path: root/fs/debugfs/inode.c

// SPDX-License-Identifier: GPL-2.0
/*
 *  inode.c - part of debugfs, a tiny little debug file system
 *
 *  Copyright (C) 2004,2019 Greg Kroah-Hartman <greg@kroah.com>
 *  Copyright (C) 2004 IBM Inc.
 *  Copyright (C) 2019 Linux Foundation <gregkh@linuxfoundation.org>
 *
 *  debugfs is for people to use instead of /proc or /sys.
 *  See ./Documentation/core-api/kernel-api.rst for more details.
 */

#define pr_fmt(fmt)	"debugfs: " fmt

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/pagemap.h>
#include <linux/init.h>
#include <linux/kobject.h>
#include <linux/namei.h>
#include <linux/debugfs.h>
#include <linux/fsnotify.h>
#include <linux/string.h>
#include <linux/seq_file.h>
#include <linux/parser.h>
#include <linux/magic.h>
#include <linux/slab.h>
#include <linux/security.h>

#include "internal.h"

#define DEBUGFS_DEFAULT_MODE	0700

static struct vfsmount *debugfs_mount;
static int debugfs_mount_count;
static bool debugfs_registered;

/*
 * Don't allow access attributes to be changed whilst the kernel is locked down
 * so that we can use the file mode as part of a heuristic to determine whether
 * to lock down individual files.
 */
static int debugfs_setattr(struct dentry *dentry, struct iattr *ia)
{
	int ret = security_locked_down(LOCKDOWN_DEBUGFS);

	if (ret && (ia->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
		return ret;
	return simple_setattr(dentry, ia);
}

static const struct inode_operations debugfs_file_inode_operations = {
	.setattr	= debugfs_setattr,
};
static const struct inode_operations debugfs_dir_inode_operations = {
	.lookup		= simple_lookup,
	.setattr	= debugfs_setattr,
};
static const struct inode_operations debugfs_symlink_inode_operations = {
	.get_link	= simple_get_link,
	.setattr	= debugfs_setattr,
};

static struct inode *debugfs_get_inode(struct super_block *sb)
{
	struct inode *inode = new_inode(sb);
	if (inode) {
		inode->i_ino = get_next_ino();
		inode->i_atime = inode->i_mtime =
			inode->i_ctime = current_time(inode);
	}
	return inode;
}

struct debugfs_mount_opts {
	kuid_t uid;
	kgid_t gid;
	umode_t mode;
};

enum {
	Opt_uid,
	Opt_gid,
	Opt_mode,
	Opt_err
};

static const match_table_t tokens = {
	{Opt_uid, "uid=%u"},
	{Opt_gid, "gid=%u"},
	{Opt_mode, "mode=%o"},
	{Opt_err, NULL}
};

struct debugfs_fs_info {
	struct debugfs_mount_opts mount_opts;
};

static int debugfs_parse_options(char *data, struct debugfs_mount_opts *opts)
{
	substring_t args[MAX_OPT_ARGS];
	int option;
	int token;
	kuid_t uid;
	kgid_t gid;
	char *p;

	opts->mode = DEBUGFS_DEFAULT_MODE;

	while ((p = strsep(&data, ",")) != NULL) {
		if (!*p)
			continue;

		token = match_token(p, tokens, args);
		switch (token) {
		case Opt_uid:
			if (match_int(&args[0], &option))
				return -EINVAL;
			uid = make_kuid(current_user_ns(), option);
			if (!uid_valid(uid))
				return -EINVAL;
			opts->uid = uid;
			break;
		case Opt_gid:
			if (match_int(&args[0], &option))
				return -EINVAL;
			gid = make_kgid(current_user_ns(), option);
			if (!gid_valid(gid))
				return -EINVAL;
			opts->gid = gid;
			break;
		case Opt_mode:
			if (match_octal(&args[0], &option))
				return -EINVAL;
			opts->mode = option & S_IALLUGO;
			break;
		/*
		 * We might like to report bad mount options here;
		 * but traditionally debugfs has ignored all mount options
		 */
		}
	}

	return 0;
}

static int debugfs_apply_options(struct super_block *sb)
{
	struct debugfs_fs_info *fsi = sb->s_fs_info;
	struct inode *inode = d_inode(sb->s_root);
	struct debugfs_mount_opts *opts = &fsi->mount_opts;

	inode->i_mode &= ~S_IALLUGO;
	inode->i_mode |= opts->mode;

	inode->i_uid = opts->uid;
	inode->i_gid = opts->gid;

	return 0;
}

static int debugfs_remount(struct super_block *sb, int *flags, char *data)
{
	int err;
	struct debugfs_fs_info *fsi = sb->s_fs_info;

	sync_filesystem(sb);
	err = debugfs_parse_options(data, &fsi->mount_opts);
	if (err)
		goto fail;

	debugfs_apply_options(sb);

fail:
	return err