msg_ptr;
                        wait.state = STATE_NONE;
                        ret = wq_sleep(info, SEND, timeout, &wait);
                        /*
                         * wq_sleep must be called with info->lock held, and
                         * returns with the lock released
                         */
                        goto out_free;
                }
        } else {
                receiver = wq_get_first_waiter(info, RECV);
                if (receiver) {
                        pipelined_send(&wake_q, info, msg_ptr, receiver);
                } else {
                        /* adds message to the queue */
                        ret = msg_insert(msg_ptr, info);
                        if (ret)
                                goto out_unlock;
                        __do_notify(info);
                }
                inode->i_atime = inode->i_mtime = inode->i_ctime =
                                current_time(inode);
        }
out_unlock:
        spin_unlock(&info->lock);
        wake_up_q(&wake_q);
out_free:
        if (ret)
                free_msg(msg_ptr);
out_fput:
        fdput(f);
out:
        return ret;
}

static int do_mq_timedreceive(mqd_t mqdes, char __user *u_msg_ptr,
                size_t msg_len, unsigned int __user *u_msg_prio,
                struct timespec64 *ts)
{
        ssize_t ret;
        struct msg_msg *msg_ptr;
        struct fd f;
        struct inode *inode;
        struct mqueue_inode_info *info;
        struct ext_wait_queue wait;
        ktime_t expires, *timeout = NULL;
        struct posix_msg_tree_node *new_leaf = NULL;

        if (ts) {
                expires = timespec64_to_ktime(*ts);
                timeout = &expires;
        }

        audit_mq_sendrecv(mqdes, msg_len, 0, ts);

        f = fdget(mqdes);
        if (unlikely(!f.file)) {
                ret = -EBADF;
                goto out;
        }

        inode = file_inode(f.file);
        if (unlikely(f.file->f_op != &mqueue_file_operations)) {
                ret = -EBADF;
                goto out_fput;
        }
        info = MQUEUE_I(inode);
        audit_file(f.file);

        if (unlikely(!(f.file->f_mode & FMODE_READ))) {
                ret = -EBADF;
                goto out_fput;
        }

        /* checks if buffer is big enough */
        if (unlikely(msg_len < info->attr.mq_msgsize)) {
                ret = -EMSGSIZE;
                goto out_fput;
        }

        /*
         * msg_insert really wants us to have a valid, spare node struct so
         * it doesn't have to kmalloc a GFP_ATOMIC allocation, but it will
         * fall back to that if necessary.
         */
        if (!info->node_cache)
                new_leaf = kmalloc(sizeof(*new_leaf), GFP_KERNEL);

        spin_lock(&info->lock);

        if (!info->node_cache && new_leaf) {
                /* Save our speculative allocation into the cache */
                INIT_LIST_HEAD(&new_leaf->msg_list);
                info->node_cache = new_leaf;
        } else {
                kfree(new_leaf);
        }

        if (info->attr.mq_curmsgs == 0) {
                if (f.file->f_flags & O_NONBLOCK) {
                        spin_unlock(&info->lock);
                        ret = -EAGAIN;
                } else {
                        wait.task = current;
                        wait.state = STATE_NONE;
                        ret = wq_sleep(info, RECV, timeout, &wait);
                        msg_ptr = wait.msg;
                }
        } else {
                DEFINE_WAKE_Q(wake_q);

                msg_ptr = msg_get(info);

                inode->i_atime = inode->i_mtime = inode->i_ctime =
                                current_time(inode);

                /* There is now free space in queue. */
                pipelined_receive(&wake_q, info);
                spin_unlock(&info->lock);
                wake_up_q(&wake_q);
                ret = 0;
        }
        if (ret == 0) {
                ret = msg_ptr->m_ts;

                if ((u_msg_prio && put_user(msg_ptr->m_type, u_msg_prio)) ||
                        store_msg(u_msg_ptr, msg_ptr, msg_ptr->m_ts)) {
                        ret = -EFAULT;
                }
                free_msg(msg_ptr);
        }
out_fput:
        fdput(f);
out:
        return ret;
}

SYSCALL_DEFINE5(mq_timedsend, mqd_t, mqdes, const char __user *, u_msg_ptr,
                size_t, msg_len, unsigned int, msg_prio,
                const struct timespec __user *, u_abs_timeout)
{
        struct timespec64 ts, *p = NULL;
        if (u_abs_timeout) {
                int res = prepare_timeout(u_abs_timeout, &ts);
                if (res)
                        return res;
                p = &ts;
        }
        return do_mq_timedsend(mqdes, u_msg_ptr, msg_len, msg_prio, p);
}

SYSCALL_DEFINE5(mq_timedreceive, mqd_t, mqdes, char __user *, u_msg_ptr,
                size_t, msg_len, unsigned int __user *, u_msg_prio,
                const struct timespec __user *, u_abs_timeout)
{
        struct timespec64 ts, *p = NULL;
        if (u_abs_timeout) {
                int res = prepare_timeout(u_abs_timeout, &ts);
                if (res)
                        return res;
                p = &ts;
        }
        return do_mq_timedreceive(mqdes, u_msg_ptr, msg_len, u_msg_prio, p);
}

/*
 * Notes: the case when user wants us to deregister (with NULL as pointer)
 * and he isn't currently owner of notification, will be silently discarded.
 * It isn't explicitly defined in the POSIX.
 */
static int do_mq_notify(mqd_t mqdes, const struct sigevent *notification)
{
        int ret;
        struct fd f;
        struct sock *sock;
        struct inode *inode;
        struct mqueue_inode_info *info;
        struct sk_buff *nc;

        audit_mq_notify(mqdes, notification);

        nc = NULL;
        sock = NULL;
        if (notification != NULL) {
                if (unlikely(notification->sigev_notify != SIGEV_NONE &&
                             notification->sigev_notify != SIGEV_SIGNAL &&
                             notification->sigev_notify != SIGEV_THREAD))
                        return -EINVAL;
                if (notification->sigev_notify == SIGEV_SIGNAL &&
                        !valid_signal(notification->sigev_signo)) {
                        return -EINVAL;
                }
                if (notification->sigev_notify == SIGEV_THREAD) {
                        long timeo;

                        /* create the notify skb */
                        nc = alloc_skb(NOTIFY_COOKIE_LEN, GFP_KERNEL);
                        if (!nc) {
                                ret = -ENOMEM;
                                goto out;
                        }
                        if (copy_from_user(nc->data,
                                        notification->sigev_value.sival_ptr,
                                        NOTIFY_COOKIE_LEN)) {
                                ret = -EFAULT;
                                goto out;
                        }

                        /* TODO: add a header? */
                        skb_put(nc, NOTIFY_COOKIE_LEN);
                        /* and attach it to the socket */
retry:
                        f = fdget(notification->sigev_signo);
                        if (!f.file) {
                                ret = -EBADF;
                                goto out;
                        }
                        sock = netlink_getsockbyfilp(f.file);
                        fdput(f);
                        if (IS_ERR(sock)) {
                                ret = PTR_ERR(sock);
                                sock = NULL;
                                goto out;
                        }

                        timeo = MAX_SCHEDULE_TIMEOUT;
                        ret = netlink_attachskb(sock, nc, &timeo, NULL);
                        if (ret == 1) {
                                sock = NULL;
                                goto retry;
                        }
                        if (ret) {
                                sock = NULL;
                                nc = NULL;
                                goto out;
                        }
                }
        }

        f = fdget(mqdes);
        if (!f.file) {
                ret = -EBADF;
                goto out;
        }

        inode = file_inode(f.file);
        if (unlikely(f.file->f_op != &mqueue_file_operations)) {
                ret = -EBADF;
                goto out_fput;
        }
        info = MQUEUE_I(inode);

        ret = 0;
        spin_lock(&info->lock);
        if (notification == NULL) {
                if (info->notify_owner == task_tgid(current)) {
                        remove_notification(info);
                        inode->i_atime = inode->i_ctime = current_time(inode);
                }
        } else if (info->notify_owner != NULL) {
                ret = -EBUSY;
        } else {
                switch (notification->sigev_notify) {
                case SIGEV_NONE:
                        info->notify.sigev_notify = SIGEV_NONE;
                        break;
                case SIGEV_THREAD:
                        info->notify_sock = sock;
                        info->notify_cookie = nc;
                        sock = NULL;
                        nc = NULL;
                        info->notify.sigev_notify = SIGEV_THREAD;
                        break;
                case SIGEV_SIGNAL:
                        info->notify.sigev_signo = notification->sigev_signo;
                        info->notify.sigev_value = notification->sigev_value;
                        info->notify.sigev_notify = SIGEV_SIGNAL;
                        break;
                }

                info->notify_owner = get_pid(task_tgid(current));
                info->notify_user_ns = get_user_ns(current_user_ns());
                inode->i_atime = inode->i_ctime = current_time(inode);
        }
        spin_unlock(&info->lock);
out_fput:
        fdput(f);
out:
        if (sock)
                netlink_detachskb(sock, nc);
        else if (nc)
                dev_kfree_skb(nc);

        return ret;
}

SYSCALL_DEFINE2(mq_notify, mqd_t, mqdes,
                const struct sigevent __user *, u_notification)
{
        struct sigevent n, *p = NULL;
        if (u_notification) {
                if (copy_from_user(&n, u_notification, sizeof(struct sigevent)))
                        return -EFAULT;
                p = &n;
        }
        return do_mq_notify(mqdes, p);
}

static int do_mq_getsetattr(int mqdes, struct mq_attr *new, struct mq_attr *old)
{
        struct fd f;
        struct inode *inode;
        struct mqueue_inode_info *info;

        if (new && (new->mq_flags & (~O_NONBLOCK)))
                return -EINVAL;

        f = fdget(mqdes);
        if (!f.file)
                return -EBADF;

        if (unlikely(f.file->f_op != &mqueue_file_operations)) {
                fdput(f);
                return -EBADF;
        }

        inode = file_inode(f.file);
        info = MQUEUE_I(inode);

        spin_lock(&info->lock);

        if (old) {
                *old = info->attr;
                old->mq_flags = f.file->f_flags & O_NONBLOCK;
        }
        if (new) {
                audit_mq_getsetattr(mqdes, new);
                spin_lock(&f.file->f_lock);
                if (new->mq_flags & O_NONBLOCK)
                        f.file->f_flags |= O_NONBLOCK;
                else
                        f.file->f_flags &= ~O_NONBLOCK;
                spin_unlock(&f.file->f_lock);

                inode->i_atime = inode->i_ctime = current_time(inode);
        }

        spin_unlock(&info->lock);
        fdput(f);
        return 0;
}

SYSCALL_DEFINE3(mq_getsetattr, mqd_t, mqdes,
                const struct mq_attr __user *, u_mqstat,
                struct mq_attr __user *, u_omqstat)
{
        int ret;
        struct mq_attr mqstat, omqstat;
        struct mq_attr *new = NULL, *old = NULL;

        if (u_mqstat) {
                new = &mqstat;
                if (copy_from_user(new, u_mqstat, sizeof(struct mq_attr)))
                        return -EFAULT;
        }
        if (u_omqstat)
                old = &omqstat;

        ret = do_mq_getsetattr(mqdes, new, old);
        if (ret || !old)
                return ret;

        if (copy_to_user(u_omqstat, old, sizeof(struct mq_attr)))
                return -EFAULT;
        return 0;
}

#ifdef CONFIG_COMPAT

struct compat_mq_attr {
        compat_long_t mq_flags;      /* message queue flags                  */
        compat_long_t mq_maxmsg;     /* maximum number of messages           */
        compat_long_t mq_msgsize;    /* maximum message size                 */
        compat_long_t mq_curmsgs;    /* number of messages currently queued  */
        compat_long_t __reserved[4]; /* ignored for input, zeroed for output */
};

static inline int get_compat_mq_attr(struct mq_attr *attr,
                        const struct compat_mq_attr __user *uattr)
{
        struct compat_mq_attr v;

        if (copy_from_user(&v, uattr, sizeof(*uattr)))
                return -EFAULT;

        memset(attr, 0, sizeof(*attr));
        attr->mq_flags = v.mq_flags;
        attr->mq_maxmsg = v.mq_maxmsg;
        attr->mq_msgsize = v.mq_msgsize;
        attr->mq_curmsgs = v.mq_curmsgs;
        return 0;
}

static inline int put_compat_mq_attr(const struct mq_attr *attr,
                        struct compat_mq_attr __user *uattr)
{
        struct compat_mq_attr v;

        memset(&v, 0, sizeof(v));
        v.mq_flags = attr->mq_flags;
        v.mq_maxmsg = attr->mq_maxmsg;
        v.mq_msgsize = attr->mq_msgsize;
        v.mq_curmsgs = attr->mq_curmsgs;
        if (copy_to_user(uattr, &v, sizeof(*uattr)))
                return -EFAULT;
        return 0;
}

COMPAT_SYSCALL_DEFINE4(mq_open, const char __user *, u_name,
                       int, oflag, compat_mode_t, mode,
                       struct compat_mq_attr __user *, u_attr)
{
        struct mq_attr attr, *p = NULL;
        if (u_attr && oflag & O_CREAT) {
                p = &attr;
                if (get_compat_mq_attr(&attr, u_attr))
                        return -EFAULT;
        }
        return do_mq_open(u_name, oflag, mode, p);
}

static int compat_prepare_timeout(const struct compat_timespec __user *p,
                                   struct timespec64 *ts)
{
        if (compat_get_timespec64(ts, p))
                return -EFAULT;
        if (!timespec64_valid(ts))
                return -EINVAL;
        return 0;
}

COMPAT_SYSCALL_DEFINE5(mq_timedsend, mqd_t, mqdes,
                       const char __user *, u_msg_ptr,
                       compat_size_t, msg_len, unsigned int, msg_prio,
                       const struct compat_timespec __user *, u_abs_timeout)
{
        struct timespec64 ts, *p = NULL;
        if (u_abs_timeout) {
                int res = compat_prepare_timeout(u_abs_timeout, &ts);
                if (res)
                        return res;
                p = &ts;
        }
        return do_mq_timedsend(mqdes, u_msg_ptr, msg_len, msg_prio, p);
}

COMPAT_SYSCALL_DEFINE5(mq_timedreceive, mqd_t, mqdes,
                       char __user *, u_msg_ptr,
                       compat_size_t, msg_len, unsigned int __user *, u_msg_prio,
                       const struct compat_timespec __user *, u_abs_timeout)
{
        struct timespec64 ts, *p = NULL;
        if (u_abs_timeout) {
                int res = compat_prepare_timeout(u_abs_timeout, &ts);
                if (res)
                        return res;
                p = &ts;
        }
        return do_mq_timedreceive(mqdes, u_msg_ptr, msg_len, u_msg_prio, p);
}

COMPAT_SYSCALL_DEFINE2(mq_notify, mqd_t, mqdes,
                       const struct compat_sigevent __user *, u_notification)
{
        struct sigevent n, *p = NULL;
        if (u_notification) {
                if (get_compat_sigevent(&n, u_notification))
                        return -EFAULT;
                if (n.sigev_notify == SIGEV_THREAD)
                        n.sigev_value.sival_ptr = compat_ptr(n.sigev_value.sival_int);
                p = &n;
        }
        return do_mq_notify(mqdes, p);
}

COMPAT_SYSCALL_DEFINE3(mq_getsetattr, mqd_t, mqdes,
                       const struct compat_mq_attr __user *, u_mqstat,
                       struct compat_mq_attr __user *, u_omqstat)
{
        int ret;
        struct mq_attr mqstat, omqstat;
        struct mq_attr *new = NULL, *old = NULL;

        if (u_mqstat) {
                new = &mqstat;
                if (get_compat_mq_attr(new, u_mqstat))
                        return -EFAULT;
        }
        if (u_omqstat)
                old = &omqstat;

        ret = do_mq_getsetattr(mqdes, new, old);
        if (ret || !old)
                return ret;

        if (put_compat_mq_attr(old, u_omqstat))
                return -EFAULT;
        return 0;
}
#endif

static const struct inode_operations mqueue_dir_inode_operations = {
        .lookup = simple_lookup,
        .create = mqueue_create,
        .unlink = mqueue_unlink,
};

static const struct file_operations mqueue_file_operations = {
        .flush = mqueue_flush_file,
        .poll = mqueue_poll_file,
        .read = mqueue_read_file,
        .llseek = default_llseek,
};

static const struct super_operations mqueue_super_ops = {
        .alloc_inode = mqueue_alloc_inode,
        .destroy_inode = mqueue_destroy_inode,
        .evict_inode = mqueue_evict_inode,
        .statfs = simple_statfs,
};

static struct file_system_type mqueue_fs_type = {
        .name = "mqueue",
        .mount = mqueue_mount,
        .kill_sb = kill_litter_super,
        .fs_flags = FS_USERNS_MOUNT,
};

int mq_init_ns(struct ipc_namespace *ns)
{
        ns->mq_queues_count  = 0;
        ns->mq_queues_max    = DFLT_QUEUESMAX;
        ns->mq_msg_max       = DFLT_MSGMAX;
        ns->mq_msgsize_max   = DFLT_MSGSIZEMAX;
        ns->mq_msg_default   = DFLT_MSG;
        ns->mq_msgsize_default  = DFLT_MSGSIZE;

        ns->mq_mnt = kern_mount_data(&mqueue_fs_type, ns);
        if (IS_ERR(ns->mq_mnt)) {
                int err = PTR_ERR(ns->mq_mnt);
                ns->mq_mnt = NULL;
                return err;
        }
        return 0;
}

void mq_clear_sbinfo(struct ipc_namespace *ns)
{
        ns->mq_mnt->mnt_sb->s_fs_info = NULL;
}

void mq_put_mnt(struct ipc_namespace *ns)
{
        kern_unmount(ns->mq_mnt);
}

static int __init init_mqueue_fs(void)
{
        int error;

        mqueue_inode_cachep = kmem_cache_create("mqueue_inode_cache",
                                sizeof(struct mqueue_inode_info), 0,
                                SLAB_HWCACHE_ALIGN|SLAB_ACCOUNT, init_once);
        if (mqueue_inode_cachep == NULL)
                return -ENOMEM;

        /* ignore failures - they are not fatal */
        mq_sysctl_table = mq_register_sysctl_table();

        error = register_filesystem(&mqueue_fs_type);
        if (error)
                goto out_sysctl;

        spin_lock_init(&mq_lock);

        error = mq_init_ns(&init_ipc_ns);
        if (error)
                goto out_filesystem;

        return 0;

out_filesystem:
        unregister_filesystem(&mqueue_fs_type);
out_sysctl:
        if (mq_sysctl_table)
                unregister_sysctl_table(mq_sysctl_table);
        kmem_cache_destroy(mqueue_inode_cachep);
        return error;
}

device_initcall(init_mqueue_fs);