// SPDX-License-Identifier: GPL-2.0
#include <linux/fanotify.h>
#include <linux/fcntl.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/anon_inodes.h>
#include <linux/fsnotify_backend.h>
#include <linux/init.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/poll.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/uaccess.h>
#include <linux/compat.h>
#include <linux/sched/signal.h>
#include <linux/memcontrol.h>
#include <linux/statfs.h>
#include <linux/exportfs.h>

#include <asm/ioctls.h>

#include "../../mount.h"
#include "../fdinfo.h"
#include "fanotify.h"

#define FANOTIFY_DEFAULT_MAX_EVENTS     16384
#define FANOTIFY_DEFAULT_MAX_MARKS      8192
#define FANOTIFY_DEFAULT_MAX_LISTENERS  128

/*
 * All flags that may be specified in parameter event_f_flags of fanotify_init.
 *
 * Internal and external open flags are stored together in field f_flags of
 * struct file. Only external open flags shall be allowed in event_f_flags.
 * Internal flags like FMODE_NONOTIFY, FMODE_EXEC, FMODE_NOCMTIME shall be
 * excluded.
 */
#define FANOTIFY_INIT_ALL_EVENT_F_BITS                          ( \
                O_ACCMODE       | O_APPEND      | O_NONBLOCK    | \
                __O_SYNC        | O_DSYNC       | O_CLOEXEC     | \
                O_LARGEFILE     | O_NOATIME     )

extern const struct fsnotify_ops fanotify_fsnotify_ops;

struct kmem_cache *fanotify_mark_cache __read_mostly;
struct kmem_cache *fanotify_event_cachep __read_mostly;
struct kmem_cache *fanotify_perm_event_cachep __read_mostly;

#define FANOTIFY_EVENT_ALIGN 4

static int fanotify_event_info_len(struct fanotify_event *event)
{
        if (!fanotify_event_has_fid(event))
                return 0;

        return roundup(sizeof(struct fanotify_event_info_fid) +
                       sizeof(struct file_handle) + event->fh_len,
                       FANOTIFY_EVENT_ALIGN);
}

/*
 * Get an fsnotify notification event if one exists and is small
 * enough to fit in "count". Return an error pointer if the count
 * is not large enough. When permission event is dequeued, its state is
 * updated accordingly.
 */
static struct fsnotify_event *get_one_event(struct fsnotify_group *group,
                                            size_t count)
{
        size_t event_size = FAN_EVENT_METADATA_LEN;
        struct fsnotify_event *fsn_event = NULL;

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

        spin_lock(&group->notification_lock);
        if (fsnotify_notify_queue_is_empty(group))
                goto out;

        if (FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
                event_size += fanotify_event_info_len(
                        FANOTIFY_E(fsnotify_peek_first_event(group)));
        }

        if (event_size > count) {
                fsn_event = ERR_PTR(-EINVAL);
                goto out;
        }
        fsn_event = fsnotify_remove_first_event(group);
        if (fanotify_is_perm_event(FANOTIFY_E(fsn_event)->mask))
                FANOTIFY_PE(fsn_event)->state = FAN_EVENT_REPORTED;
out:
        spin_unlock(&group->notification_lock);
        return fsn_event;
}

static int create_fd(struct fsnotify_group *group,
                     struct fanotify_event *event,
                     struct file **file)
{
        int client_fd;
        struct file *new_file;

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

        client_fd = get_unused_fd_flags(group->fanotify_data.f_flags);
        if (client_fd < 0)
                return client_fd;

        /*
         * we need a new file handle for the userspace program so it can read even if it was
         * originally opened O_WRONLY.
         */
        /* it's possible this event was an overflow event.  in that case dentry and mnt
         * are NULL;  That's fine, just don't call dentry open */
        if (event->path.dentry && event->path.mnt)
                new_file = dentry_open(&event->path,
                                       group->fanotify_data.f_flags | FMODE_NONOTIFY,
                                       current_cred());
        else
                new_file = ERR_PTR(-EOVERFLOW);
        if (IS_ERR(new_file)) {
                /*
                 * we still send an event even if we can't open the file.  this
                 * can happen when say tasks are gone and we try to open their
                 * /proc files or we try to open a WRONLY file like in sysfs
                 * we just send the errno to userspace since there isn't much
                 * else we can do.
                 */
                put_unused_fd(client_fd);
                client_fd = PTR_ERR(new_file);
        } else {
                *file = new_file;
        }

        return client_fd;
}

/*
 * Finish processing of permission event by setting it to ANSWERED state and
 * drop group->notification_lock.
 */
static void finish_permission_event(struct fsnotify_group *group,
                                    struct fanotify_perm_event *event,
                                    unsigned int response)
                                    __releases(&group->notification_lock)
{
        bool destroy = false;

        assert_spin_locked(&group->notification_lock);
        event->response = response;
        if (event->state == FAN_EVENT_CANCELED)
                destroy = true;
        else
                event->state = FAN_EVENT_ANSWERED;
        spin_unlock(&group->notification_lock);
        if (destroy)
                fsnotify_destroy_event(group, &event->fae.fse);
}

static int process_access_response(struct fsnotify_group *group,
                                   struct fanotify_response *response_struct)
{
        struct fanotify_perm_event *event;
        int fd = response_struct->fd;
        int response = response_struct->response;

        pr_debug("%s: group=%p fd=%d response=%d\n", __func__, group,
                 fd, response);
        /*
         * make sure the response is valid, if invalid we do nothing and either
         * userspace can send a valid response or we will clean it up after the
         * timeout
         */
        switch (response & ~FAN_AUDIT) {
        case FAN_ALLOW:
        case FAN_DENY:
                break;
        default:
                return -EINVAL;
        }

        if (fd < 0)
                return -EINVAL;

        if ((response & FAN_AUDIT) && !FAN_GROUP_FLAG(group, FAN_ENABLE_AUDIT))
                return -EINVAL;

        spin_lock(&group->notification_lock);
        list_for_each_entry(event, &group->fanotify_data.access_list,
                            fae.fse.list) {
                if (event->fd != fd)
                        continue;

                list_del_init(&event->fae.fse.list);
                finish_permission_event(group, event, response);
                wake_up(&group->fanotify_data.access_waitq);
                return 0;
        }
        spin_unlock(&group->notification_lock);

        return -ENOENT;
}

static int copy_fid_to_user(struct fanotify_event *event, char __user *buf)
{
        struct fanotify_event_info_fid info = { };
        struct file_handle handle = { };
        unsigned char bounce[FANOTIFY_INLINE_FH_LEN], *fh;
        size_t fh_len = event->fh_len;
        size_t len = fanotify_event_info_len(event);

        if (!len)
                return 0;

        if (WARN_ON_ONCE(len < sizeof(info) + sizeof(handle) + fh_len))
                return -EFAULT;

        /* Copy event info fid header followed by vaiable sized file handle */
        info.hdr.info_type = FAN_EVENT_INFO_TYPE_FID;
        info.hdr.len = len;
        info.fsid = event->fid.fsid;
        if (copy_to_user(buf, &info, sizeof(info)))
                return -EFAULT;

        buf += sizeof(info);
        len -= sizeof(info);
        handle.handle_type = event->fh_type;
        handle.handle_bytes = fh_len;
        if (copy_to_user(buf, &handle, sizeof(handle)))
                return -EFAULT;

        buf += sizeof(handle);
        len -= sizeof(handle);
        /*
         * For an inline fh, copy through stack to exclude the copy from
         * usercopy hardening protections.
         */
        fh = fanotify_event_fh(event);
        if (fh_len <= FANOTIFY_INLINE_FH_LEN) {
                memcpy(bounce, fh, fh_len);
                fh = bounce;
        }
        if (copy_to_user(buf, fh, fh_len))
                return -EFAULT;

        /* Pad with 0's */
        buf += fh_len;
        len -= fh_len;
        WARN_ON_ONCE(len < 0 || len >= FANOTIFY_EVENT_ALIGN);
        if (len > 0 && clear_user(buf, len))
                return -EFAULT;

        return 0;
}

static ssize_t copy_event_to_user(struct fsnotify_group *group,
                                  struct fsnotify_event *fsn_event,
                                  char __user *buf, size_t count)
{
        struct fanotify_event_metadata metadata;
        struct fanotify_event *event;
        struct file *f = NULL;
        int ret, fd = FAN_NOFD;

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

        event = container_of(fsn_event, struct fanotify_event, fse);
        metadata.event_len = FAN_EVENT_METADATA_LEN;
        metadata.metadata_len = FAN_EVENT_METADATA_LEN;
        metadata.vers = FANOTIFY_METADATA_VERSION;
        metadata.reserved = 0;
        metadata.mask = event->mask & FANOTIFY_OUTGOING_EVENTS;
        metadata.pid = pid_vnr(event->pid);

        if (fanotify_event_has_path(event)) {
                fd = create_fd(group, event, &f);
                if (fd < 0)
                        return fd;
        } else if (fanotify_event_has_fid(event)) {
                metadata.event_len += fanotify_event_info_len(event);
        }
        metadata.fd = fd;

        ret = -EFAULT;
        /*
         * Sanity check copy size in case get_one_event() and
         * fill_event_metadata() event_len sizes ever get out of sync.
         */
        if (WARN_ON_ONCE(metadata.event_len > count))
                goto out_close_fd;

        if (copy_to_user(buf, &metadata, FAN_EVENT_METADATA_LEN))
                goto out_close_fd;

        if (fanotify_is_perm_event(event->mask))
                FANOTIFY_PE(fsn_event)->fd = fd;

        if (fanotify_event_has_path(event)) {
                fd_install(fd, f);
        } else if (fanotify_event_has_fid(event)) {
                ret = copy_fid_to_user(event, buf + FAN_EVENT_METADATA_LEN);
                if (ret < 0)
                        return ret;
        }

        return metadata.event_len;

out_close_fd:
        if (fd != FAN_NOFD) {
                put_unused_fd(fd);
                fput(f);
        }
        return ret;
}

/* intofiy userspace file descriptor functions */
static __poll_t fanotify_poll(struct file *file, poll_table *wait)
{
        struct fsnotify_group *group = file->private_data;
        __poll_t ret = 0;

        poll_wait(file, &group->notification_waitq, wait);
        spin_lock(&group->notification_lock);
        if (!fsnotify_notify_queue_is_empty(group))
                ret = EPOLLIN | EPOLLRDNORM;
        spin_unlock(&group->notification_lock);

        return ret;
}

static ssize_t fanotify_read(struct file *file, char __user *buf,
                             size_t count, loff_t *pos)
{
        struct fsnotify_group *group;
        struct fsnotify_event *kevent;
        char __user *start;
        int ret;
        DEFINE_WAIT_FUNC(wait, woken_wake_function);

        start = buf;
        group = file->private_data;

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

        add_wait_queue(&group->notification_waitq, &wait);
        while (1) {
                kevent = get_one_event(group, count);
                if (IS_ERR(kevent)) {
                        ret = PTR_ERR(kevent);
                        break;
                }

                if (!kevent) {
                        ret = -EAGAIN;
                        if (file->f_flags & O_NONBLOCK)
                                break;

                        ret = -ERESTARTSYS;
                        if (signal_pending(current))
                                break;

                        if (start != buf)
                                break;

                        wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
                        continue;
                }

                ret = copy_event_to_user(group, kevent, buf, count);
                if (unlikely(ret == -EOPENSTALE)) {
                        /*
                         * We cannot report events with stale fd so drop it.
                         * Setting ret to 0 will continue the event loop and
                         * do the right thing if there are no more events to
                         * read (i.e. return bytes read, -EAGAIN or wait).
                         */
                        ret = 0;
                }

                /*
                 * Permission events get queued to wait for response.  Other
                 * events can be destroyed now.
                 */
                if (!fanotify_is_perm_event(FANOTIFY_E(kevent)->mask)) {
                        fsnotify_destroy_event(group, kevent);
                } else {
                        if (ret <= 0) {
                                spin_lock(&group->notification_lock);
                                finish_permission_event(group,
                                        FANOTIFY_PE(kevent), FAN_DENY);
                                wake_up(&group->fanotify_data.access_waitq);
                        } else {
                                spin_lock(&group->notification_lock);
                                list_add_tail(&kevent->list,
                                        &group->fanotify_data.access_list);
                                spin_unlock(&group->notification_lock);
                        }
                }
                if (ret < 0)
                        break;
                buf += ret;
                count -= ret;
        }
        remove_wait_queue(&group->notification_waitq, &wait);

        if (start != buf && ret != -EFAULT)
                ret = buf - start;
        return ret;
}

static ssize_t fanotify_write(struct file *file, const char __user *buf, size_t count, loff_t *pos)
{
        struct fanotify_response response = { .fd = -1, .response = -1 };
        struct fsnotify_group *group;
        int ret;

        if (!IS_ENABLED(CONFIG_FANOTIFY_ACCESS_PERMISSIONS))
                return -EINVAL;

        group = file->private_data;

        if (count > sizeof(response))
                count = sizeof(response);

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

        if (copy_from_user(&response, buf, count))
                return -EFAULT;

        ret = process_access_response(group, &response);
        if (ret < 0)
                count = ret;

        return count;
}

static int fanotify_release(struct inode *ignored, struct file *file)
{
        struct fsnotify_group *group = file->private_data;
        struct fanotify_perm_event *event;
        struct fsnotify_event *fsn_event;

        /*
         * Stop new events from arriving in the notification queue. since
         * userspace cannot use fanotify fd anymore, no event can enter or
         * leave access_list by now either.
         */
        fsnotify_group_stop_queueing(group);

        /*
         * Process all permission events on access_list and notification queue
         * and simulate reply from userspace.
         */
        spin_lock(&group->notification_lock);
        while (!list_empty(&group->fanotify_data.access_list)) {
                event = list_first_entry(&group->fanotify_data.access_list,
                                struct fanotify_perm_event, fae.fse.list);
                list_del_init(&event->fae.fse.list);
                finish_permission_event(group, event, FAN_ALLOW);
                spin_lock(&group->notification_lock);
        }

        /*
         * Destroy all non-permission events. For permission events just
         * dequeue them and set the response. They will be freed once the
         * response is consumed and fanotify_get_response() returns.
         */
        while (!fsnotify_notify_queue_is_empty(group)) {
                fsn_event = fsnotify_remove_first_event(group);
                if (!(FANOTIFY_E(fsn_event)->mask & FANOTIFY_PERM_EVENTS)) {
                        spin_unlock(&group->notification_lock);
                        fsnotify_destroy_event(group, fsn_event);
                } else {
                        finish_permission_event(group, FANOTIFY_PE(fsn_event),
                                                FAN_ALLOW);
                }
                spin_lock(&group->notification_lock);
        }
        spin_unlock(&group->notification_lock);

        /* Response for all permission events it set, wakeup waiters */
        wake_up(&group->fanotify_data.access_waitq);

        /* matches the fanotify_init->fsnotify_alloc_group */
        fsnotify_destroy_group(group);

        return 0;
}

static long fanotify_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
        struct fsnotify_group *group;
        struct fsnotify_event *fsn_event;
        void __user *p;
        int ret = -ENOTTY;
        size_t send_len = 0;

        group = file->private_data;

        p = (void __user *) arg;

        switch (cmd) {
        case FIONREAD:
                spin_lock(&group->notification_lock);
                list_for_each_entry(fsn_event, &group->notification_list, list)
                        send_len += FAN_EVENT_METADATA_LEN;
                spin_unlock(&group->notification_lock);
                ret = put_user(send_len, (int __user *) p);
                break;
        }

        return ret;
}

static const struct file_operations fanotify_fops = {
        .show_fdinfo    = fanotify_show_fdinfo,
        .poll           = fanotify_poll,
        .read           = fanotify_read,
        .write          = fanotify_write,
        .fasync         = NULL,
        .release        = fanotify_release,
        .unlocked_ioctl = fanotify_ioctl,
        .compat_ioctl   = compat_ptr_ioctl,
        .llseek         = noop_llseek,
};

static int fanotify_find_path(int dfd, const char __user *filename,
                              struct path *path, unsigned int flags, __u64 mask,
                              unsigned int obj_type)
{
        int ret;

        pr_debug("%s: dfd=%d filename=%p flags=%x\n", __func__,
                 dfd, filename, flags);

        if (filename == NULL) {
                struct fd f = fdget(dfd);

                ret = -EBADF;
                if (!f.file)
                        goto out;

                ret = -ENOTDIR;
                if ((flags & FAN_MARK_ONLYDIR) &&
                    !(S_ISDIR(file_inode(f.file)->i_mode))) {
                        fdput(f);
                        goto out;
                }

                *path = f.file->f_path;
                path_get(path);
                fdput(f);
        } else {
                unsigned int lookup_flags = 0;

                if (!(flags & FAN_MARK_DONT_FOLLOW))
                        lookup_flags |= LOOKUP_FOLLOW;
                if (flags & FAN_MARK_ONLYDIR)
                        lookup_flags |= LOOKUP_DIRECTORY;

                ret = user_path_at(dfd, filename, lookup_flags, path);
                if (ret)
                        goto out;
        }

        /* you can only watch an inode if you have read permissions on it */
        ret = inode_permission(path->dentry->d_inode, MAY_READ);
        if (ret) {
                path_put(path);
                goto out;
        }

        ret = security_path_notify(path, mask, obj_type);
        if (ret)
                path_put(path);

out:
        return ret;
}

static __u32 fanotify_mark_remove_from_mask(struct fsnotify_mark *fsn_mark,
                                            __u32 mask,
                                            unsigned int flags,
                                            int *destroy)
{
        __u32 oldmask = 0;

        spin_lock(&fsn_mark->lock);
        if (!(flags & FAN_MARK_IGNORED_MASK)) {
                oldmask = fsn_mark->mask;
                fsn_mark->mask &= ~mask;
        } else {
                fsn_mark->ignored_mask &= ~mask;
        }
        *destroy = !(fsn_mark->mask | fsn_mark->ignored_mask);
        spin_unlock(&fsn_mark->lock);

        return mask & oldmask;
}

static int fanotify_remove_mark(struct fsnotify_group *group,
                                fsnotify_connp_t *connp, __u32 mask,
                                unsigned int flags)
{
        struct fsnotify_mark *fsn_mark = NULL;
        __u32 removed;
        int destroy_mark;

        mutex_lock(&group->mark_mutex);
        fsn_mark = fsnotify_find_mark(connp, group);
        if (!fsn_mark) {
                mutex_unlock(&group->mark_mutex);
                return -ENOENT;
        }

        removed = fanotify_mark_remove_from_mask(fsn_mark, mask, flags,
                                                 &destroy_mark);
        if (removed & fsnotify_conn_mask(fsn_mark->connector))
                fsnotify_recalc_mask(fsn_mark->connector);
        if (destroy_mark)
                fsnotify_detach_mark(fsn_mark);
        mutex_unlock(&group->mark_mutex);
        if (destroy_mark)
                fsnotify_free_mark(fsn_mark);

        /* matches the fsnotify_find_mark() */
        fsnotify_put_mark(fsn_mark);
        return 0;
}

static int fanotify_remove_vfsmount_mark(struct fsnotify_group *group,
                                         struct vfsmount *mnt, __u32 mask,
                                         unsigned int flags)
{
        return fanotify_remove_mark(group, &real_mount(mnt)->mnt_fsnotify_marks,
                                    mask, flags);
}

static int fanotify_remove_sb_mark(struct fsnotify_group *group,
                                      struct super_block *sb, __u32 mask,
                                      unsigned int flags)
{
        return fanotify_remove_mark(group, &sb->s_fsnotify_marks, mask, flags);
}

static int fanotify_remove_inode_mark(struct fsnotify_group *group,
                                      struct inode *inode, __u32 mask,
                                      unsigned int flags)
{
        return fanotify_remove_mark(group, &inode->i_fsnotify_marks, mask,
                                    flags);
}

static __u32 fanotify_mark_add_to_mask(struct fsnotify_mark *fsn_mark,
                                       __u32 mask,
                                       unsigned int flags)
{
        __u32 oldmask = -1;

        spin_lock(&fsn_mark->lock);
        if (!(flags & FAN_MARK_IGNORED_MASK)) {
                oldmask = fsn_mark->mask;
                fsn_mark->mask |= mask;
        } else {
                fsn_mark->ignored_mask |= mask;
                if (flags & FAN_MARK_IGNORED_SURV_MODIFY)
                        fsn_mark->flags |= FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY;
        }
        spin_unlock(&fsn_mark->lock);

        return mask & ~oldmask;
}

static struct fsnotify_mark *fanotify_add_new_mark(struct fsnotify_group *group,
                                                   fsnotify_connp_t *connp,
                                                   unsigned int type,
                                                   __kernel_fsid_t *fsid)
{
        struct fsnotify_mark *mark;
        int ret;

        if (atomic_read(&group->num_marks) > group->fanotify_data.max_marks)
                return ERR_PTR(-ENOSPC);

        mark = kmem_cache_alloc(fanotify_mark_cache, GFP_KERNEL);
        if (!mark)
                return ERR_PTR(-ENOMEM);

        fsnotify_init_mark(mark, group);
        ret = fsnotify_add_mark_locked(mark, connp, type, 0, fsid);
        if (ret) {
                fsnotify_put_mark(mark);
                return ERR_PTR(ret);
        }

        return mark;
}


static int fanotify_add_mark(struct fsnotify_group *group,
                             fsnotify_connp_t *connp, unsigned int type,
                             __u32 mask, unsigned int flags,
                             __kernel_fsid_t *fsid)
{
        struct fsnotify_mark *fsn_mark;
        __u32 added;

        mutex_lock(&group->mark_mutex);
        fsn_mark = fsnotify_find_mark(connp, group);
        if (!fsn_mark) {
                fsn_mark = fanotify_add_new_mark(group, connp, type, fsid);
                if (IS_ERR(fsn_mark)) {
                        mutex_unlock(&group->mark_mutex);
                        return PTR_ERR(fsn_mark);
                }
        }
        added = fanotify_mark_add_to_mask(fsn_mark, mask, flags);
        if (added & ~fsnotify_conn_mask(fsn_mark->connector))
                fsnotify_recalc_mask(fsn_mark->connector);
        mutex_unlock(&group->mark_mutex);

        fsnotify_put_mark(fsn_mark);
        return 0;
}

static int fanotify_add_vfsmount_mark(struct fsnotify_group *group,
                                      struct vfsmount *mnt, __u32 mask,
                                      unsigned int flags, __kernel_fsid_t *fsid)
{
        return fanotify_add_mark(group, &real_mount(mnt)->mnt_fsnotify_marks,
                                 FSNOTIFY_OBJ_TYPE_VFSMOUNT, mask, flags, fsid);
}

static int fanotify_add_sb_mark(struct fsnotify_group *group,
                                struct super_block *sb, __u32 mask,
                                unsigned int flags, __kernel_fsid_t *fsid)
{
        return fanotify_add_mark(group, &sb->s_fsnotify_marks,
                                 FSNOTIFY_OBJ_TYPE_SB, mask, flags, fsid);
}

static int fanotify_add_inode_mark(struct fsnotify_group *group,
                                   struct inode *inode, __u32 mask,
                                   unsigned int flags, __kernel_fsid_t *fsid)
{
        pr_debug("%s: group=%p inode=%p\n", __func__, group, inode);

        /*
         * If some other task has this inode open for write we should not add
         * an ignored mark, unless that ignored mark is supposed to survive
         * modification changes anyway.
         */
        if ((flags & FAN_MARK_IGNORED_MASK) &&
            !(flags & FAN_MARK_IGNORED_SURV_MODIFY) &&
            inode_is_open_for_write(inode))
                return 0;

        return fanotify_add_mark(group, &inode->i_fsnotify_marks,
                                 FSNOTIFY_OBJ_TYPE_INODE, mask, flags, fsid);
}

/* fanotify syscalls */
SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
{
        struct fsnotify_group *group;
        int f_flags, fd;
        struct user_struct *user;
        struct fanotify_event *oevent;

        pr_debug("%s: flags=%x event_f_flags=%x\n",
                 __func__, flags, event_f_flags);

        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

#ifdef CONFIG_AUDITSYSCALL
        if (flags & ~(FANOTIFY_INIT_FLAGS | FAN_ENABLE_AUDIT))
#else
        if (flags & ~FANOTIFY_INIT_FLAGS)
#endif
                return -EINVAL;

        if (event_f_flags & ~FANOTIFY_INIT_ALL_EVENT_F_BITS)
                return -EINVAL;

        switch (event_f_flags & O_ACCMODE) {
        case O_RDONLY:
        case O_RDWR:
        case O_WRONLY:
                break;
        default:
                return -EINVAL;
        }

        if ((flags & FAN_REPORT_FID) &&
            (flags & FANOTIFY_CLASS_BITS) != FAN_CLASS_NOTIF)
                return -EINVAL;

        user = get_current_user();
        if (atomic_read(&user->fanotify_listeners) > FANOTIFY_DEFAULT_MAX_LISTENERS) {
                free_uid(user);
                return -EMFILE;
        }

        f_flags = O_RDWR | FMODE_NONOTIFY;
        if (flags & FAN_CLOEXEC)
                f_flags |= O_CLOEXEC;
        if (flags & FAN_NONBLOCK)
                f_flags |= O_NONBLOCK;

        /* fsnotify_alloc_group takes a ref.  Dropped in fanotify_release */
        group = fsnotify_alloc_group(&fanotify_fsnotify_ops);
        if (IS_ERR(group)) {
                free_uid(user);
                return PTR_ERR(group);
        }

        group->fanotify_data.user = user;
        group->fanotify_data.flags = flags;
        atomic_inc(&user->fanotify_listeners);
        group->memcg = get_mem_cgroup_from_mm(current->mm);

        oevent = fanotify_alloc_event(group, NULL, FS_Q_OVERFLOW, NULL,
                                      FSNOTIFY_EVENT_NONE, NULL);
        if (unlikely(!oevent)) {
                fd = -ENOMEM;
                goto out_destroy_group;
        }
        group->overflow_event = &oevent->fse;

        if (force_o_largefile())
                event_f_flags |= O_LARGEFILE;
        group->fanotify_data.f_flags = event_f_flags;
        init_waitqueue_head(&group->fanotify_data.access_waitq);
        INIT_LIST_HEAD(&group->fanotify_data.access_list);
        switch (flags & FANOTIFY_CLASS_BITS) {
        case FAN_CLASS_NOTIF:
                group->priority = FS_PRIO_0;
                break;
        case FAN_CLASS_CONTENT:
                group->priority = FS_PRIO_1;
                break;
        case FAN_CLASS_PRE_CONTENT:
                group->priority = FS_PRIO_2;
                break;
        default:
                fd = -EINVAL;
                goto out_destroy_group;
        }

        if (flags & FAN_UNLIMITED_QUEUE) {
                fd = -EPERM;
                if (!capable(CAP_SYS_ADMIN))
                        goto out_destroy_group;
                group->max_events = UINT_MAX;
        } else {
                group->max_events = FANOTIFY_DEFAULT_MAX_EVENTS;
        }

        if (flags & FAN_UNLIMITED_MARKS) {
                fd = -EPERM;
                if (!capable(CAP_SYS_ADMIN))
                        goto out_destroy_group;
                group->fanotify_data.max_marks = UINT_MAX;
        } else {
                group->fanotify_data.max_marks = FANOTIFY_DEFAULT_MAX_MARKS;
        }

        if (flags & FAN_ENABLE_AUDIT) {
                fd = -EPERM;
                if (!capable(CAP_AUDIT_WRITE))
                        goto out_destroy_group;
        }

        fd = anon_inode_getfd("[fanotify]", &fanotify_fops, group, f_flags);
        if (fd < 0)
                goto out_destroy_group;

        return fd;

out_destroy_group:
        fsnotify_destroy_group(group);
        return fd;
}

/* Check if filesystem can encode a unique fid */
static int fanotify_test_fid(struct path *path, __kernel_fsid_t *fsid)
{
        __kernel_fsid_t root_fsid;
        int err;

        /*
         * Make sure path is not in filesystem with zero fsid (e.g. tmpfs).
         */
        err = vfs_get_fsid(path->dentry, fsid);
        if (err)
                return err;

        if (!fsid->val[0] && !fsid->val[1])
                return -ENODEV;

        /*
         * Make sure path is not inside a filesystem subvolume (e.g. btrfs)
         * which uses a different fsid than sb root.
         */
        err = vfs_get_fsid(path->dentry->d_sb->s_root, &root_fsid);
        if (err)
                return err;

        if (root_fsid.val[0] != fsid->val[0] ||
            root_fsid.val[1] != fsid->val[1])
                return -EXDEV;

        /*
         * We need to make sure that the file system supports at least
         * encoding a file handle so user can use name_to_handle_at() to
         * compare fid returned with event to the file handle of watched
         * objects. However, name_to_handle_at() requires that the
         * filesystem also supports decoding file handles.
         */
        if (!path->dentry->d_sb->s_export_op ||
            !path->dentry->d_sb->s_export_op->fh_to_dentry)
                return -EOPNOTSUPP;

        return 0;
}

static int fanotify_events_supported(struct path *path, __u64 mask)
{
        /*
         * Some filesystems such as 'proc' acquire unusual locks when opening
         * files. For them fanotify permission events have high chances of
         * deadlocking the system - open done when reporting fanotify event
         * blocks on this "unusual" lock while another process holding the lock
         * waits for fanotify permission event to be answered. Just disallow
         * permission events for such filesystems.
         */
        if (mask & FANOTIFY_PERM_EVENTS &&
            path->mnt->mnt_sb->s_type->fs_flags & FS_DISALLOW_NOTIFY_PERM)
                return -EINVAL;
        return 0;
}

static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
                            int dfd, const char  __user *pathname)
{
        struct inode *inode = NULL;
        struct vfsmount *mnt = NULL;
        struct fsnotify_group *group;
        struct fd f;
        struct path path;
        __kernel_fsid_t __fsid, *fsid = NULL;
        u32 valid_mask = FANOTIFY_EVENTS | FANOTIFY_EVENT_FLAGS;
        unsigned int mark_type = flags & FANOTIFY_MARK_TYPE_BITS;
        unsigned int obj_type;
        int ret;

        pr_debug("%s: fanotify_fd=%d flags=%x dfd=%d pathname=%p mask=%llx\n",
                 __func__, fanotify_fd, flags, dfd, pathname, mask);

        /* we only use the lower 32 bits as of right now. */
        if (mask & ((__u64)0xffffffff << 32))
                return -EINVAL;

        if (flags & ~FANOTIFY_MARK_FLAGS)
                return -EINVAL;

        switch (mark_type) {
        case FAN_MARK_INODE:
                obj_type = FSNOTIFY_OBJ_TYPE_INODE;
                break;
        case FAN_MARK_MOUNT:
                obj_type = FSNOTIFY_OBJ_TYPE_VFSMOUNT;
                break;
        case FAN_MARK_FILESYSTEM:
                obj_type = FSNOTIFY_OBJ_TYPE_SB;
                break;
        default:
                return -EINVAL;
        }

        switch (flags & (FAN_MARK_ADD | FAN_MARK_REMOVE | FAN_MARK_FLUSH)) {
        case FAN_MARK_ADD:              /* fallthrough */
        case FAN_MARK_REMOVE:
                if (!mask)
                        return -EINVAL;
                break;
        case FAN_MARK_FLUSH:
                if (flags & ~(FANOTIFY_MARK_TYPE_BITS | FAN_MARK_FLUSH))
                        return -EINVAL;
                break;
        default:
                return -EINVAL;
        }

        if (IS_ENABLED(CONFIG_FANOTIFY_ACCESS_PERMISSIONS))
                valid_mask |= FANOTIFY_PERM_EVENTS;

        if (mask & ~valid_mask)
                return -EINVAL;

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

        /* verify that this is indeed an fanotify instance */
        ret = -EINVAL;
        if (unlikely(f.file->f_op != &fanotify_fops))
                goto fput_and_out;
        group = f.file->private_data;

        /*
         * group->priority == FS_PRIO_0 == FAN_CLASS_NOTIF.  These are not
         * allowed to set permissions events.
         */
        ret = -EINVAL;
        if (mask & FANOTIFY_PERM_EVENTS &&
            group->priority == FS_PRIO_0)
                goto fput_and_out;

        /*
         * Events with data type inode do not carry enough information to report
         * event->fd, so we do not allow setting a mask for inode events unless
         * group supports reporting fid.
         * inode events are not supported on a mount mark, because they do not
         * carry enough information (i.e. path) to be filtered by mount point.
         */
        if (mask & FANOTIFY_INODE_EVENTS &&
            (!FAN_GROUP_FLAG(group, FAN_REPORT_FID) ||
             mark_type == FAN_MARK_MOUNT))
                goto fput_and_out;

        if (flags & FAN_MARK_FLUSH) {
                ret = 0;
                if (mark_type == FAN_MARK_MOUNT)
                        fsnotify_clear_vfsmount_marks_by_group(group);
                else if (mark_type == FAN_MARK_FILESYSTEM)
                        fsnotify_clear_sb_marks_by_group(group);
                else
                        fsnotify_clear_inode_marks_by_group(group);
                goto fput_and_out;
        }

        ret = fanotify_find_path(dfd, pathname, &path, flags,
                        (mask & ALL_FSNOTIFY_EVENTS), obj_type);
        if (ret)
                goto fput_and_out;

        if (flags & FAN_MARK_ADD) {
                ret = fanotify_events_supported(&path, mask);
                if (ret)
                        goto path_put_and_out;
        }

        if (FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
                ret = fanotify_test_fid(&path, &__fsid);
                if (ret)
                        goto path_put_and_out;

                fsid = &__fsid;
        }

        /* inode held in place by reference to path; group by fget on fd */
        if (mark_type == FAN_MARK_INODE)
                inode = path.dentry->d_inode;
        else
                mnt = path.mnt;

        /* create/update an inode mark */
        switch (flags & (FAN_MARK_ADD | FAN_MARK_REMOVE)) {
        case FAN_MARK_ADD:
                if (mark_type == FAN_MARK_MOUNT)
                        ret = fanotify_add_vfsmount_mark(group, mnt, mask,
                                                         flags, fsid);
                else if (mark_type == FAN_MARK_FILESYSTEM)
                        ret = fanotify_add_sb_mark(group, mnt->mnt_sb, mask,
                                                   flags, fsid);
                else
                        ret = fanotify_add_inode_mark(group, inode, mask,
                                                      flags, fsid);
                break;
        case FAN_MARK_REMOVE:
                if (mark_type == FAN_MARK_MOUNT)
                        ret = fanotify_remove_vfsmount_mark(group, mnt, mask,
                                                            flags);
                else if (mark_type == FAN_MARK_FILESYSTEM)
                        ret = fanotify_remove_sb_mark(group, mnt->mnt_sb, mask,
                                                      flags);
                else
                        ret = fanotify_remove_inode_mark(group, inode, mask,
                                                         flags);
                break;
        default:
                ret = -EINVAL;
        }

path_put_and_out:
        path_put(&path);
fput_and_out:
        fdput(f);
        return ret;
}

SYSCALL_DEFINE5(fanotify_mark, int, fanotify_fd, unsigned int, flags,
                              __u64, mask, int, dfd,
                              const char  __user *, pathname)
{
        return do_fanotify_mark(fanotify_fd, flags, mask, dfd, pathname);
}

#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE6(fanotify_mark,
                                int, fanotify_fd, unsigned int, flags,
                                __u32, mask0, __u32, mask1, int, dfd,
                                const char  __user *, pathname)
{
        return do_fanotify_mark(fanotify_fd, flags,
#ifdef __BIG_ENDIAN
                                ((__u64)mask0 << 32) | mask1,
#else
                                ((__u64)mask1 << 32) | mask0,
#endif
                                 dfd, pathname);
}
#endif

/*
 * fanotify_user_setup - Our initialization function.  Note that we cannot return
 * error because we have compiled-in VFS hooks.  So an (unlikely) failure here
 * must result in panic().
 */
static int __init fanotify_user_setup(void)
{
        BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 8);
        BUILD_BUG_ON(HWEIGHT32(FANOTIFY_MARK_FLAGS) != 9);

        fanotify_mark_cache = KMEM_CACHE(fsnotify_mark,
                                         SLAB_PANIC|SLAB_ACCOUNT);
        fanotify_event_cachep = KMEM_CACHE(fanotify_event, SLAB_PANIC);
        if (IS_ENABLED(CONFIG_FANOTIFY_ACCESS_PERMISSIONS)) {
                fanotify_perm_event_cachep =
                        KMEM_CACHE(fanotify_perm_event, SLAB_PANIC);
        }

        return 0;
}
device_initcall(fanotify_user_setup);