// SPDX-License-Identifier: GPL-2.0-only
/*
 *  inode.c - securityfs
 *
 *  Copyright (C) 2005 Greg Kroah-Hartman <gregkh@suse.de>
 *
 *  Based on fs/debugfs/inode.c which had the following copyright notice:
 *    Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
 *    Copyright (C) 2004 IBM Inc.
 */

/* #define DEBUG */
#include <linux/sysfs.h>
#include <linux/kobject.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/pagemap.h>
#include <linux/init.h>
#include <linux/namei.h>
#include <linux/security.h>
#include <linux/lsm_hooks.h>
#include <linux/magic.h>

static struct vfsmount *mount;
static int mount_count;

static void securityfs_free_inode(struct inode *inode)
{
        if (S_ISLNK(inode->i_mode))
                kfree(inode->i_link);
        free_inode_nonrcu(inode);
}

static const struct super_operations securityfs_super_operations = {
        .statfs         = simple_statfs,
        .free_inode     = securityfs_free_inode,
};

static int fill_super(struct super_block *sb, void *data, int silent)
{
        static const struct tree_descr files[] = {{""}};
        int error;

        error = simple_fill_super(sb, SECURITYFS_MAGIC, files);
        if (error)
                return error;

        sb->s_op = &securityfs_super_operations;

        return 0;
}

static struct dentry *get_sb(struct file_system_type *fs_type,
                  int flags, const char *dev_name,
                  void *data)
{
        return mount_single(fs_type, flags, data, fill_super);
}

static struct file_system_type fs_type = {
        .owner =        THIS_MODULE,
        .name =         "securityfs",
        .mount =        get_sb,
        .kill_sb =      kill_litter_super,
};

/**
 * securityfs_create_dentry - create a dentry in the securityfs filesystem
 *
 * @name: a pointer to a string containing the name of the file to create.
 * @mode: the permission that the file should have
 * @parent: a pointer to the parent dentry for this file.  This should be a
 *          directory dentry if set.  If this parameter is %NULL, then the
 *          file will be created in the root of the securityfs filesystem.
 * @data: a pointer to something that the caller will want to get to later
 *        on.  The inode.i_private pointer will point to this value on
 *        the open() call.
 * @fops: a pointer to a struct file_operations that should be used for
 *        this file.
 * @iops: a point to a struct of inode_operations that should be used for
 *        this file/dir
 *
 * This is the basic "create a file/dir/symlink" function for
 * securityfs.  It allows for a wide range of flexibility in creating
 * a file, or a directory (if you want to create a directory, the
 * securityfs_create_dir() function is recommended to be used
 * instead).
 *
 * This function returns a pointer to a dentry if it succeeds.  This
 * pointer must be passed to the securityfs_remove() function when the
 * file is to be removed (no automatic cleanup happens if your module
 * is unloaded, you are responsible here).  If an error occurs, the
 * function will return the error value (via ERR_PTR).
 *
 * If securityfs is not enabled in the kernel, the value %-ENODEV is
 * returned.
 */
static struct dentry *securityfs_create_dentry(const char *name, umode_t mode,
                                        struct dentry *parent, void *data,
                                        const struct file_operations *fops,
                                        const struct inode_operations *iops)
{
        struct dentry *dentry;
        struct inode *dir, *inode;
        int error;

        if (!(mode & S_IFMT))
                mode = (mode & S_IALLUGO) | S_IFREG;

        pr_debug("securityfs: creating file '%s'\n",name);

        error = simple_pin_fs(&fs_type, &mount, &mount_count);
        if (error)
                return ERR_PTR(error);

        if (!parent)
                parent = mount->mnt_root;

        dir = d_inode(parent);

        inode_lock(dir);
        dentry = lookup_one_len(name, parent, strlen(name));
        if (IS_ERR(dentry))
                goto out;

        if (d_really_is_positive(dentry)) {
                error = -EEXIST;
                goto out1;
        }

        inode = new_inode(dir->i_sb);
        if (!inode) {
                error = -ENOMEM;
                goto out1;
        }

        inode->i_ino = get_next_ino();
        inode->i_mode = mode;
        inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
        inode->i_private = data;
        if (S_ISDIR(mode)) {
                inode->i_op = &simple_dir_inode_operations;
                inode->i_fop = &simple_dir_operations;
                inc_nlink(inode);
                inc_nlink(dir);
        } else if (S_ISLNK(mode)) {
                inode->i_op = iops ? iops : &simple_symlink_inode_operations;
                inode->i_link = data;
        } else {
                inode->i_fop = fops;
        }
        d_instantiate(dentry, inode);
        dget(dentry);
        inode_unlock(dir);
        return dentry;

out1:
        dput(dentry);
        dentry = ERR_PTR(error);
out:
        inode_unlock(dir);
        simple_release_fs(&mount, &mount_count);
        return dentry;
}

/**
 * securityfs_create_file - create a file in the securityfs filesystem
 *
 * @name: a pointer to a string containing the name of the file to create.
 * @mode: the permission that the file should have
 * @parent: a pointer to the parent dentry for this file.  This should be a
 *          directory dentry if set.  If this parameter is %NULL, then the
 *          file will be created in the root of the securityfs filesystem.
 * @data: a pointer to something that the caller will want to get to later
 *        on.  The inode.i_private pointer will point to this value on
 *        the open() call.
 * @fops: a pointer to a struct file_operations that should be used for
 *        this file.
 *
 * This function creates a file in securityfs with the given @name.
 *
 * This function returns a pointer to a dentry if it succeeds.  This
 * pointer must be passed to the securityfs_remove() function when the file is
 * to be removed (no automatic cleanup happens if your module is unloaded,
 * you are responsible here).  If an error occurs, the function will return
 * the error value (via ERR_PTR).
 *
 * If securityfs is not enabled in the kernel, the value %-ENODEV is
 * returned.
 */
struct dentry *securityfs_create_file(const char *name, umode_t mode,
                                      struct dentry *parent, void *data,
                                      const struct file_operations *fops)
{
        return securityfs_create_dentry(name, mode, parent, data, fops, NULL);
}
EXPORT_SYMBOL_GPL(securityfs_create_file);

/**
 * securityfs_create_dir - create a directory in the securityfs filesystem
 *
 * @name: a pointer to a string containing the name of the directory to
 *        create.
 * @parent: a pointer to the parent dentry for this file.  This should be a
 *          directory dentry if set.  If this parameter is %NULL, then the
 *          directory will be created in the root of the securityfs filesystem.
 *
 * This function creates a directory in securityfs with the given @name.
 *
 * This function returns a pointer to a dentry if it succeeds.  This
 * pointer must be passed to the securityfs_remove() function when the file is
 * to be removed (no automatic cleanup happens if your module is unloaded,
 * you are responsible here).  If an error occurs, the function will return
 * the error value (via ERR_PTR).
 *
 * If securityfs is not enabled in the kernel, the value %-ENODEV is
 * returned.
 */
struct dentry *securityfs_create_dir(const char *name, struct dentry *parent)
{
        return securityfs_create_file(name, S_IFDIR | 0755, parent, NULL, NULL);
}
EXPORT_SYMBOL_GPL(securityfs_create_dir);

/**
 * securityfs_create_symlink - create a symlink in the securityfs filesystem
 *
 * @name: a pointer to a string containing the name of the symlink to
 *        create.
 * @parent: a pointer to the parent dentry for the symlink.  This should be a
 *          directory dentry if set.  If this parameter is %NULL, then the
 *          directory will be created in the root of the securityfs filesystem.
 * @target: a pointer to a string containing the name of the symlink's target.
 *          If this parameter is %NULL, then the @iops parameter needs to be
 *          setup to handle .readlink and .get_link inode_operations.
 * @iops: a pointer to the struct inode_operations to use for the symlink. If
 *        this parameter is %NULL, then the default simple_symlink_inode
 *        operations will be used.
 *
 * This function creates a symlink in securityfs with the given @name.
 *
 * This function returns a pointer to a dentry if it succeeds.  This
 * pointer must be passed to the securityfs_remove() function when the file is
 * to be removed (no automatic cleanup happens if your module is unloaded,
 * you are responsible here).  If an error occurs, the function will return
 * the error value (via ERR_PTR).
 *
 * If securityfs is not enabled in the kernel, the value %-ENODEV is
 * returned.
 */
struct dentry *securityfs_create_symlink(const char *name,
                                         struct dentry *parent,
                                         const char *target,
                                         const struct inode_operations *iops)
{
        struct dentry *dent;
        char *link = NULL;

        if (target) {
                link = kstrdup(target, GFP_KERNEL);
                if (!link)
                        return ERR_PTR(-ENOMEM);
        }
        dent = securityfs_create_dentry(name, S_IFLNK | 0444, parent,
                                        link, NULL, iops);
        if (IS_ERR(dent))
                kfree(link);

        return dent;
}
EXPORT_SYMBOL_GPL(securityfs_create_symlink);

/**
 * securityfs_remove - removes a file or directory from the securityfs filesystem
 *
 * @dentry: a pointer to a the dentry of the file or directory to be removed.
 *
 * This function removes a file or directory in securityfs that was previously
 * created with a call to another securityfs function (like
 * securityfs_create_file() or variants thereof.)
 *
 * This function is required to be called in order for the file to be
 * removed. No automatic cleanup of files will happen when a module is
 * removed; you are responsible here.
 */
void securityfs_remove(struct dentry *dentry)
{
        struct inode *dir;

        if (!dentry || IS_ERR(dentry))
                return;

        dir = d_inode(dentry->d_parent);
        inode_lock(dir);
        if (simple_positive(dentry)) {
                if (d_is_dir(dentry))
                        simple_rmdir(dir, dentry);
                else
                        simple_unlink(dir, dentry);
                dput(dentry);
        }
        inode_unlock(dir);
        simple_release_fs(&mount, &mount_count);
}
EXPORT_SYMBOL_GPL(securityfs_remove);

#ifdef CONFIG_SECURITY
static struct dentry *lsm_dentry;
static ssize_t lsm_read(struct file *filp, char __user *buf, size_t count,
                        loff_t *ppos)
{
        return simple_read_from_buffer(buf, count, ppos, lsm_names,
                strlen(lsm_names));
}

static const struct file_operations lsm_ops = {
        .read = lsm_read,
        .llseek = generic_file_llseek,
};
#endif

static int __init securityfs_init(void)
{
        int retval;

        retval = sysfs_create_mount_point(kernel_kobj, "security");
        if (retval)
                return retval;

        retval = register_filesystem(&fs_type);
        if (retval) {
                sysfs_remove_mount_point(kernel_kobj, "security");
                return retval;
        }
#ifdef CONFIG_SECURITY
        lsm_dentry = securityfs_create_file("lsm", 0444, NULL, NULL,
                                                &lsm_ops);
#endif
        return 0;
}
core_initcall(securityfs_init);