mqueue.c

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/*
 * POSIX message queues filesystem for Linux.
 *
 * Copyright (C) 2003,2004  Krzysztof Benedyczak    ([email protected])
 *                          Michal Wronski          ([email protected])
 *
 * Spinlocks:               Mohamed Abbas           ([email protected])
 * Lockless receive & send, fd based notify:
 *              Manfred Spraul      ([email protected])
 *
 * Audit:                   George Wilson           ([email protected])
 *
 * 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 <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_PENDING   1
#define STATE_READY 2

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);
        info->qsize += sizeof(*leaf);
    }
    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) {
            info->qsize -= sizeof(*leaf);
            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) {
                info->qsize -= sizeof(*leaf);
                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;

    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.
         */
        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);

        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 = data;

    sb->s_blocksize = PAGE_CACHE_SIZE;
    sb->s_blocksize_bits = PAGE_CACHE_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)
{
    if (!(flags & MS_KERNMOUNT))
        data = current->nsproxy->ipc_ns;
    return mount_ns(fs_type, flags, data, 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(struct inode *dir, struct dentry *dentry,
                umode_t mode, bool excl)
{
    struct inode *inode;
    struct mq_attr *attr = dentry->d_fsdata;
    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 >= HARD_QUEUESMAX ||
        (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;

    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_unlink(struct inode *dir, struct dentry *dentry)
{
    struct inode *inode = dentry->d_inode;

    dir->i_ctime = dir->i_mtime = dir->i_atime = CURRENT_TIME;
    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(filp->f_path.dentry->d_inode);
    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;

    filp->f_path.dentry->d_inode->i_atime = filp->f_path.dentry->d_inode->i_ctime = CURRENT_TIME;
    return ret;
}

static int mqueue_flush_file(struct file *filp, fl_owner_t id)
{
    struct mqueue_inode_info *info = MQUEUE_I(filp->f_path.dentry->d_inode);

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

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

static unsigned int mqueue_poll_file(struct file *filp, struct poll_table_struct *poll_tab)
{
    struct mqueue_inode_info *info = MQUEUE_I(filp->f_path.dentry->d_inode);
    int retval = 0;

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

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

    if (info->attr.mq_curmsgs < info->attr.mq_maxmsg)
        retval |= POLLOUT | POLLWRNORM;
    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->static_prio <= current->static_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)
{
    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);

        while (ewp->state == STATE_PENDING)
            cpu_relax();

        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 */

            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,
               ktime_t *expires, struct timespec *ts)
{
    if (copy_from_user(ts, u_abs_timeout, sizeof(struct timespec)))
        return -EFAULT;
    if (!timespec_valid(ts))
        return -EINVAL;

    *expires = timespec_to_ktime(*ts);
    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 mq_attr_ok(struct ipc_namespace *ipc_ns, struct mq_attr *attr)
{
    int mq_treesize;
    unsigned long total_size;

    if (attr->mq_maxmsg <= 0 || attr->mq_msgsize <= 0)
        return -EINVAL;
    if (capable(CAP_SYS_RESOURCE)) {
        if (attr->mq_maxmsg > HARD_MSGMAX ||
            attr->mq_msgsize > HARD_MSGSIZEMAX)
            return -EINVAL;
    } else {
        if (attr->mq_maxmsg > ipc_ns->mq_msg_max ||
                attr->mq_msgsize > ipc_ns->mq_msgsize_max)
            return -EINVAL;
    }
    /* check for overflow */
    if (attr->mq_msgsize > ULONG_MAX/attr->mq_maxmsg)
        return -EOVERFLOW;
    mq_treesize = attr->mq_maxmsg * sizeof(struct msg_msg) +
        min_t(unsigned int, attr->mq_maxmsg, MQ_PRIO_MAX) *
        sizeof(struct posix_msg_tree_node);
    total_size = attr->mq_maxmsg * attr->mq_msgsize;
    if (total_size + mq_treesize < total_size)
        return -EOVERFLOW;
    return 0;
}

/*
 * Invoked when creating a new queue via sys_mq_open
 */
static struct file *do_create(struct ipc_namespace *ipc_ns, struct inode *dir,
            struct path *path, int oflag, umode_t mode,
            struct mq_attr *attr)
{
    const struct cred *cred = current_cred();
    int ret;

    if (attr) {
        ret = mq_attr_ok(ipc_ns, attr);
        if (ret)
            return ERR_PTR(ret);
        /* store for use during create */
        path->dentry->d_fsdata = attr;
    } else {
        struct mq_attr def_attr;

        def_attr.mq_maxmsg = min(ipc_ns->mq_msg_max,
                     ipc_ns->mq_msg_default);
        def_attr.mq_msgsize = min(ipc_ns->mq_msgsize_max,
                      ipc_ns->mq_msgsize_default);
        ret = mq_attr_ok(ipc_ns, &def_attr);
        if (ret)
            return ERR_PTR(ret);
    }

    mode &= ~current_umask();
    ret = vfs_create(dir, path->dentry, mode, true);
    path->dentry->d_fsdata = NULL;
    if (ret)
        return ERR_PTR(ret);
    return dentry_open(path, oflag, cred);
}

/* Opens existing queue */
static struct file *do_open(struct path *path, int oflag)
{
    static const int oflag2acc[O_ACCMODE] = { MAY_READ, MAY_WRITE,
                          MAY_READ | MAY_WRITE };
    int acc;
    if ((oflag & O_ACCMODE) == (O_RDWR | O_WRONLY))
        return ERR_PTR(-EINVAL);
    acc = oflag2acc[oflag & O_ACCMODE];
    if (inode_permission(path->dentry->d_inode, acc))
        return ERR_PTR(-EACCES);
    return dentry_open(path, oflag, current_cred());
}

SYSCALL_DEFINE4(mq_open, const char __user *, u_name, int, oflag, umode_t, mode,
        struct mq_attr __user *, u_attr)
{
    struct path path;
    struct file *filp;
    struct filename *name;
    struct mq_attr attr;
    int fd, error;
    struct ipc_namespace *ipc_ns = current->nsproxy->ipc_ns;
    struct vfsmount *mnt = ipc_ns->mq_mnt;
    struct dentry *root = mnt->mnt_root;
    int ro;

    if (u_attr && copy_from_user(&attr, u_attr, sizeof(struct mq_attr)))
        return -EFAULT;

    audit_mq_open(oflag, mode, u_attr ? &attr : NULL);

    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 */
    error = 0;
    mutex_lock(&root->d_inode->i_mutex);
    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);

    if (oflag & O_CREAT) {
        if (path.dentry->d_inode) { /* entry already exists */
            audit_inode(name, path.dentry, 0);
            if (oflag & O_EXCL) {
                error = -EEXIST;
                goto out;
            }
            filp = do_open(&path, oflag);
        } else {
            if (ro) {
                error = ro;
                goto out;
            }
            filp = do_create(ipc_ns, root->d_inode,
                        &path, oflag, mode,
                        u_attr ? &attr : NULL);
        }
    } else {
        if (!path.dentry->d_inode) {
            error = -ENOENT;
            goto out;
        }
        audit_inode(name, path.dentry, 0);
        filp = do_open(&path, oflag);
    }

    if (!IS_ERR(filp))
        fd_install(fd, filp);
    else
        error = PTR_ERR(filp);
out:
    path_put(&path);
out_putfd:
    if (error) {
        put_unused_fd(fd);
        fd = error;
    }
    mutex_unlock(&root->d_inode->i_mutex);
    mnt_drop_write(mnt);
out_putname:
    putname(name);
    return fd;
}

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);

    err = mnt_want_write(mnt);
    if (err)
        goto out_name;
    mutex_lock_nested(&mnt->mnt_root->d_inode->i_mutex, 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 = dentry->d_inode;
    if (!inode) {
        err = -ENOENT;
    } else {
        ihold(inode);
        err = vfs_unlink(dentry->d_parent->d_inode, dentry);
    }
    dput(dentry);

out_unlock:
    mutex_unlock(&mnt->mnt_root->d_inode->i_mutex);
    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. Therefore an intermediate STATE_PENDING state and memory barriers
 * are necessary. The same algorithm is used for sysv semaphores, see
 * ipc/sem.c for more details.
 *
 * 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 mqueue_inode_info *info,
                  struct msg_msg *message,
                  struct ext_wait_queue *receiver)
{
    receiver->msg = message;
    list_del(&receiver->list);
    receiver->state = STATE_PENDING;
    wake_up_process(receiver->task);
    smp_wmb();
    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 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);
    sender->state = STATE_PENDING;
    wake_up_process(sender->task);
    smp_wmb();
    sender->state = STATE_READY;
}

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 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 timespec ts;
    struct posix_msg_tree_node *new_leaf = NULL;
    int ret = 0;

    if (u_abs_timeout) {
        int res = prepare_timeout(u_abs_timeout, &expires, &ts);
        if (res)
            return res;
        timeout = &expires;
    }

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

    audit_mq_sendrecv(mqdes, msg_len, msg_prio, timeout ? &ts : NULL);

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

    inode = f.file->f_path.dentry->d_inode;
    if (unlikely(f.file->f_op != &mqueue_file_operations)) {
        ret = -EBADF;
        goto out_fput;
    }
    info = MQUEUE_I(inode);
    audit_inode(NULL, f.file->f_path.dentry, 0);

    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;
        info->qsize += sizeof(*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(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;
    }
out_unlock:
    spin_unlock(&info->lock);
out_free:
    if (ret)
        free_msg(msg_ptr);
out_fput:
    fdput(f);
out:
    return ret;
}

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)
{
    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 timespec ts;
    struct posix_msg_tree_node *new_leaf = NULL;

    if (u_abs_timeout) {
        int res = prepare_timeout(u_abs_timeout, &expires, &ts);
        if (res)
            return res;
        timeout = &expires;
    }

    audit_mq_sendrecv(mqdes, msg_len, 0, timeout ? &ts : NULL);

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

    inode = f.file->f_path.dentry->d_inode;
    if (unlikely(f.file->f_op != &mqueue_file_operations)) {
        ret = -EBADF;
        goto out_fput;
    }
    info = MQUEUE_I(inode);
    audit_inode(NULL, f.file->f_path.dentry, 0);

    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;
        info->qsize += sizeof(*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 {
        msg_ptr = msg_get(info);

        inode->i_atime = inode->i_mtime = inode->i_ctime =
                CURRENT_TIME;

        /* There is now free space in queue. */
        pipelined_receive(info);
        spin_unlock(&info->lock);
        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;
}

/*
 * 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.
 */
SYSCALL_DEFINE2(mq_notify, mqd_t, mqdes,
        const struct sigevent __user *, u_notification)
{
    int ret;
    struct fd f;
    struct sock *sock;
    struct inode *inode;
    struct sigevent notification;
    struct mqueue_inode_info *info;
    struct sk_buff *nc;

    if (u_notification) {
        if (copy_from_user(&notification, u_notification,
                    sizeof(struct sigevent)))
            return -EFAULT;
    }

    audit_mq_notify(mqdes, u_notification ? &notification : NULL);

    nc = NULL;
    sock = NULL;
    if (u_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)
                goto retry;
            if (ret) {
                sock = NULL;
                nc = NULL;
                goto out;
            }
        }
    }

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

    inode = f.file->f_path.dentry->d_inode;
    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 (u_notification == NULL) {
        if (info->notify_owner == task_tgid(current)) {
            remove_notification(info);
            inode->i_atime = inode->i_ctime = CURRENT_TIME;
        }
    } 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;
    }
    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_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 fd f;
    struct inode *inode;
    struct mqueue_inode_info *info;

    if (u_mqstat != NULL) {
        if (copy_from_user(&mqstat, u_mqstat, sizeof(struct mq_attr)))
            return -EFAULT;
        if (mqstat.mq_flags & (~O_NONBLOCK))
            return -EINVAL;
    }

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

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

    spin_lock(&info->lock);

    omqstat = info->attr;
    omqstat.mq_flags = f.file->f_flags & O_NONBLOCK;
    if (u_mqstat) {
        audit_mq_getsetattr(mqdes, &mqstat);
        spin_lock(&f.file->f_lock);
        if (mqstat.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;
    }

    spin_unlock(&info->lock);

    ret = 0;
    if (u_omqstat != NULL && copy_to_user(u_omqstat, &omqstat,
                        sizeof(struct mq_attr)))
        ret = -EFAULT;

out_fput:
    fdput(f);
out:
    return ret;
}

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,
};

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, 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;
}

__initcall(init_mqueue_fs);