// SPDX-License-Identifier: GPL-2.0
#include <linux/fanotify.h>
#include <linux/fsnotify_backend.h>
#include <linux/init.h>
#include <linux/jiffies.h>
#include <linux/kernel.h> /* UINT_MAX */
#include <linux/mount.h>
#include <linux/sched.h>
#include <linux/sched/user.h>
#include <linux/sched/signal.h>
#include <linux/types.h>
#include <linux/wait.h>
#include <linux/audit.h>
#include <linux/sched/mm.h>
#include <linux/statfs.h>
#include <linux/stringhash.h>

#include "fanotify.h"

static bool fanotify_path_equal(const struct path *p1, const struct path *p2)
{
        return p1->mnt == p2->mnt && p1->dentry == p2->dentry;
}

static unsigned int fanotify_hash_path(const struct path *path)
{
        return hash_ptr(path->dentry, FANOTIFY_EVENT_HASH_BITS) ^
                hash_ptr(path->mnt, FANOTIFY_EVENT_HASH_BITS);
}

static unsigned int fanotify_hash_fsid(__kernel_fsid_t *fsid)
{
        return hash_32(fsid->val[0], FANOTIFY_EVENT_HASH_BITS) ^
                hash_32(fsid->val[1], FANOTIFY_EVENT_HASH_BITS);
}

static bool fanotify_fh_equal(struct fanotify_fh *fh1,
                              struct fanotify_fh *fh2)
{
        if (fh1->type != fh2->type || fh1->len != fh2->len)
                return false;

        return !fh1->len ||
                !memcmp(fanotify_fh_buf(fh1), fanotify_fh_buf(fh2), fh1->len);
}

static unsigned int fanotify_hash_fh(struct fanotify_fh *fh)
{
        long salt = (long)fh->type | (long)fh->len << 8;

        /*
         * full_name_hash() works long by long, so it handles fh buf optimally.
         */
        return full_name_hash((void *)salt, fanotify_fh_buf(fh), fh->len);
}

static bool fanotify_fid_event_equal(struct fanotify_fid_event *ffe1,
                                     struct fanotify_fid_event *ffe2)
{
        /* Do not merge fid events without object fh */
        if (!ffe1->object_fh.len)
                return false;

        return fanotify_fsid_equal(&ffe1->fsid, &ffe2->fsid) &&
                fanotify_fh_equal(&ffe1->object_fh, &ffe2->object_fh);
}

static bool fanotify_info_equal(struct fanotify_info *info1,
                                struct fanotify_info *info2)
{
        if (info1->dir_fh_totlen != info2->dir_fh_totlen ||
            info1->dir2_fh_totlen != info2->dir2_fh_totlen ||
            info1->file_fh_totlen != info2->file_fh_totlen ||
            info1->name_len != info2->name_len ||
            info1->name2_len != info2->name2_len)
                return false;

        if (info1->dir_fh_totlen &&
            !fanotify_fh_equal(fanotify_info_dir_fh(info1),
                               fanotify_info_dir_fh(info2)))
                return false;

        if (info1->dir2_fh_totlen &&
            !fanotify_fh_equal(fanotify_info_dir2_fh(info1),
                               fanotify_info_dir2_fh(info2)))
                return false;

        if (info1->file_fh_totlen &&
            !fanotify_fh_equal(fanotify_info_file_fh(info1),
                               fanotify_info_file_fh(info2)))
                return false;

        if (info1->name_len &&
            memcmp(fanotify_info_name(info1), fanotify_info_name(info2),
                   info1->name_len))
                return false;

        return !info1->name2_len ||
                !memcmp(fanotify_info_name2(info1), fanotify_info_name2(info2),
                        info1->name2_len);
}

static bool fanotify_name_event_equal(struct fanotify_name_event *fne1,
                                      struct fanotify_name_event *fne2)
{
        struct fanotify_info *info1 = &fne1->info;
        struct fanotify_info *info2 = &fne2->info;

        /* Do not merge name events without dir fh */
        if (!info1->dir_fh_totlen)
                return false;

        if (!fanotify_fsid_equal(&fne1->fsid, &fne2->fsid))
                return false;

        return fanotify_info_equal(info1, info2);
}

static bool fanotify_error_event_equal(struct fanotify_error_event *fee1,
                                       struct fanotify_error_event *fee2)
{
        /* Error events against the same file system are always merged. */
        if (!fanotify_fsid_equal(&fee1->fsid, &fee2->fsid))
                return false;

        return true;
}

static bool fanotify_should_merge(struct fanotify_event *old,
                                  struct fanotify_event *new)
{
        pr_debug("%s: old=%p new=%p\n", __func__, old, new);

        if (old->hash != new->hash ||
            old->type != new->type || old->pid != new->pid)
                return false;

        /*
         * We want to merge many dirent events in the same dir (i.e.
         * creates/unlinks/renames), but we do not want to merge dirent
         * events referring to subdirs with dirent events referring to
         * non subdirs, otherwise, user won't be able to tell from a
         * mask FAN_CREATE|FAN_DELETE|FAN_ONDIR if it describes mkdir+
         * unlink pair or rmdir+create pair of events.
         */
        if ((old->mask & FS_ISDIR) != (new->mask & FS_ISDIR))
                return false;

        /*
         * FAN_RENAME event is reported with special info record types,
         * so we cannot merge it with other events.
         */
        if ((old->mask & FAN_RENAME) != (new->mask & FAN_RENAME))
                return false;

        switch (old->type) {
        case FANOTIFY_EVENT_TYPE_PATH:
                return fanotify_path_equal(fanotify_event_path(old),
                                           fanotify_event_path(new));
        case FANOTIFY_EVENT_TYPE_FID:
                return fanotify_fid_event_equal(FANOTIFY_FE(old),
                                                FANOTIFY_FE(new));
        case FANOTIFY_EVENT_TYPE_FID_NAME:
                return fanotify_name_event_equal(FANOTIFY_NE(old),
                                                 FANOTIFY_NE(new));
        case FANOTIFY_EVENT_TYPE_FS_ERROR:
                return fanotify_error_event_equal(FANOTIFY_EE(old),
                                                  FANOTIFY_EE(new));
        case FANOTIFY_EVENT_TYPE_MNT:
                return false;
        default:
                WARN_ON_ONCE(1);
        }

        return false;
}

/* Limit event merges to limit CPU overhead per event */
#define FANOTIFY_MAX_MERGE_EVENTS 128

/* and the list better be locked by something too! */
static int fanotify_merge(struct fsnotify_group *group,
                          struct fsnotify_event *event)
{
        struct fanotify_event *old, *new = FANOTIFY_E(event);
        unsigned int bucket = fanotify_event_hash_bucket(group, new);
        struct hlist_head *hlist = &group->fanotify_data.merge_hash[bucket];
        int i = 0;

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

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

        hlist_for_each_entry(old, hlist, merge_list) {
                if (++i > FANOTIFY_MAX_MERGE_EVENTS)
                        break;
                if (fanotify_should_merge(old, new)) {
                        old->mask |= new->mask;

                        if (fanotify_is_error_event(old->mask))
                                FANOTIFY_EE(old)->err_count++;

                        return 1;
                }
        }

        return 0;
}

/*
 * Wait for response to permission event. The function also takes care of
 * freeing the permission event (or offloads that in case the wait is canceled
 * by a signal). The function returns 0 in case access got allowed by userspace,
 * -EPERM in case userspace disallowed the access, and -ERESTARTSYS in case
 * the wait got interrupted by a signal.
 */
static int fanotify_get_response(struct fsnotify_group *group,
                                 struct fanotify_perm_event *event,
                                 struct fsnotify_iter_info *iter_info)
{
        int ret, errno;

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

        ret = wait_event_state(group->fanotify_data.access_waitq,
                                  event->state == FAN_EVENT_ANSWERED,
                                  (TASK_KILLABLE|TASK_FREEZABLE));

        /* Signal pending? */
        if (ret < 0) {
                spin_lock(&group->notification_lock);
                /* Event reported to userspace and no answer yet? */
                if (event->state == FAN_EVENT_REPORTED) {
                        /* Event will get freed once userspace answers to it */
                        event->state = FAN_EVENT_CANCELED;
                        spin_unlock(&group->notification_lock);
                        return ret;
                }
                /* Event not yet reported? Just remove it. */
                if (event->state == FAN_EVENT_INIT) {
                        fsnotify_remove_queued_event(group, &event->fae.fse);
                        /* Permission events are not supposed to be hashed */
                        WARN_ON_ONCE(!hlist_unhashed(&event->fae.merge_list));
                }
                /*
                 * Event may be also answered in case signal delivery raced
                 * with wakeup. In that case we have nothing to do besides
                 * freeing the event and reporting error.
                 */
                spin_unlock(&group->notification_lock);
                goto out;
        }

        /* userspace responded, convert to something usable */
        switch (event->response & FANOTIFY_RESPONSE_ACCESS) {
        case FAN_ALLOW:
                ret = 0;
                break;
        case FAN_DENY:
                /* Check custom errno from pre-content events */
                errno = fanotify_get_response_errno(event->response);
                if (errno) {
                        ret = -errno;
                        break;
                }
                fallthrough;
        default:
                ret = -EPERM;
        }

        /* Check if the response should be audited */
        if (event->response & FAN_AUDIT) {
                u32 response = event->response &
                        (FANOTIFY_RESPONSE_ACCESS | FANOTIFY_RESPONSE_FLAGS);
                audit_fanotify(response & ~FAN_AUDIT, &event->audit_rule);
        }

        pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
                 group, event, ret);
out:
        fsnotify_destroy_event(group, &event->fae.fse);

        return ret;
}

/*
 * This function returns a mask for an event that only contains the flags
 * that have been specifically requested by the user. Flags that may have
 * been included within the event mask, but have not been explicitly
 * requested by the user, will not be present in the returned mask.
 */
static u32 fanotify_group_event_mask(struct fsnotify_group *group,
                                     struct fsnotify_iter_info *iter_info,
                                     u32 *match_mask, u32 event_mask,
                                     const void *data, int data_type,
                                     struct inode *dir)
{
        __u32 marks_mask = 0, marks_ignore_mask = 0;
        __u32 test_mask, user_mask = FANOTIFY_OUTGOING_EVENTS |
                                     FANOTIFY_EVENT_FLAGS;
        const struct path *path = fsnotify_data_path(data, data_type);
        unsigned int fid_mode = FAN_GROUP_FLAG(group, FANOTIFY_FID_BITS);
        struct fsnotify_mark *mark;
        bool ondir = event_mask & FAN_ONDIR;
        int type;

        pr_debug("%s: report_mask=%x mask=%x data=%p data_type=%d\n",
                 __func__, iter_info->report_mask, event_mask, data, data_type);

        if (FAN_GROUP_FLAG(group, FAN_REPORT_MNT)) {
                if (data_type != FSNOTIFY_EVENT_MNT)
                        return 0;
        } else if (!fid_mode) {
                /* Do we have path to open a file descriptor? */
                if (!path)
                        return 0;
                /* Path type events are only relevant for files and dirs */
                if (!d_is_reg(path->dentry) && !d_can_lookup(path->dentry))
                        return 0;
        } else if (!(fid_mode & FAN_REPORT_FID)) {
                /* Do we have a directory inode to report? */
                if (!dir && !ondir)
                        return 0;
        }

        fsnotify_foreach_iter_mark_type(iter_info, mark, type) {
                /*
                 * Apply ignore mask depending on event flags in ignore mask.
                 */
                marks_ignore_mask |=
                        fsnotify_effective_ignore_mask(mark, ondir, type);

                /*
                 * Send the event depending on event flags in mark mask.
                 */
                if (!fsnotify_mask_applicable(mark->mask, ondir, type))
                        continue;

                marks_mask |= mark->mask;

                /* Record the mark types of this group that matched the event */
                *match_mask |= 1U << type;
        }

        test_mask = event_mask & marks_mask & ~marks_ignore_mask;

        /*
         * For dirent modification events (create/delete/move) that do not carry
         * the child entry name information, we report FAN_ONDIR for mkdir/rmdir
         * so user can differentiate them from creat/unlink.
         *
         * For backward compatibility and consistency, do not report FAN_ONDIR
         * to user in legacy fanotify mode (reporting fd) and report FAN_ONDIR
         * to user in fid mode for all event types.
         *
         * We never report FAN_EVENT_ON_CHILD to user, but we do pass it in to
         * fanotify_alloc_event() when group is reporting fid as indication
         * that event happened on child.
         */
        if (fid_mode) {
                /* Do not report event flags without any event */
                if (!(test_mask & ~FANOTIFY_EVENT_FLAGS))
                        return 0;
        } else {
                user_mask &= ~FANOTIFY_EVENT_FLAGS;
        }

        return test_mask & user_mask;
}

/*
 * Check size needed to encode fanotify_fh.
 *
 * Return size of encoded fh without fanotify_fh header.
 * Return 0 on failure to encode.
 */
static int fanotify_encode_fh_len(struct inode *inode)
{
        int dwords = 0;
        int fh_len;

        if (!inode)
                return 0;

        exportfs_encode_fid(inode, NULL, &dwords);
        fh_len = dwords << 2;

        /*
         * struct fanotify_error_event might be preallocated and is
         * limited to MAX_HANDLE_SZ.  This should never happen, but
         * safeguard by forcing an invalid file handle.
         */
        if (WARN_ON_ONCE(fh_len > MAX_HANDLE_SZ))
                return 0;

        return fh_len;
}

/*
 * Encode fanotify_fh.
 *
 * Return total size of encoded fh including fanotify_fh header.
 * Return 0 on failure to encode.
 */
static int fanotify_encode_fh(struct fanotify_fh *fh, struct inode *inode,
                              unsigned int fh_len, unsigned int *hash,
                              gfp_t gfp)
{
        int dwords, type = 0;
        char *ext_buf = NULL;
        void *buf = fh + 1;
        int err;

        fh->type = FILEID_ROOT;
        fh->len = 0;
        fh->flags = 0;

        /*
         * Invalid FHs are used by FAN_FS_ERROR for errors not
         * linked to any inode. The f_handle won't be reported
         * back to userspace.
         */
        if (!inode)
                goto out;

        /*
         * !gpf means preallocated variable size fh, but fh_len could
         * be zero in that case if encoding fh len failed.
         */
        err = -ENOENT;
        if (fh_len < 4 || WARN_ON_ONCE(fh_len % 4) || fh_len > MAX_HANDLE_SZ)
                goto out_err;

        /* No external buffer in a variable size allocated fh */
        if (gfp && fh_len > FANOTIFY_INLINE_FH_LEN) {
                /* Treat failure to allocate fh as failure to encode fh */
                err = -ENOMEM;
                ext_buf = kmalloc(fh_len, gfp);
                if (!ext_buf)
                        goto out_err;

                *fanotify_fh_ext_buf_ptr(fh) = ext_buf;
                buf = ext_buf;
                fh->flags |= FANOTIFY_FH_FLAG_EXT_BUF;
        }

        dwords = fh_len >> 2;
        type = exportfs_encode_fid(inode, buf, &dwords);
        err = -EINVAL;
        /*
         * Unlike file_handle, type and len of struct fanotify_fh are u8.
         * Traditionally, filesystem return handle_type < 0xff, but there
         * is no enforecement for that in vfs.
         */
        BUILD_BUG_ON(MAX_HANDLE_SZ > 0xff || FILEID_INVALID > 0xff);
        if (type <= 0 || type >= FILEID_INVALID || fh_len != dwords << 2)
                goto out_err;

        fh->type = type;
        fh->len = fh_len;

out:
        /*
         * Mix fh into event merge key.  Hash might be NULL in case of
         * unhashed FID events (i.e. FAN_FS_ERROR).
         */
        if (hash)
                *hash ^= fanotify_hash_fh(fh);

        return FANOTIFY_FH_HDR_LEN + fh_len;

out_err:
        pr_warn_ratelimited("fanotify: failed to encode fid (type=%d, len=%d, err=%i)\n",
                            type, fh_len, err);
        kfree(ext_buf);
        *fanotify_fh_ext_buf_ptr(fh) = NULL;
        /* Report the event without a file identifier on encode error */
        fh->type = FILEID_INVALID;
        fh->len = 0;
        return 0;
}

/*
 * FAN_REPORT_FID is ambiguous in that it reports the fid of the child for
 * some events and the fid of the parent for create/delete/move events.
 *
 * With the FAN_REPORT_TARGET_FID flag, the fid of the child is reported
 * also in create/delete/move events in addition to the fid of the parent
 * and the name of the child.
 */
static inline bool fanotify_report_child_fid(unsigned int fid_mode, u32 mask)
{
        if (mask & ALL_FSNOTIFY_DIRENT_EVENTS)
                return (fid_mode & FAN_REPORT_TARGET_FID);

        return (fid_mode & FAN_REPORT_FID) && !(mask & FAN_ONDIR);
}

/*
 * The inode to use as identifier when reporting fid depends on the event
 * and the group flags.
 *
 * With the group flag FAN_REPORT_TARGET_FID, always report the child fid.
 *
 * Without the group flag FAN_REPORT_TARGET_FID, report the modified directory
 * fid on dirent events and the child fid otherwise.
 *
 * For example:
 * FS_ATTRIB reports the child fid even if reported on a watched parent.
 * FS_CREATE reports the modified dir fid without FAN_REPORT_TARGET_FID.
 *       and reports the created child fid with FAN_REPORT_TARGET_FID.
 */
static struct inode *fanotify_fid_inode(u32 event_mask, const void *data,
                                        int data_type, struct inode *dir,
                                        unsigned int fid_mode)
{
        if ((event_mask & ALL_FSNOTIFY_DIRENT_EVENTS) &&
            !(fid_mode & FAN_REPORT_TARGET_FID))
                return dir;

        return fsnotify_data_inode(data, data_type);
}

/*
 * The inode to use as identifier when reporting dir fid depends on the event.
 * Report the modified directory inode on dirent modification events.
 * Report the "victim" inode if "victim" is a directory.
 * Report the parent inode if "victim" is not a directory and event is
 * reported to parent.
 * Otherwise, do not report dir fid.
 */
static struct inode *fanotify_dfid_inode(u32 event_mask, const void *data,
                                         int data_type, struct inode *dir)
{
        struct inode *inode = fsnotify_data_inode(data, data_type);

        if (event_mask & ALL_FSNOTIFY_DIRENT_EVENTS)
                return dir;

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

        return dir;
}

static struct fanotify_event *fanotify_alloc_path_event(const struct path *path,
                                                        unsigned int *hash,
                                                        gfp_t gfp)
{
        struct fanotify_path_event *pevent;

        pevent = kmem_cache_alloc(fanotify_path_event_cachep, gfp);
        if (!pevent)
                return NULL;

        pevent->fae.type = FANOTIFY_EVENT_TYPE_PATH;
        pevent->path = *path;
        *hash ^= fanotify_hash_path(path);
        path_get(path);

        return &pevent->fae;
}

static struct fanotify_event *fanotify_alloc_mnt_event(u64 mnt_id, gfp_t gfp)
{
        struct fanotify_mnt_event *pevent;

        pevent = kmem_cache_alloc(fanotify_mnt_event_cachep, gfp);
        if (!pevent)
                return NULL;

        pevent->fae.type = FANOTIFY_EVENT_TYPE_MNT;
        pevent->mnt_id = mnt_id;

        return &pevent->fae;
}

static struct fanotify_event *fanotify_alloc_perm_event(const void *data,
                                                        int data_type,
                                                        gfp_t gfp)
{
        const struct path *path = fsnotify_data_path(data, data_type);
        const struct file_range *range =
                            fsnotify_data_file_range(data, data_type);
        struct fanotify_perm_event *pevent;

        pevent = kmem_cache_alloc(fanotify_perm_event_cachep, gfp);
        if (!pevent)
                return NULL;

        pevent->fae.type = FANOTIFY_EVENT_TYPE_PATH_PERM;
        pevent->response = 0;
        pevent->hdr.type = FAN_RESPONSE_INFO_NONE;
        pevent->hdr.pad = 0;
        pevent->hdr.len = 0;
        pevent->state = FAN_EVENT_INIT;
        pevent->path = *path;
        /* NULL ppos means no range info */
        pevent->ppos = range ? &range->pos : NULL;
        pevent->count = range ? range->count : 0;
        path_get(path);

        return &pevent->fae;
}

static struct fanotify_event *fanotify_alloc_fid_event(struct inode *id,
                                                       __kernel_fsid_t *fsid,
                                                       unsigned int *hash,
                                                       gfp_t gfp)
{
        struct fanotify_fid_event *ffe;

        ffe = kmem_cache_alloc(fanotify_fid_event_cachep, gfp);
        if (!ffe)
                return NULL;

        ffe->fae.type = FANOTIFY_EVENT_TYPE_FID;
        ffe->fsid = *fsid;
        *hash ^= fanotify_hash_fsid(fsid);
        fanotify_encode_fh(&ffe->object_fh, id, fanotify_encode_fh_len(id),
                           hash, gfp);

        return &ffe->fae;
}

static struct fanotify_event *fanotify_alloc_name_event(struct inode *dir,
                                                        __kernel_fsid_t *fsid,
                                                        const struct qstr *name,
                                                        struct inode *child,
                                                        struct dentry *moved,
                                                        unsigned int *hash,
                                                        gfp_t gfp)
{
        struct fanotify_name_event *fne;
        struct fanotify_info *info;
        struct fanotify_fh *dfh, *ffh;
        struct inode *dir2 = moved ? d_inode(moved->d_parent) : NULL;
        const struct qstr *name2 = moved ? &moved->d_name : NULL;
        unsigned int dir_fh_len = fanotify_encode_fh_len(dir);
        unsigned int dir2_fh_len = fanotify_encode_fh_len(dir2);
        unsigned int child_fh_len = fanotify_encode_fh_len(child);
        unsigned long name_len = name ? name->len : 0;
        unsigned long name2_len = name2 ? name2->len : 0;
        unsigned int len, size;

        /* Reserve terminating null byte even for empty name */
        size = sizeof(*fne) + name_len + name2_len + 2;
        if (dir_fh_len)
                size += FANOTIFY_FH_HDR_LEN + dir_fh_len;
        if (dir2_fh_len)
                size += FANOTIFY_FH_HDR_LEN + dir2_fh_len;
        if (child_fh_len)
                size += FANOTIFY_FH_HDR_LEN + child_fh_len;
        fne = kmalloc(size, gfp);
        if (!fne)
                return NULL;

        fne->fae.type = FANOTIFY_EVENT_TYPE_FID_NAME;
        fne->fsid = *fsid;
        *hash ^= fanotify_hash_fsid(fsid);
        info = &fne->info;
        fanotify_info_init(info);
        if (dir_fh_len) {
                dfh = fanotify_info_dir_fh(info);
                len = fanotify_encode_fh(dfh, dir, dir_fh_len, hash, 0);
                fanotify_info_set_dir_fh(info, len);
        }
        if (dir2_fh_len) {
                dfh = fanotify_info_dir2_fh(info);
                len = fanotify_encode_fh(dfh, dir2, dir2_fh_len, hash, 0);
                fanotify_info_set_dir2_fh(info, len);
        }
        if (child_fh_len) {
                ffh = fanotify_info_file_fh(info);
                len = fanotify_encode_fh(ffh, child, child_fh_len, hash, 0);
                fanotify_info_set_file_fh(info, len);
        }
        if (name_len) {
                fanotify_info_copy_name(info, name);
                *hash ^= full_name_hash((void *)name_len, name->name, name_len);
        }
        if (name2_len) {
                fanotify_info_copy_name2(info, name2);
                *hash ^= full_name_hash((void *)name2_len, name2->name,
                                        name2_len);
        }

        pr_debug("%s: size=%u dir_fh_len=%u child_fh_len=%u name_len=%u name='%.*s'\n",
                 __func__, size, dir_fh_len, child_fh_len,
                 info->name_len, info->name_len, fanotify_info_name(info));

        if (dir2_fh_len) {
                pr_debug("%s: dir2_fh_len=%u name2_len=%u name2='%.*s'\n",
                         __func__, dir2_fh_len, info->name2_len,
                         info->name2_len, fanotify_info_name2(info));
        }

        return &fne->fae;
}

static struct fanotify_event *fanotify_alloc_error_event(
                                                struct fsnotify_group *group,
                                                __kernel_fsid_t *fsid,
                                                const void *data, int data_type,
                                                unsigned int *hash)
{
        struct fs_error_report *report =
                        fsnotify_data_error_report(data, data_type);
        struct inode *inode;
        struct fanotify_error_event *fee;
        int fh_len;

        if (WARN_ON_ONCE(!report))
                return NULL;

        fee = mempool_alloc(&group->fanotify_data.error_events_pool, GFP_NOFS);
        if (!fee)
                return NULL;

        fee->fae.type = FANOTIFY_EVENT_TYPE_FS_ERROR;
        fee->error = report->error;
        fee->err_count = 1;
        fee->fsid = *fsid;

        inode = report->inode;
        fh_len = fanotify_encode_fh_len(inode);

        /* Bad fh_len. Fallback to using an invalid fh. Should never happen. */
        if (!fh_len && inode)
                inode = NULL;

        fanotify_encode_fh(&fee->object_fh, inode, fh_len, NULL, 0);

        *hash ^= fanotify_hash_fsid(fsid);

        return &fee->fae;
}

static struct fanotify_event *fanotify_alloc_event(
                                struct fsnotify_group *group,
                                u32 mask, const void *data, int data_type,
                                struct inode *dir, const struct qstr *file_name,
                                __kernel_fsid_t *fsid, u32 match_mask)
{
        struct fanotify_event *event = NULL;
        gfp_t gfp = GFP_KERNEL_ACCOUNT;
        unsigned int fid_mode = FAN_GROUP_FLAG(group, FANOTIFY_FID_BITS);
        struct inode *id = fanotify_fid_inode(mask, data, data_type, dir,
                                              fid_mode);
        struct inode *dirid = fanotify_dfid_inode(mask, data, data_type, dir);
        const struct path *path = fsnotify_data_path(data, data_type);
        u64 mnt_id = fsnotify_data_mnt_id(data, data_type);
        struct mem_cgroup *old_memcg;
        struct dentry *moved = NULL;
        struct inode *child = NULL;
        bool name_event = false;
        unsigned int hash = 0;
        bool ondir = mask & FAN_ONDIR;
        struct pid *pid;

        if ((fid_mode & FAN_REPORT_DIR_FID) && dirid) {
                /*
                 * For certain events and group flags, report the child fid
                 * in addition to reporting the parent fid and maybe child name.
                 */
                if (fanotify_report_child_fid(fid_mode, mask) && id != dirid)
                        child = id;

                id = dirid;

                /*
                 * We record file name only in a group with FAN_REPORT_NAME
                 * and when we have a directory inode to report.
                 *
                 * For directory entry modification event, we record the fid of
                 * the directory and the name of the modified entry.
                 *
                 * For event on non-directory that is reported to parent, we
                 * record the fid of the parent and the name of the child.
                 *
                 * Even if not reporting name, we need a variable length
                 * fanotify_name_event if reporting both parent and child fids.
                 */
                if (!(fid_mode & FAN_REPORT_NAME)) {
                        name_event = !!child;
                        file_name = NULL;
                } else if ((mask & ALL_FSNOTIFY_DIRENT_EVENTS) || !ondir) {
                        name_event = true;
                }

                /*
                 * In the special case of FAN_RENAME event, use the match_mask
                 * to determine if we need to report only the old parent+name,
                 * only the new parent+name or both.
                 * 'dirid' and 'file_name' are the old parent+name and
                 * 'moved' has the new parent+name.
                 */
                if (mask & FAN_RENAME) {
                        bool report_old, report_new;

                        if (WARN_ON_ONCE(!match_mask))
                                return NULL;

                        /* Report both old and new parent+name if sb watching */
                        report_old = report_new =
                                match_mask & (1U << FSNOTIFY_ITER_TYPE_SB);
                        report_old |=
                                match_mask & (1U << FSNOTIFY_ITER_TYPE_INODE);
                        report_new |=
                                match_mask & (1U << FSNOTIFY_ITER_TYPE_INODE2);

                        if (!report_old) {
                                /* Do not report old parent+name */
                                dirid = NULL;
                                file_name = NULL;
                        }
                        if (report_new) {
                                /* Report new parent+name */
                                moved = fsnotify_data_dentry(data, data_type);
                        }
                }
        }

        /*
         * For queues with unlimited length lost events are not expected and
         * can possibly have security implications. Avoid losing events when
         * memory is short. For the limited size queues, avoid OOM killer in the
         * target monitoring memcg as it may have security repercussion.
         */
        if (group->max_events == UINT_MAX)
                gfp |= __GFP_NOFAIL;
        else
                gfp |= __GFP_RETRY_MAYFAIL;

        /* Whoever is interested in the event, pays for the allocation. */
        old_memcg = set_active_memcg(group->memcg);

        if (fanotify_is_perm_event(mask)) {
                event = fanotify_alloc_perm_event(data, data_type, gfp);
        } else if (fanotify_is_error_event(mask)) {
                event = fanotify_alloc_error_event(group, fsid, data,
                                                   data_type, &hash);
        } else if (name_event && (file_name || moved || child)) {
                event = fanotify_alloc_name_event(dirid, fsid, file_name, child,
                                                  moved, &hash, gfp);
        } else if (fid_mode) {
                event = fanotify_alloc_fid_event(id, fsid, &hash, gfp);
        } else if (path) {
                event = fanotify_alloc_path_event(path, &hash, gfp);
        } else if (mnt_id) {
                event = fanotify_alloc_mnt_event(mnt_id, gfp);
        } else {
                WARN_ON_ONCE(1);
        }

        if (!event)
                goto out;

        if (FAN_GROUP_FLAG(group, FAN_REPORT_TID))
                pid = get_pid(task_pid(current));
        else
                pid = get_pid(task_tgid(current));

        /* Mix event info, FAN_ONDIR flag and pid into event merge key */
        hash ^= hash_long((unsigned long)pid | ondir, FANOTIFY_EVENT_HASH_BITS);
        fanotify_init_event(event, hash, mask);
        event->pid = pid;

out:
        set_active_memcg(old_memcg);
        return event;
}

/*
 * Get cached fsid of the filesystem containing the object from any mark.
 * All marks are supposed to have the same fsid, but we do not verify that here.
 */
static __kernel_fsid_t fanotify_get_fsid(struct fsnotify_iter_info *iter_info)
{
        struct fsnotify_mark *mark;
        int type;
        __kernel_fsid_t fsid = {};

        fsnotify_foreach_iter_mark_type(iter_info, mark, type) {
                if (!(mark->flags & FSNOTIFY_MARK_FLAG_HAS_FSID))
                        continue;
                fsid = FANOTIFY_MARK(mark)->fsid;
                if (!(mark->flags & FSNOTIFY_MARK_FLAG_WEAK_FSID) &&
                    WARN_ON_ONCE(!fsid.val[0] && !fsid.val[1]))
                        continue;
                return fsid;
        }

        return fsid;
}

/*
 * Add an event to hash table for faster merge.
 */
static void fanotify_insert_event(struct fsnotify_group *group,
                                  struct fsnotify_event *fsn_event)
{
        struct fanotify_event *event = FANOTIFY_E(fsn_event);
        unsigned int bucket = fanotify_event_hash_bucket(group, event);
        struct hlist_head *hlist = &group->fanotify_data.merge_hash[bucket];

        assert_spin_locked(&group->notification_lock);

        if (!fanotify_is_hashed_event(event->mask))
                return;

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

        hlist_add_head(&event->merge_list, hlist);
}

static int fanotify_handle_event(struct fsnotify_group *group, u32 mask,
                                 const void *data, int data_type,
                                 struct inode *dir,
                                 const struct qstr *file_name, u32 cookie,
                                 struct fsnotify_iter_info *iter_info)
{
        int ret = 0;
        struct fanotify_event *event;
        struct fsnotify_event *fsn_event;
        __kernel_fsid_t fsid = {};
        u32 match_mask = 0;

        BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
        BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
        BUILD_BUG_ON(FAN_ATTRIB != FS_ATTRIB);
        BUILD_BUG_ON(FAN_CLOSE_NOWRITE != FS_CLOSE_NOWRITE);
        BUILD_BUG_ON(FAN_CLOSE_WRITE != FS_CLOSE_WRITE);
        BUILD_BUG_ON(FAN_OPEN != FS_OPEN);
        BUILD_BUG_ON(FAN_MOVED_TO != FS_MOVED_TO);
        BUILD_BUG_ON(FAN_MOVED_FROM != FS_MOVED_FROM);
        BUILD_BUG_ON(FAN_CREATE != FS_CREATE);
        BUILD_BUG_ON(FAN_DELETE != FS_DELETE);
        BUILD_BUG_ON(FAN_DELETE_SELF != FS_DELETE_SELF);
        BUILD_BUG_ON(FAN_MOVE_SELF != FS_MOVE_SELF);
        BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
        BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
        BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
        BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
        BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);
        BUILD_BUG_ON(FAN_OPEN_EXEC != FS_OPEN_EXEC);
        BUILD_BUG_ON(FAN_OPEN_EXEC_PERM != FS_OPEN_EXEC_PERM);
        BUILD_BUG_ON(FAN_FS_ERROR != FS_ERROR);
        BUILD_BUG_ON(FAN_RENAME != FS_RENAME);
        BUILD_BUG_ON(FAN_PRE_ACCESS != FS_PRE_ACCESS);

        BUILD_BUG_ON(HWEIGHT32(ALL_FANOTIFY_EVENT_BITS) != 24);

        mask = fanotify_group_event_mask(group, iter_info, &match_mask,
                                         mask, data, data_type, dir);
        if (!mask)
                return 0;

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

        if (fanotify_is_perm_event(mask)) {
                /*
                 * fsnotify_prepare_user_wait() fails if we race with mark
                 * deletion.  Just let the operation pass in that case.
                 */
                if (!fsnotify_prepare_user_wait(iter_info))
                        return 0;
        }

        if (FAN_GROUP_FLAG(group, FANOTIFY_FID_BITS))
                fsid = fanotify_get_fsid(iter_info);

        event = fanotify_alloc_event(group, mask, data, data_type, dir,
                                     file_name, &fsid, match_mask);
        ret = -ENOMEM;
        if (unlikely(!event)) {
                /*
                 * We don't queue overflow events for permission events as
                 * there the access is denied and so no event is in fact lost.
                 */
                if (!fanotify_is_perm_event(mask))
                        fsnotify_queue_overflow(group);
                goto finish;
        }

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

                ret = 0;
        } else if (fanotify_is_perm_event(mask)) {
                ret = fanotify_get_response(group, FANOTIFY_PERM(event),
                                            iter_info);
        }
finish:
        if (fanotify_is_perm_event(mask))
                fsnotify_finish_user_wait(iter_info);

        return ret;
}

static void fanotify_free_group_priv(struct fsnotify_group *group)
{
        put_user_ns(group->user_ns);
        kfree(group->fanotify_data.merge_hash);
        if (group->fanotify_data.ucounts)
                dec_ucount(group->fanotify_data.ucounts,
                           UCOUNT_FANOTIFY_GROUPS);

        if (mempool_initialized(&group->fanotify_data.error_events_pool))
                mempool_exit(&group->fanotify_data.error_events_pool);
}

static void fanotify_free_path_event(struct fanotify_event *event)
{
        path_put(fanotify_event_path(event));
        kmem_cache_free(fanotify_path_event_cachep, FANOTIFY_PE(event));
}

static void fanotify_free_perm_event(struct fanotify_event *event)
{
        path_put(fanotify_event_path(event));
        kmem_cache_free(fanotify_perm_event_cachep, FANOTIFY_PERM(event));
}

static void fanotify_free_fid_event(struct fanotify_event *event)
{
        struct fanotify_fid_event *ffe = FANOTIFY_FE(event);

        if (fanotify_fh_has_ext_buf(&ffe->object_fh))
                kfree(fanotify_fh_ext_buf(&ffe->object_fh));
        kmem_cache_free(fanotify_fid_event_cachep, ffe);
}

static void fanotify_free_name_event(struct fanotify_event *event)
{
        kfree(FANOTIFY_NE(event));
}

static void fanotify_free_error_event(struct fsnotify_group *group,
                                      struct fanotify_event *event)
{
        struct fanotify_error_event *fee = FANOTIFY_EE(event);

        mempool_free(fee, &group->fanotify_data.error_events_pool);
}

static void fanotify_free_mnt_event(struct fanotify_event *event)
{
        kmem_cache_free(fanotify_mnt_event_cachep, FANOTIFY_ME(event));
}

static void fanotify_free_event(struct fsnotify_group *group,
                                struct fsnotify_event *fsn_event)
{
        struct fanotify_event *event;

        event = FANOTIFY_E(fsn_event);
        put_pid(event->pid);
        switch (event->type) {
        case FANOTIFY_EVENT_TYPE_PATH:
                fanotify_free_path_event(event);
                break;
        case FANOTIFY_EVENT_TYPE_PATH_PERM:
                fanotify_free_perm_event(event);
                break;
        case FANOTIFY_EVENT_TYPE_FID:
                fanotify_free_fid_event(event);
                break;
        case FANOTIFY_EVENT_TYPE_FID_NAME:
                fanotify_free_name_event(event);
                break;
        case FANOTIFY_EVENT_TYPE_OVERFLOW:
                kfree(event);
                break;
        case FANOTIFY_EVENT_TYPE_FS_ERROR:
                fanotify_free_error_event(group, event);
                break;
        case FANOTIFY_EVENT_TYPE_MNT:
                fanotify_free_mnt_event(event);
                break;
        default:
                WARN_ON_ONCE(1);
        }
}

static void fanotify_freeing_mark(struct fsnotify_mark *mark,
                                  struct fsnotify_group *group)
{
        if (!FAN_GROUP_FLAG(group, FAN_UNLIMITED_MARKS))
                dec_ucount(group->fanotify_data.ucounts, UCOUNT_FANOTIFY_MARKS);
}

static void fanotify_free_mark(struct fsnotify_mark *fsn_mark)
{
        kmem_cache_free(fanotify_mark_cache, FANOTIFY_MARK(fsn_mark));
}

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