// SPDX-License-Identifier: GPL-2.0
#include <linux/fanotify.h>
#include <linux/fcntl.h>
#include <linux/fdtable.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_OLD_DEFAULT_MAX_MARKS  8192
#define FANOTIFY_DEFAULT_MAX_GROUPS     128
#define FANOTIFY_DEFAULT_FEE_POOL_SIZE  32

/*
 * Legacy fanotify marks limits (8192) is per group and we introduced a tunable
 * limit of marks per user, similar to inotify.  Effectively, the legacy limit
 * of fanotify marks per user is <max marks per group> * <max groups per user>.
 * This default limit (1M) also happens to match the increased limit of inotify
 * max_user_watches since v5.10.
 */
#define FANOTIFY_DEFAULT_MAX_USER_MARKS \
        (FANOTIFY_OLD_DEFAULT_MAX_MARKS * FANOTIFY_DEFAULT_MAX_GROUPS)

/*
 * Most of the memory cost of adding an inode mark is pinning the marked inode.
 * The size of the filesystem inode struct is not uniform across filesystems,
 * so double the size of a VFS inode is used as a conservative approximation.
 */
#define INODE_MARK_COST (2 * sizeof(struct inode))

/* configurable via /proc/sys/fs/fanotify/ */
static int fanotify_max_queued_events __read_mostly;

#ifdef CONFIG_SYSCTL

#include <linux/sysctl.h>

static long ft_zero = 0;
static long ft_int_max = INT_MAX;

static struct ctl_table fanotify_table[] = {
        {
                .procname       = "max_user_groups",
                .data   = &init_user_ns.ucount_max[UCOUNT_FANOTIFY_GROUPS],
                .maxlen         = sizeof(long),
                .mode           = 0644,
                .proc_handler   = proc_doulongvec_minmax,
                .extra1         = &ft_zero,
                .extra2         = &ft_int_max,
        },
        {
                .procname       = "max_user_marks",
                .data   = &init_user_ns.ucount_max[UCOUNT_FANOTIFY_MARKS],
                .maxlen         = sizeof(long),
                .mode           = 0644,
                .proc_handler   = proc_doulongvec_minmax,
                .extra1         = &ft_zero,
                .extra2         = &ft_int_max,
        },
        {
                .procname       = "max_queued_events",
                .data           = &fanotify_max_queued_events,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = SYSCTL_ZERO
        },
        { }
};

static void __init fanotify_sysctls_init(void)
{
        register_sysctl("fs/fanotify", fanotify_table);
}
#else
#define fanotify_sysctls_init() do { } while (0)
#endif /* CONFIG_SYSCTL */

/*
 * 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_fid_event_cachep __read_mostly;
struct kmem_cache *fanotify_path_event_cachep __read_mostly;
struct kmem_cache *fanotify_perm_event_cachep __read_mostly;

#define FANOTIFY_EVENT_ALIGN 4
#define FANOTIFY_FID_INFO_HDR_LEN \
        (sizeof(struct fanotify_event_info_fid) + sizeof(struct file_handle))
#define FANOTIFY_PIDFD_INFO_HDR_LEN \
        sizeof(struct fanotify_event_info_pidfd)
#define FANOTIFY_ERROR_INFO_LEN \
        (sizeof(struct fanotify_event_info_error))

static int fanotify_fid_info_len(int fh_len, int name_len)
{
        int info_len = fh_len;

        if (name_len)
                info_len += name_len + 1;

        return roundup(FANOTIFY_FID_INFO_HDR_LEN + info_len,
                       FANOTIFY_EVENT_ALIGN);
}

/* FAN_RENAME may have one or two dir+name info records */
static int fanotify_dir_name_info_len(struct fanotify_event *event)
{
        struct fanotify_info *info = fanotify_event_info(event);
        int dir_fh_len = fanotify_event_dir_fh_len(event);
        int dir2_fh_len = fanotify_event_dir2_fh_len(event);
        int info_len = 0;

        if (dir_fh_len)
                info_len += fanotify_fid_info_len(dir_fh_len,
                                                  info->name_len);
        if (dir2_fh_len)
                info_len += fanotify_fid_info_len(dir2_fh_len,
                                                  info->name2_len);

        return info_len;
}

static size_t fanotify_event_len(unsigned int info_mode,
                                 struct fanotify_event *event)
{
        size_t event_len = FAN_EVENT_METADATA_LEN;
        int fh_len;
        int dot_len = 0;

        if (!info_mode)
                return event_len;

        if (fanotify_is_error_event(event->mask))
                event_len += FANOTIFY_ERROR_INFO_LEN;

        if (fanotify_event_has_any_dir_fh(event)) {
                event_len += fanotify_dir_name_info_len(event);
        } else if ((info_mode & FAN_REPORT_NAME) &&
                   (event->mask & FAN_ONDIR)) {
                /*
                 * With group flag FAN_REPORT_NAME, if name was not recorded in
                 * event on a directory, we will report the name ".".
                 */
                dot_len = 1;
        }

        if (info_mode & FAN_REPORT_PIDFD)
                event_len += FANOTIFY_PIDFD_INFO_HDR_LEN;

        if (fanotify_event_has_object_fh(event)) {
                fh_len = fanotify_event_object_fh_len(event);
                event_len += fanotify_fid_info_len(fh_len, dot_len);
        }

        return event_len;
}

/*
 * Remove an hashed event from merge hash table.
 */
static void fanotify_unhash_event(struct fsnotify_group *group,
                                  struct fanotify_event *event)
{
        assert_spin_locked(&group->notification_lock);

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

        if (WARN_ON_ONCE(hlist_unhashed(&event->merge_list)))
                return;

        hlist_del_init(&event->merge_list);
}

/*
 * Get an fanotify 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 fanotify_event *get_one_event(struct fsnotify_group *group,
                                            size_t count)
{
        size_t event_size;
        struct fanotify_event *event = NULL;
        struct fsnotify_event *fsn_event;
        unsigned int info_mode = FAN_GROUP_FLAG(group, FANOTIFY_INFO_MODES);

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

        spin_lock(&group->notification_lock);
        fsn_event = fsnotify_peek_first_event(group);
        if (!fsn_event)
                goto out;

        event = FANOTIFY_E(fsn_event);
        event_size = fanotify_event_len(info_mode, event);

        if (event_size > count) {
                event = ERR_PTR(-EINVAL);
                goto out;
        }

        /*
         * Held the notification_lock the whole time, so this is the
         * same event we peeked above.
         */
        fsnotify_remove_first_event(group);
        if (fanotify_is_perm_event(event->mask))
                FANOTIFY_PERM(event)->state = FAN_EVENT_REPORTED;
        if (fanotify_is_hashed_event(event->mask))
                fanotify_unhash_event(group, event);
out:
        spin_unlock(&group->notification_lock);
        return event;
}

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

        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.
         */
        new_file = dentry_open(path,
                               group->fanotify_data.f_flags | __FMODE_NONOTIFY,
                               current_cred());
        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 size_t copy_error_info_to_user(struct fanotify_event *event,
                                      char __user *buf, int count)
{
        struct fanotify_event_info_error info = { };
        struct fanotify_error_event *fee = FANOTIFY_EE(event);

        info.hdr.info_type = FAN_EVENT_INFO_TYPE_ERROR;
        info.hdr.len = FANOTIFY_ERROR_INFO_LEN;

        if (WARN_ON(count < info.hdr.len))
                return -EFAULT;

        info.error = fee->error;
        info.error_count = fee->err_count;

        if (copy_to_user(buf, &info, sizeof(info)))
                return -EFAULT;

        return info.hdr.len;
}

static int copy_fid_info_to_user(__kernel_fsid_t *fsid, struct fanotify_fh *fh,
                                 int info_type, const char *name,
                                 size_t name_len,
                                 char __user *buf, size_t count)
{
        struct fanotify_event_info_fid info = { };
        struct file_handle handle = { };
        unsigned char bounce[FANOTIFY_INLINE_FH_LEN], *fh_buf;
        size_t fh_len = fh ? fh->len : 0;
        size_t info_len = fanotify_fid_info_len(fh_len, name_len);
        size_t len = info_len;

        pr_debug("%s: fh_len=%zu name_len=%zu, info_len=%zu, count=%zu\n",
                 __func__, fh_len, name_len, info_len, count);

        if (WARN_ON_ONCE(len < sizeof(info) || len > count))
                return -EFAULT;

        /*
         * Copy event info fid header followed by variable sized file handle
         * and optionally followed by variable sized filename.
         */
        switch (info_type) {
        case FAN_EVENT_INFO_TYPE_FID:
        case FAN_EVENT_INFO_TYPE_DFID:
                if (WARN_ON_ONCE(name_len))
                        return -EFAULT;
                break;
        case FAN_EVENT_INFO_TYPE_DFID_NAME:
        case FAN_EVENT_INFO_TYPE_OLD_DFID_NAME:
        case FAN_EVENT_INFO_TYPE_NEW_DFID_NAME:
                if (WARN_ON_ONCE(!name || !name_len))
                        return -EFAULT;
                break;
        default:
                return -EFAULT;
        }

        info.hdr.info_type = info_type;
        info.hdr.len = len;
        info.fsid = *fsid;
        if (copy_to_user(buf, &info, sizeof(info)))
                return -EFAULT;

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

        handle.handle_type = fh->type;
        handle.handle_bytes = fh_len;

        /* Mangle handle_type for bad file_handle */
        if (!fh_len)
                handle.handle_type = FILEID_INVALID;

        if (copy_to_user(buf, &handle, sizeof(handle)))
                return -EFAULT;

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

        /*
         * For an inline fh and inline file name, copy through stack to exclude
         * the copy from usercopy hardening protections.
         */
        fh_buf = fanotify_fh_buf(fh);
        if (fh_len <= FANOTIFY_INLINE_FH_LEN) {
                memcpy(bounce, fh_buf, fh_len);
                fh_buf = bounce;
        }
        if (copy_to_user(buf, fh_buf, fh_len))
                return -EFAULT;

        buf += fh_len;
        len -= fh_len;

        if (name_len) {
                /* Copy the filename with terminating null */
                name_len++;
                if (WARN_ON_ONCE(len < name_len))
                        return -EFAULT;

                if (copy_to_user(buf, name, name_len))
                        return -EFAULT;

                buf += name_len;
                len -= name_len;
        }

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

        return info_len;
}

static int copy_pidfd_info_to_user(int pidfd,
                                   char __user *buf,
                                   size_t count)
{
        struct fanotify_event_info_pidfd info = { };
        size_t info_len = FANOTIFY_PIDFD_INFO_HDR_LEN;

        if (WARN_ON_ONCE(info_len > count))
                return -EFAULT;

        info.hdr.info_type = FAN_EVENT_INFO_TYPE_PIDFD;
        info.hdr.len = info_len;
        info.pidfd = pidfd;

        if (copy_to_user(buf, &info, info_len))
                return -EFAULT;

        return info_len;
}

static int copy_info_records_to_user(struct fanotify_event *event,
                                     struct fanotify_info *info,
                                     unsigned int info_mode, int pidfd,
                                     char __user *buf, size_t count)
{
        int ret, total_bytes = 0, info_type = 0;
        unsigned int fid_mode = info_mode & FANOTIFY_FID_BITS;
        unsigned int pidfd_mode = info_mode & FAN_REPORT_PIDFD;

        /*
         * Event info records order is as follows:
         * 1. dir fid + name
         * 2. (optional) new dir fid + new name
         * 3. (optional) child fid
         */
        if (fanotify_event_has_dir_fh(event)) {
                info_type = info->name_len ? FAN_EVENT_INFO_TYPE_DFID_NAME :
                                             FAN_EVENT_INFO_TYPE_DFID;

                /* FAN_RENAME uses special info types */
                if (event->mask & FAN_RENAME)
                        info_type = FAN_EVENT_INFO_TYPE_OLD_DFID_NAME;

                ret = copy_fid_info_to_user(fanotify_event_fsid(event),
                                            fanotify_info_dir_fh(info),
                                            info_type,
                                            fanotify_info_name(info),
                                            info->name_len, buf, count);
                if (ret < 0)
                        return ret;

                buf += ret;
                count -= ret;
                total_bytes += ret;
        }

        /* New dir fid+name may be reported in addition to old dir fid+name */
        if (fanotify_event_has_dir2_fh(event)) {
                info_type = FAN_EVENT_INFO_TYPE_NEW_DFID_NAME;
                ret = copy_fid_info_to_user(fanotify_event_fsid(event),
                                            fanotify_info_dir2_fh(info),
                                            info_type,
                                            fanotify_info_name2(info),
                                            info->name2_len, buf, count);
                if (ret < 0)
                        return ret;

                buf += ret;
                count -= ret;
                total_bytes += ret;
        }

        if (fanotify_event_has_object_fh(event)) {
                const char *dot = NULL;
                int dot_len = 0;

                if (fid_mode == FAN_REPORT_FID || info_type) {
                        /*
                         * With only group flag FAN_REPORT_FID only type FID is
                         * reported. Second info record type is always FID.
                         */
                        info_type = FAN_EVENT_INFO_TYPE_FID;
                } else if ((fid_mode & FAN_REPORT_NAME) &&
                           (event->mask & FAN_ONDIR)) {
                        /*
                         * With group flag FAN_REPORT_NAME, if name was not
                         * recorded in an event on a directory, report the name
                         * "." with info type DFID_NAME.
                         */
                        info_type = FAN_EVENT_INFO_TYPE_DFID_NAME;
                        dot = ".";
                        dot_len = 1;
                } else if ((event->mask & ALL_FSNOTIFY_DIRENT_EVENTS) ||
                           (event->mask & FAN_ONDIR)) {
                        /*
                         * With group flag FAN_REPORT_DIR_FID, a single info
                         * record has type DFID for directory entry modification
                         * event and for event on a directory.
                         */
                        info_type = FAN_EVENT_INFO_TYPE_DFID;
                } else {
                        /*
                         * With group flags FAN_REPORT_DIR_FID|FAN_REPORT_FID,
                         * a single info record has type FID for event on a
                         * non-directory, when there is no directory to report.
                         * For example, on FAN_DELETE_SELF event.
                         */
                        info_type = FAN_EVENT_INFO_TYPE_FID;
                }

                ret = copy_fid_info_to_user(fanotify_event_fsid(event),
                                            fanotify_event_object_fh(event),
                                            info_type, dot, dot_len,
                                            buf, count);
                if (ret < 0)
                        return ret;

                buf += ret;
                count -= ret;
                total_bytes += ret;
        }

        if (pidfd_mode) {
                ret = copy_pidfd_info_to_user(pidfd, buf, count);
                if (ret < 0)
                        return ret;

                buf += ret;
                count -= ret;
                total_bytes += ret;
        }

        if (fanotify_is_error_event(event->mask)) {
                ret = copy_error_info_to_user(event, buf, count);
                if (ret < 0)
                        return ret;
                buf += ret;
                count -= ret;
                total_bytes += ret;
        }

        return total_bytes;
}

static ssize_t copy_event_to_user(struct fsnotify_group *group,
                                  struct fanotify_event *event,
                                  char __user *buf, size_t count)
{
        struct fanotify_event_metadata metadata;
        struct path *path = fanotify_event_path(event);
        struct fanotify_info *info = fanotify_event_info(event);
        unsigned int info_mode = FAN_GROUP_FLAG(group, FANOTIFY_INFO_MODES);
        unsigned int pidfd_mode = info_mode & FAN_REPORT_PIDFD;
        struct file *f = NULL;
        int ret, pidfd = FAN_NOPIDFD, fd = FAN_NOFD;

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

        metadata.event_len = fanotify_event_len(info_mode, event);
        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);
        /*
         * For an unprivileged listener, event->pid can be used to identify the
         * events generated by the listener process itself, without disclosing
         * the pids of other processes.
         */
        if (FAN_GROUP_FLAG(group, FANOTIFY_UNPRIV) &&
            task_tgid(current) != event->pid)
                metadata.pid = 0;

        /*
         * For now, fid mode is required for an unprivileged listener and
         * fid mode does not report fd in events.  Keep this check anyway
         * for safety in case fid mode requirement is relaxed in the future
         * to allow unprivileged listener to get events with no fd and no fid.
         */
        if (!FAN_GROUP_FLAG(group, FANOTIFY_UNPRIV) &&
            path && path->mnt && path->dentry) {
                fd = create_fd(group, path, &f);
                if (fd < 0)
                        return fd;
        }
        metadata.fd = fd;

        if (pidfd_mode) {
                /*
                 * Complain if the FAN_REPORT_PIDFD and FAN_REPORT_TID mutual
                 * exclusion is ever lifted. At the time of incoporating pidfd
                 * support within fanotify, the pidfd API only supported the
                 * creation of pidfds for thread-group leaders.
                 */
                WARN_ON_ONCE(FAN_GROUP_FLAG(group, FAN_REPORT_TID));

                /*
                 * The PIDTYPE_TGID check for an event->pid is performed
                 * preemptively in an attempt to catch out cases where the event
                 * listener reads events after the event generating process has
                 * already terminated. Report FAN_NOPIDFD to the event listener
                 * in those cases, with all other pidfd creation errors being
                 * reported as FAN_EPIDFD.
                 */
                if (metadata.pid == 0 ||
                    !pid_has_task(event->pid, PIDTYPE_TGID)) {
                        pidfd = FAN_NOPIDFD;
                } else {
                        pidfd = pidfd_create(event->pid, 0);
                        if (pidfd < 0)
                                pidfd = FAN_EPIDFD;
                }
        }

        ret = -EFAULT;
        /*
         * Sanity check copy size in case get_one_event() and
         * 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;

        buf += FAN_EVENT_METADATA_LEN;
        count -= FAN_EVENT_METADATA_LEN;

        if (fanotify_is_perm_event(event->mask))
                FANOTIFY_PERM(event)->fd = fd;

        if (info_mode) {
                ret = copy_info_records_to_user(event, info, info_mode, pidfd,
                                                buf, count);
                if (ret < 0)
                        goto out_close_fd;
        }

        if (f)
                fd_install(fd, f);

        return metadata.event_len;

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

        if (pidfd >= 0)
                close_fd(pidfd);

        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 fanotify_event *event;
        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) {
                /*
                 * User can supply arbitrarily large buffer. Avoid softlockups
                 * in case there are lots of available events.
                 */
                cond_resched();
                event = get_one_event(group, count);
                if (IS_ERR(event)) {
                        ret = PTR_ERR(event);
                        break;
                }

                if (!event) {
                        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, event, 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(event->mask)) {
                        fsnotify_destroy_event(group, &event->fse);
                } else {
                        if (ret <= 0) {
                                spin_lock(&group->notification_lock);
                                finish_permission_event(group,
                                        FANOTIFY_PERM(event), FAN_DENY);
                                wake_up(&group->fanotify_data.access_waitq);
                        } else {
                                spin_lock(&group->notification_lock);
                                list_add_tail(&event->fse.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))
                return -EINVAL;

        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 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)) {
                struct fanotify_perm_event *event;

                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 ((fsn_event = fsnotify_remove_first_event(group))) {
                struct fanotify_event *event = FANOTIFY_E(fsn_event);

                if (!(event->mask & FANOTIFY_PERM_EVENTS)) {
                        spin_unlock(&group->notification_lock);
                        fsnotify_destroy_event(group, fsn_event);
                } else {
                        finish_permission_event(group, FANOTIFY_PERM(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 = path_permission(path, 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,
                                            __u32 umask, int *destroy)
{
        __u32 oldmask, newmask;

        /* umask bits cannot be removed by user */
        mask &= ~umask;
        spin_lock(&fsn_mark->lock);
        oldmask = fsnotify_calc_mask(fsn_mark);
        if (!(flags & FAN_MARK_IGNORED_MASK)) {
                fsn_mark->mask &= ~mask;
        } else {
                fsn_mark->ignored_mask &= ~mask;
        }
        newmask = fsnotify_calc_mask(fsn_mark);
        /*
         * We need to keep the mark around even if remaining mask cannot
         * result in any events (e.g. mask == FAN_ONDIR) to support incremenal
         * changes to the mask.
         * Destroy mark when only umask bits remain.
         */
        *destroy = !((fsn_mark->mask | fsn_mark->ignored_mask) & ~umask);
        spin_unlock(&fsn_mark->lock);

        return oldmask & ~newmask;
}

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

        fsnotify_group_lock(group);
        fsn_mark = fsnotify_find_mark(connp, group);
        if (!fsn_mark) {
                fsnotify_group_unlock(group);
                return -ENOENT;
        }

        removed = fanotify_mark_remove_from_mask(fsn_mark, mask, flags,
                                                 umask, &destroy_mark);
        if (removed & fsnotify_conn_mask(fsn_mark->connector))
                fsnotify_recalc_mask(fsn_mark->connector);
        if (destroy_mark)
                fsnotify_detach_mark(fsn_mark);
        fsnotify_group_unlock(group);
        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, __u32 umask)
{
        return fanotify_remove_mark(group, &real_mount(mnt)->mnt_fsnotify_marks,
                                    mask, flags, umask);
}

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

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

static bool fanotify_mark_update_flags(struct fsnotify_mark *fsn_mark,
                                       unsigned int fan_flags)
{
        bool want_iref = !(fan_flags & FAN_MARK_EVICTABLE);
        bool recalc = false;

        /*
         * Setting FAN_MARK_IGNORED_SURV_MODIFY for the first time may lead to
         * the removal of the FS_MODIFY bit in calculated mask if it was set
         * because of an ignored mask that is now going to survive FS_MODIFY.
         */
        if ((fan_flags & FAN_MARK_IGNORED_MASK) &&
            (fan_flags & FAN_MARK_IGNORED_SURV_MODIFY) &&
            !(fsn_mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY)) {
                fsn_mark->flags |= FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY;
                if (!(fsn_mark->mask & FS_MODIFY))
                        recalc = true;
        }

        if (fsn_mark->connector->type != FSNOTIFY_OBJ_TYPE_INODE ||
            want_iref == !(fsn_mark->flags & FSNOTIFY_MARK_FLAG_NO_IREF))
                return recalc;

        /*
         * NO_IREF may be removed from a mark, but not added.
         * When removed, fsnotify_recalc_mask() will take the inode ref.
         */
        WARN_ON_ONCE(!want_iref);
        fsn_mark->flags &= ~FSNOTIFY_MARK_FLAG_NO_IREF;

        return true;
}

static bool fanotify_mark_add_to_mask(struct fsnotify_mark *fsn_mark,
                                      __u32 mask, unsigned int fan_flags)
{
        bool recalc;

        spin_lock(&fsn_mark->lock);
        if (!(fan_flags & FAN_MARK_IGNORED_MASK))
                fsn_mark->mask |= mask;
        else
                fsn_mark->ignored_mask |= mask;

        recalc = fsnotify_calc_mask(fsn_mark) &
                ~fsnotify_conn_mask(fsn_mark->connector);

        recalc |= fanotify_mark_update_flags(fsn_mark, fan_flags);
        spin_unlock(&fsn_mark->lock);

        return recalc;
}

static struct fsnotify_mark *fanotify_add_new_mark(struct fsnotify_group *group,
                                                   fsnotify_connp_t *connp,
                                                   unsigned int obj_type,
                                                   unsigned int fan_flags,
                                                   __kernel_fsid_t *fsid)
{
        struct ucounts *ucounts = group->fanotify_data.ucounts;
        struct fsnotify_mark *mark;
        int ret;

        /*
         * Enforce per user marks limits per user in all containing user ns.
         * A group with FAN_UNLIMITED_MARKS does not contribute to mark count
         * in the limited groups account.
         */
        if (!FAN_GROUP_FLAG(group, FAN_UNLIMITED_MARKS) &&
            !inc_ucount(ucounts->ns, ucounts->uid, UCOUNT_FANOTIFY_MARKS))
                return ERR_PTR(-ENOSPC);

        mark = kmem_cache_alloc(fanotify_mark_cache, GFP_KERNEL);
        if (!mark) {
                ret = -ENOMEM;
                goto out_dec_ucounts;
        }

        fsnotify_init_mark(mark, group);
        if (fan_flags & FAN_MARK_EVICTABLE)
                mark->flags |= FSNOTIFY_MARK_FLAG_NO_IREF;

        ret = fsnotify_add_mark_locked(mark, connp, obj_type, 0, fsid);
        if (ret) {
                fsnotify_put_mark(mark);
                goto out_dec_ucounts;
        }

        return mark;

out_dec_ucounts:
        if (!FAN_GROUP_FLAG(group, FAN_UNLIMITED_MARKS))
                dec_ucount(ucounts, UCOUNT_FANOTIFY_MARKS);
        return ERR_PTR(ret);
}

static int fanotify_group_init_error_pool(struct fsnotify_group *group)
{
        if (mempool_initialized(&group->fanotify_data.error_events_pool))
                return 0;

        return mempool_init_kmalloc_pool(&group->fanotify_data.error_events_pool,
                                         FANOTIFY_DEFAULT_FEE_POOL_SIZE,
                                         sizeof(struct fanotify_error_event));
}

static int fanotify_add_mark(struct fsnotify_group *group,
                             fsnotify_connp_t *connp, unsigned int obj_type,
                             __u32 mask, unsigned int fan_flags,
                             __kernel_fsid_t *fsid)
{
        struct fsnotify_mark *fsn_mark;
        bool recalc;
        int ret = 0;

        fsnotify_group_lock(group);
        fsn_mark = fsnotify_find_mark(connp, group);
        if (!fsn_mark) {
                fsn_mark = fanotify_add_new_mark(group, connp, obj_type,
                                                 fan_flags, fsid);
                if (IS_ERR(fsn_mark)) {
                        fsnotify_group_unlock(group);
                        return PTR_ERR(fsn_mark);
                }
        }

        /*
         * Non evictable mark cannot be downgraded to evictable mark.
         */
        if (fan_flags & FAN_MARK_EVICTABLE &&
            !(fsn_mark->flags & FSNOTIFY_MARK_FLAG_NO_IREF)) {
                ret = -EEXIST;
                goto out;
        }

        /*
         * Error events are pre-allocated per group, only if strictly
         * needed (i.e. FAN_FS_ERROR was requested).
         */
        if (!(fan_flags & FAN_MARK_IGNORED_MASK) && (mask & FAN_FS_ERROR)) {
                ret = fanotify_group_init_error_pool(group);
                if (ret)
                        goto out;
        }

        recalc = fanotify_mark_add_to_mask(fsn_mark, mask, fan_flags);
        if (recalc)
                fsnotify_recalc_mask(fsn_mark->connector);

out:
        fsnotify_group_unlock(group);

        fsnotify_put_mark(fsn_mark);
        return ret;
}

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);
}

static struct fsnotify_event *fanotify_alloc_overflow_event(void)
{
        struct fanotify_event *oevent;

        oevent = kmalloc(sizeof(*oevent), GFP_KERNEL_ACCOUNT);
        if (!oevent)
                return NULL;

        fanotify_init_event(oevent, 0, FS_Q_OVERFLOW);
        oevent->type = FANOTIFY_EVENT_TYPE_OVERFLOW;

        return &oevent->fse;
}

static struct hlist_head *fanotify_alloc_merge_hash(void)
{
        struct hlist_head *hash;

        hash = kmalloc(sizeof(struct hlist_head) << FANOTIFY_HTABLE_BITS,
                       GFP_KERNEL_ACCOUNT);
        if (!hash)
                return NULL;

        __hash_init(hash, FANOTIFY_HTABLE_SIZE);

        return hash;
}

/* fanotify syscalls */
SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
{
        struct fsnotify_group *group;
        int f_flags, fd;
        unsigned int fid_mode = flags & FANOTIFY_FID_BITS;
        unsigned int class = flags & FANOTIFY_CLASS_BITS;
        unsigned int internal_flags = 0;

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

        if (!capable(CAP_SYS_ADMIN)) {
                /*
                 * An unprivileged user can setup an fanotify group with
                 * limited functionality - an unprivileged group is limited to
                 * notification events with file handles and it cannot use
                 * unlimited queue/marks.
                 */
                if ((flags & FANOTIFY_ADMIN_INIT_FLAGS) || !fid_mode)
                        return -EPERM;

                /*
                 * Setting the internal flag FANOTIFY_UNPRIV on the group
                 * prevents setting mount/filesystem marks on this group and
                 * prevents reporting pid and open fd in events.
                 */
                internal_flags |= FANOTIFY_UNPRIV;
        }

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

        /*
         * A pidfd can only be returned for a thread-group leader; thus
         * FAN_REPORT_PIDFD and FAN_REPORT_TID need to remain mutually
         * exclusive.
         */
        if ((flags & FAN_REPORT_PIDFD) && (flags & FAN_REPORT_TID))
                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 (fid_mode && class != FAN_CLASS_NOTIF)
                return -EINVAL;

        /*
         * Child name is reported with parent fid so requires dir fid.
         * We can report both child fid and dir fid with or without name.
         */
        if ((fid_mode & FAN_REPORT_NAME) && !(fid_mode & FAN_REPORT_DIR_FID))
                return -EINVAL;

        /*
         * FAN_REPORT_TARGET_FID requires FAN_REPORT_NAME and FAN_REPORT_FID
         * and is used as an indication to report both dir and child fid on all
         * dirent events.
         */
        if ((fid_mode & FAN_REPORT_TARGET_FID) &&
            (!(fid_mode & FAN_REPORT_NAME) || !(fid_mode & FAN_REPORT_FID)))
                return -EINVAL;

        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,
                                     FSNOTIFY_GROUP_USER | FSNOTIFY_GROUP_NOFS);
        if (IS_ERR(group)) {
                return PTR_ERR(group);
        }

        /* Enforce groups limits per user in all containing user ns */
        group->fanotify_data.ucounts = inc_ucount(current_user_ns(),
                                                  current_euid(),
                                                  UCOUNT_FANOTIFY_GROUPS);
        if (!group->fanotify_data.ucounts) {
                fd = -EMFILE;
                goto out_destroy_group;
        }

        group->fanotify_data.flags = flags | internal_flags;
        group->memcg = get_mem_cgroup_from_mm(current->mm);

        group->fanotify_data.merge_hash = fanotify_alloc_merge_hash();
        if (!group->fanotify_data.merge_hash) {
                fd = -ENOMEM;
                goto out_destroy_group;
        }

        group->overflow_event = fanotify_alloc_overflow_event();
        if (unlikely(!group->overflow_event)) {
                fd = -ENOMEM;
                goto out_destroy_group;
        }

        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 (class) {
        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_max_queued_events;
        }

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

        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;
}

static int fanotify_test_fsid(struct dentry *dentry, __kernel_fsid_t *fsid)
{
        __kernel_fsid_t root_fsid;
        int err;

        /*
         * Make sure dentry is not of a filesystem with zero fsid (e.g. fuse).
         */
        err = vfs_get_fsid(dentry, fsid);
        if (err)
                return err;

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

        /*
         * Make sure dentry is not of a filesystem subvolume (e.g. btrfs)
         * which uses a different fsid than sb root.
         */
        err = vfs_get_fsid(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;

        return 0;
}

/* Check if filesystem can encode a unique fid */
static int fanotify_test_fid(struct dentry *dentry)
{
        /*
         * 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 (!dentry->d_sb->s_export_op ||
            !dentry->d_sb->s_export_op->fh_to_dentry)
                return -EOPNOTSUPP;

        return 0;
}

static int fanotify_events_supported(struct fsnotify_group *group,
                                     struct path *path, __u64 mask,
                                     unsigned int flags)
{
        unsigned int mark_type = flags & FANOTIFY_MARK_TYPE_BITS;
        /* Strict validation of events in non-dir inode mask with v5.17+ APIs */
        bool strict_dir_events = FAN_GROUP_FLAG(group, FAN_REPORT_TARGET_FID) ||
                                 (mask & FAN_RENAME);

        /*
         * 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;

        /*
         * We shouldn't have allowed setting dirent events and the directory
         * flags FAN_ONDIR and FAN_EVENT_ON_CHILD in mask of non-dir inode,
         * but because we always allowed it, error only when using new APIs.
         */
        if (strict_dir_events && mark_type == FAN_MARK_INODE &&
            !d_is_dir(path->dentry) && (mask & FANOTIFY_DIRONLY_EVENT_BITS))
                return -ENOTDIR;

        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;
        bool ignored = flags & FAN_MARK_IGNORED_MASK;
        unsigned int obj_type, fid_mode;
        u32 umask = 0;
        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 (upper_32_bits(mask))
                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:
        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;

        /* Event flags (ONDIR, ON_CHILD) are meaningless in ignored mask */
        if (ignored)
                mask &= ~FANOTIFY_EVENT_FLAGS;

        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;

        /*
         * An unprivileged user is not allowed to setup mount nor filesystem
         * marks.  This also includes setting up such marks by a group that
         * was initialized by an unprivileged user.
         */
        ret = -EPERM;
        if ((!capable(CAP_SYS_ADMIN) ||
             FAN_GROUP_FLAG(group, FANOTIFY_UNPRIV)) &&
            mark_type != FAN_MARK_INODE)
                goto fput_and_out;

        /*
         * 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;

        if (mask & FAN_FS_ERROR &&
            mark_type != FAN_MARK_FILESYSTEM)
                goto fput_and_out;

        /*
         * Evictable is only relevant for inode marks, because only inode object
         * can be evicted on memory pressure.
         */
        if (flags & FAN_MARK_EVICTABLE &&
             mark_type != FAN_MARK_INODE)
                goto fput_and_out;

        /*
         * Events that do not carry enough information to report
         * event->fd require a group that supports reporting fid.  Those
         * events are not supported on a mount mark, because they do not
         * carry enough information (i.e. path) to be filtered by mount
         * point.
         */
        fid_mode = FAN_GROUP_FLAG(group, FANOTIFY_FID_BITS);
        if (mask & ~(FANOTIFY_FD_EVENTS|FANOTIFY_EVENT_FLAGS) &&
            (!fid_mode || mark_type == FAN_MARK_MOUNT))
                goto fput_and_out;

        /*
         * FAN_RENAME uses special info type records to report the old and
         * new parent+name.  Reporting only old and new parent id is less
         * useful and was not implemented.
         */
        if (mask & FAN_RENAME && !(fid_mode & FAN_REPORT_NAME))
                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(group, &path, mask, flags);
                if (ret)
                        goto path_put_and_out;
        }

        if (fid_mode) {
                ret = fanotify_test_fsid(path.dentry, &__fsid);
                if (ret)
                        goto path_put_and_out;

                ret = fanotify_test_fid(path.dentry);
                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;

        /* Mask out FAN_EVENT_ON_CHILD flag for sb/mount/non-dir marks */
        if (mnt || !S_ISDIR(inode->i_mode)) {
                mask &= ~FAN_EVENT_ON_CHILD;
                umask = FAN_EVENT_ON_CHILD;
                /*
                 * If group needs to report parent fid, register for getting
                 * events with parent/name info for non-directory.
                 */
                if ((fid_mode & FAN_REPORT_DIR_FID) &&
                    (flags & FAN_MARK_ADD) && !ignored)
                        mask |= FAN_EVENT_ON_CHILD;
        }

        /* 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, umask);
                else if (mark_type == FAN_MARK_FILESYSTEM)
                        ret = fanotify_remove_sb_mark(group, mnt->mnt_sb, mask,
                                                      flags, umask);
                else
                        ret = fanotify_remove_inode_mark(group, inode, mask,
                                                         flags, umask);
                break;
        default:
                ret = -EINVAL;
        }

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

#ifndef CONFIG_ARCH_SPLIT_ARG64
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);
}
#endif

#if defined(CONFIG_ARCH_SPLIT_ARG64) || defined(CONFIG_COMPAT)
SYSCALL32_DEFINE6(fanotify_mark,
                                int, fanotify_fd, unsigned int, flags,
                                SC_ARG64(mask), int, dfd,
                                const char  __user *, pathname)
{
        return do_fanotify_mark(fanotify_fd, flags, SC_VAL64(__u64, mask),
                                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)
{
        struct sysinfo si;
        int max_marks;

        si_meminfo(&si);
        /*
         * Allow up to 1% of addressable memory to be accounted for per user
         * marks limited to the range [8192, 1048576]. mount and sb marks are
         * a lot cheaper than inode marks, but there is no reason for a user
         * to have many of those, so calculate by the cost of inode marks.
         */
        max_marks = (((si.totalram - si.totalhigh) / 100) << PAGE_SHIFT) /
                    INODE_MARK_COST;
        max_marks = clamp(max_marks, FANOTIFY_OLD_DEFAULT_MAX_MARKS,
                                     FANOTIFY_DEFAULT_MAX_USER_MARKS);

        BUILD_BUG_ON(FANOTIFY_INIT_FLAGS & FANOTIFY_INTERNAL_GROUP_FLAGS);
        BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 12);
        BUILD_BUG_ON(HWEIGHT32(FANOTIFY_MARK_FLAGS) != 10);

        fanotify_mark_cache = KMEM_CACHE(fsnotify_mark,
                                         SLAB_PANIC|SLAB_ACCOUNT);
        fanotify_fid_event_cachep = KMEM_CACHE(fanotify_fid_event,
                                               SLAB_PANIC);
        fanotify_path_event_cachep = KMEM_CACHE(fanotify_path_event,
                                                SLAB_PANIC);
        if (IS_ENABLED(CONFIG_FANOTIFY_ACCESS_PERMISSIONS)) {
                fanotify_perm_event_cachep =
                        KMEM_CACHE(fanotify_perm_event, SLAB_PANIC);
        }

        fanotify_max_queued_events = FANOTIFY_DEFAULT_MAX_EVENTS;
        init_user_ns.ucount_max[UCOUNT_FANOTIFY_GROUPS] =
                                        FANOTIFY_DEFAULT_MAX_GROUPS;
        init_user_ns.ucount_max[UCOUNT_FANOTIFY_MARKS] = max_marks;
        fanotify_sysctls_init();

        return 0;
}
device_initcall(fanotify_user_setup);