#include <linux/fanotify.h>
#include <linux/fdtable.h>
#include <linux/fsnotify_backend.h>
#include <linux/init.h>
#include <linux/jiffies.h>
#include <linux/kernel.h> /* UINT_MAX */
#include <linux/mount.h>
#include <linux/sched.h>
#include <linux/types.h>
#include <linux/wait.h>

#include "fanotify.h"

static bool should_merge(struct fsnotify_event *old_fsn,
                         struct fsnotify_event *new_fsn)
{
        struct fanotify_event_info *old, *new;

        pr_debug("%s: old=%p new=%p\n", __func__, old_fsn, new_fsn);
        old = FANOTIFY_E(old_fsn);
        new = FANOTIFY_E(new_fsn);

        if (old_fsn->inode == new_fsn->inode && old->tgid == new->tgid &&
            old->path.mnt == new->path.mnt &&
            old->path.dentry == new->path.dentry)
                return true;
        return false;
}

/* and the list better be locked by something too! */
static int fanotify_merge(struct list_head *list, struct fsnotify_event *event)
{
        struct fsnotify_event *test_event;
        bool do_merge = false;

        pr_debug("%s: list=%p event=%p\n", __func__, list, event);

#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
        /*
         * Don't merge a permission event with any other event so that we know
         * the event structure we have created in fanotify_handle_event() is the
         * one we should check for permission response.
         */
        if (event->mask & FAN_ALL_PERM_EVENTS)
                return 0;
#endif

        list_for_each_entry_reverse(test_event, list, list) {
                if (should_merge(test_event, event)) {
                        do_merge = true;
                        break;
                }
        }

        if (!do_merge)
                return 0;

        test_event->mask |= event->mask;
        return 1;
}

#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
static int fanotify_get_response_from_access(struct fsnotify_group *group,
                                             struct fanotify_event_info *event)
{
        int ret;

        pr_debug("%s: group=%p event=%p\n", __func__, group, event);

        wait_event(group->fanotify_data.access_waitq, event->response ||
                                atomic_read(&group->fanotify_data.bypass_perm));

        if (!event->response) /* bypass_perm set */
                return 0;

        /* userspace responded, convert to something usable */
        switch (event->response) {
        case FAN_ALLOW:
                ret = 0;
                break;
        case FAN_DENY:
        default:
                ret = -EPERM;
        }
        event->response = 0;

        pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
                 group, event, ret);
        
        return ret;
}
#endif

static bool fanotify_should_send_event(struct fsnotify_mark *inode_mark,
                                       struct fsnotify_mark *vfsmnt_mark,
                                       u32 event_mask,
                                       void *data, int data_type)
{
        __u32 marks_mask, marks_ignored_mask;
        struct path *path = data;

        pr_debug("%s: inode_mark=%p vfsmnt_mark=%p mask=%x data=%p"
                 " data_type=%d\n", __func__, inode_mark, vfsmnt_mark,
                 event_mask, data, data_type);

        /* if we don't have enough info to send an event to userspace say no */
        if (data_type != FSNOTIFY_EVENT_PATH)
                return false;

        /* sorry, fanotify only gives a damn about files and dirs */
        if (!S_ISREG(path->dentry->d_inode->i_mode) &&
            !S_ISDIR(path->dentry->d_inode->i_mode))
                return false;

        if (inode_mark && vfsmnt_mark) {
                marks_mask = (vfsmnt_mark->mask | inode_mark->mask);
                marks_ignored_mask = (vfsmnt_mark->ignored_mask | inode_mark->ignored_mask);
        } else if (inode_mark) {
                /*
                 * if the event is for a child and this inode doesn't care about
                 * events on the child, don't send it!
                 */
                if ((event_mask & FS_EVENT_ON_CHILD) &&
                    !(inode_mark->mask & FS_EVENT_ON_CHILD))
                        return false;
                marks_mask = inode_mark->mask;
                marks_ignored_mask = inode_mark->ignored_mask;
        } else if (vfsmnt_mark) {
                marks_mask = vfsmnt_mark->mask;
                marks_ignored_mask = vfsmnt_mark->ignored_mask;
        } else {
                BUG();
        }

        if (S_ISDIR(path->dentry->d_inode->i_mode) &&
            (marks_ignored_mask & FS_ISDIR))
                return false;

        if (event_mask & marks_mask & ~marks_ignored_mask)
                return true;

        return false;
}

static int fanotify_handle_event(struct fsnotify_group *group,
                                 struct inode *inode,
                                 struct fsnotify_mark *inode_mark,
                                 struct fsnotify_mark *fanotify_mark,
                                 u32 mask, void *data, int data_type,
                                 const unsigned char *file_name, u32 cookie)
{
        int ret = 0;
        struct fanotify_event_info *event;
        struct fsnotify_event *fsn_event;

        BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
        BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
        BUILD_BUG_ON(FAN_CLOSE_NOWRITE != FS_CLOSE_NOWRITE);
        BUILD_BUG_ON(FAN_CLOSE_WRITE != FS_CLOSE_WRITE);
        BUILD_BUG_ON(FAN_OPEN != FS_OPEN);
        BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
        BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
        BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
        BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
        BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);

        if (!fanotify_should_send_event(inode_mark, fanotify_mark, mask, data,
                                        data_type))
                return 0;

        pr_debug("%s: group=%p inode=%p mask=%x\n", __func__, group, inode,
                 mask);

        event = kmem_cache_alloc(fanotify_event_cachep, GFP_KERNEL);
        if (unlikely(!event))
                return -ENOMEM;

        fsn_event = &event->fse;
        fsnotify_init_event(fsn_event, inode, mask);
        event->tgid = get_pid(task_tgid(current));
        if (data_type == FSNOTIFY_EVENT_PATH) {
                struct path *path = data;
                event->path = *path;
                path_get(&event->path);
        } else {
                event->path.mnt = NULL;
                event->path.dentry = NULL;
        }
#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
        event->response = 0;
#endif

        ret = fsnotify_add_notify_event(group, fsn_event, fanotify_merge);
        if (ret) {
                /* Permission events shouldn't be merged */
                BUG_ON(ret == 1 && mask & FAN_ALL_PERM_EVENTS);
                /* Our event wasn't used in the end. Free it. */
                fsnotify_destroy_event(group, fsn_event);

                return 0;
        }

#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
        if (mask & FAN_ALL_PERM_EVENTS) {
                ret = fanotify_get_response_from_access(group, event);
                fsnotify_destroy_event(group, fsn_event);
        }
#endif
        return ret;
}

static void fanotify_free_group_priv(struct fsnotify_group *group)
{
        struct user_struct *user;

        user = group->fanotify_data.user;
        atomic_dec(&user->fanotify_listeners);
        free_uid(user);
}

static void fanotify_free_event(struct fsnotify_event *fsn_event)
{
        struct fanotify_event_info *event;

        event = FANOTIFY_E(fsn_event);
        path_put(&event->path);
        put_pid(event->tgid);
        kmem_cache_free(fanotify_event_cachep, event);
}

const struct fsnotify_ops fanotify_fsnotify_ops = {
        .handle_event = fanotify_handle_event,
        .free_group_priv = fanotify_free_group_priv,
        .free_event = fanotify_free_event,
};