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/fs_context.h>
#include <linux/fs_parser.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/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;
static unsigned int debugfs_allow __ro_after_init = DEFAULT_DEBUGFS_ALLOW_BITS;

/*
 * 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 mnt_idmap *idmap,
			   struct dentry *dentry, struct iattr *ia)
{
	int ret;

	if (ia->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)) {
		ret = security_locked_down(LOCKDOWN_DEBUGFS);
		if (ret)
			return ret;
	}
	return simple_setattr(&nop_mnt_idmap, 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();
		simple_inode_init_ts(inode);
	}
	return inode;
}

struct debugfs_fs_info {
	kuid_t uid;
	kgid_t gid;
	umode_t mode;
	/* Opt_* bitfield. */
	unsigned int opts;
};

enum {
	Opt_uid,
	Opt_gid,
	Opt_mode,
};

static const struct fs_parameter_spec debugfs_param_specs[] = {
	fsparam_u32	("gid",		Opt_gid),
	fsparam_u32oct	("mode",	Opt_mode),
	fsparam_u32	("uid",		Opt_uid),
	{}
};

static int debugfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
{
	struct debugfs_fs_info *opts = fc->s_fs_info;
	struct fs_parse_result result;
	kuid_t uid;
	kgid_t gid;
	int opt;

	opt = fs_parse(fc, debugfs_param_specs, param, &result);
	if (opt < 0) {
		/*
                * We might like to report bad mount options here; but
                * traditionally debugfs has ignored all mount options
                */
		if (opt == -ENOPARAM)
			return 0;

		return opt;
	}

	switch (opt) {
	case Opt_uid:
		uid = make_kuid(current_user_ns(), result.uint_32);
		if (!uid_valid(uid))
			return invalf(fc, "Unknown uid");
		opts->uid = uid;
		break;
	case Opt_gid:
		gid = make_kgid(current_user_ns(), result.uint_32);
		if (!gid_valid(gid))
			return invalf(fc, "Unknown gid");
		opts->gid = gid;
		break;
	case Opt_mode:
		opts->mode = result.uint_32 & S_IALLUGO;
		break;
	/*
	 * We might like to report bad mount options here;
	 * but traditionally debugfs has ignored all mount options
	 */
	}

	opts->opts |= BIT(opt);

	return 0;
}

static void _debugfs_apply_options(struct super_block *sb, bool remount)
{
	struct debugfs_fs_info *fsi = sb->s_fs_info;
	struct inode *inode = d_inode(sb->s_root);

	/*
	 * On remount, only reset mode/uid/gid if they were provided as mount
	 * options.
	 */

	if (!remount || fsi->opts & BIT(Opt_mode)) {
		inode->i_mode &= ~S_IALLUGO;
		inode->i_mode |= fsi->mode;
	}

	if (!remount || fsi->opts & BIT(Opt_uid))
		inode->i_uid = fsi->uid;

	if