inode.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  inode.c - securityfs
 *
 *  Copyright (C) 2005 Greg Kroah-Hartman <[email protected]>
 *
 *  Based on fs/debugfs/inode.c which had the following copyright notice:
 *    Copyright (C) 2004 Greg Kroah-Hartman <[email protected]>
 *    Copyright (C) 2004 IBM Inc.
 */

/* #define DEBUG */
#include <linux/sysfs.h>
#include <linux/kobject.h>
#include <linux/fs.h>
#include <linux/fs_context.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>

#include "lsm.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 securityfs_fill_super(struct super_block *sb, struct fs_context *fc)
{
	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 int securityfs_get_tree(struct fs_context *fc)
{
	return get_tree_single(fc, securityfs_fill_super);
}

static const struct fs_context_operations securityfs_context_ops = {
	.get_tree	= securityfs_get_tree,
};

static int securityfs_init_fs_context(struct fs_context *fc)
{
	fc->ops = &securityfs_context_ops;
	return 0;
}

static struct file_system_type fs_type = {
	.owner =	THIS_MODULE,
	.name =		"securityfs",
	.init_fs_context = securityfs_init_fs_context,
	.kill_sb =	kill_anon_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;
	bool pinned = false;

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

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

	if (!parent) {
		error = simple_pin_fs(&fs_type, &mount, &mount_count);
		if (error)
			return ERR_PTR(error);
		pinned = true;
		parent = mount->mnt_root;
	}

	inode = new_inode(parent->d_sb);
	if (unlikely(!inode)) {
		dentry = ERR_PTR(-ENOMEM);
		goto out;
	}

	dir = d_inode(parent);

	dentry = simple_start_creating(parent, name);
	if (IS_ERR(dentry)) {
		iput(inode);
		goto out;
	}
	inode->i_ino = get_next_ino();
	inode->i_mode = mode;
	simple_inode_init_ts(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_make_persistent(dentry, inode);
	simple_done_creating(dentry);
	return dentry; // borrowed

out:
	if (pinned)
		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);

static void remove_one(struct dentry *victim)
{
	if (victim->d_parent == victim->d_sb->s_root)
		simple_release_fs(&mount, &mount_count);
}

/**
 * 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.
 *
 * AV: when applied to directory it will take all children out; no need to call
 * it for descendents if ancestor is getting killed.
 */
void securityfs_remove(struct dentry *dentry)
{
	if (IS_ERR_OR_NULL(dentry))
		return;

	simple_pin_fs(&fs_type, &mount, &mount_count);
	simple_recursive_removal(dentry, remove_one);
	simple_release_fs(&mount, &mount_count);
}
EXPORT_SYMBOL_GPL(securityfs_remove);

#ifdef CONFIG_SECURITY
#include <linux/spinlock.h>

static struct dentry *lsm_dentry;

static ssize_t lsm_read(struct file *filp, char __user *buf, size_t count,
			loff_t *ppos)
{
	int i;
	static char *str;
	static size_t len;
	static DEFINE_SPINLOCK(lock);

	/* NOTE: we never free or modify the string once it is set */

	if (unlikely(!str || !len)) {
		char *str_tmp;
		size_t len_tmp = 0;

		for (i = 0; i < lsm_active_cnt; i++)
			/* the '+ 1' accounts for either a comma or a NUL */
			len_tmp += strlen(lsm_idlist[i]->name) + 1;

		str_tmp = kmalloc(len_tmp, GFP_KERNEL);
		if (!str_tmp)
			return -ENOMEM;
		str_tmp[0] = '\0';

		for (i = 0; i < lsm_active_cnt; i++) {
			if (i > 0)
				strcat(str_tmp, ",");
			strcat(str_tmp, lsm_idlist[i]->name);
		}

		spin_lock(&lock);
		if (!str) {
			str = str_tmp;
			len = len_tmp - 1;
		} else
			kfree(str_tmp);
		spin_unlock(&lock);
	}

	return simple_read_from_buffer(buf, count, ppos, str, len);
}

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

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;
}