// SPDX-License-Identifier: GPL-2.0
/*
 * fs/sysfs/symlink.c - operations for initializing and mounting sysfs
 *
 * Copyright (c) 2001-3 Patrick Mochel
 * Copyright (c) 2007 SUSE Linux Products GmbH
 * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
 *
 * Please see Documentation/filesystems/sysfs.rst for more information.
 */

#include <linux/fs.h>
#include <linux/magic.h>
#include <linux/mount.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/user_namespace.h>
#include <linux/fs_context.h>
#include <net/net_namespace.h>

#include "sysfs.h"

static struct kernfs_root *sysfs_root;
struct kernfs_node *sysfs_root_kn;

static int sysfs_get_tree(struct fs_context *fc)
{
        struct kernfs_fs_context *kfc = fc->fs_private;
        int ret;

        ret = kernfs_get_tree(fc);
        if (ret)
                return ret;

        if (kfc->new_sb_created)
                fc->root->d_sb->s_iflags |= SB_I_USERNS_VISIBLE;
        return 0;
}

static void sysfs_fs_context_free(struct fs_context *fc)
{
        struct kernfs_fs_context *kfc = fc->fs_private;

        if (kfc->ns_tag)
                kobj_ns_drop(KOBJ_NS_TYPE_NET, kfc->ns_tag);
        kernfs_free_fs_context(fc);
        kfree(kfc);
}

static const struct fs_context_operations sysfs_fs_context_ops = {
        .free           = sysfs_fs_context_free,
        .get_tree       = sysfs_get_tree,
};

static int sysfs_init_fs_context(struct fs_context *fc)
{
        struct kernfs_fs_context *kfc;
        struct net *netns;

        if (!(fc->sb_flags & SB_KERNMOUNT)) {
                if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET))
                        return -EPERM;
        }

        kfc = kzalloc_obj(struct kernfs_fs_context);
        if (!kfc)
                return -ENOMEM;

        kfc->ns_tag = netns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
        kfc->root = sysfs_root;
        kfc->magic = SYSFS_MAGIC;
        fc->fs_private = kfc;
        fc->ops = &sysfs_fs_context_ops;
        if (netns) {
                put_user_ns(fc->user_ns);
                fc->user_ns = get_user_ns(netns->user_ns);
        }
        fc->global = true;
        return 0;
}

static void sysfs_kill_sb(struct super_block *sb)
{
        void *ns = (void *)kernfs_super_ns(sb);

        kernfs_kill_sb(sb);
        kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
}

static struct file_system_type sysfs_fs_type = {
        .name                   = "sysfs",
        .init_fs_context        = sysfs_init_fs_context,
        .kill_sb                = sysfs_kill_sb,
        .fs_flags               = FS_USERNS_MOUNT,
};

int __init sysfs_init(void)
{
        int err;

        sysfs_root = kernfs_create_root(NULL, KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK,
                                        NULL);
        if (IS_ERR(sysfs_root))
                return PTR_ERR(sysfs_root);

        sysfs_root_kn = kernfs_root_to_node(sysfs_root);

        err = register_filesystem(&sysfs_fs_type);
        if (err) {
                kernfs_destroy_root(sysfs_root);
                return err;
        }

        return 0;
}