internal/pathrs/mkdirall_pathrslite.go

// SPDX-License-Identifier: Apache-2.0
/*
 * Copyright (C) 2024-2025 Aleksa Sarai <cyphar@cyphar.com>
 * Copyright (C) 2024-2025 SUSE LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package pathrs

import (
	"fmt"
	"os"
	"path/filepath"

	"github.com/cyphar/filepath-securejoin/pathrs-lite"
	"github.com/sirupsen/logrus"
	"golang.org/x/sys/unix"
)

// MkdirAllInRootOpen attempts to make
//
//	path, _ := securejoin.SecureJoin(root, unsafePath)
//	os.MkdirAll(path, mode)
//	os.Open(path)
//
// safer against attacks where components in the path are changed between
// SecureJoin returning and MkdirAll (or Open) being called. In particular, we
// try to detect any symlink components in the path while we are doing the
// MkdirAll.
//
// NOTE: If unsafePath is a subpath of root, we assume that you have already
// called SecureJoin and so we use the provided path verbatim without resolving
// any symlinks (this is done in a way that avoids symlink-exchange races).
// This means that the path also must not contain ".." elements, otherwise an
// error will occur.
//
// This uses (pathrs-lite).MkdirAllHandle under the hood, but it has special
// handling if unsafePath has already been scoped within the rootfs (this is
// needed for a lot of runc callers and fixing this would require reworking a
// lot of path logic).
func MkdirAllInRootOpen(root, unsafePath string, mode os.FileMode) (*os.File, error) {
	// If the path is already "within" the root, get the path relative to the
	// root and use that as the unsafe path. This is necessary because a lot of
	// MkdirAllInRootOpen callers have already done SecureJoin, and refactoring
	// all of them to stop using these SecureJoin'd paths would require a fair
	// amount of work.
	// TODO(cyphar): Do the refactor to libpathrs once it's ready.
	if IsLexicallyInRoot(root, unsafePath) {
		subPath, err := filepath.Rel(root, unsafePath)
		if err != nil {
			return nil, err
		}
		unsafePath = subPath
	}

	// Check for any silly mode bits.
	if mode&^0o7777 != 0 {
		return nil, fmt.Errorf("tried to include non-mode bits in MkdirAll mode: 0o%.3o", mode)
	}
	// Linux (and thus os.MkdirAll) silently ignores the suid and sgid bits if
	// passed. While it would make sense to return an error in that case (since
	// the user has asked for a mode that won't be applied), for compatibility
	// reasons we have to ignore these bits.
	if ignoredBits := mode &^ 0o1777; ignoredBits != 0 {
		logrus.Warnf("MkdirAll called with no-op mode bits that are ignored by Linux: 0o%.3o", ignoredBits)
		mode &= 0o1777
	}

	rootDir, err := os.OpenFile(root, unix.O_DIRECTORY|unix.O_CLOEXEC, 0)
	if err != nil {
		return nil, fmt.Errorf("open root handle: %w", err)
	}
	defer rootDir.Close()

	return retryEAGAIN(func() (*os.File, error) {
		return pathrs.MkdirAllHandle(rootDir, unsafePath, mode)
	})
}

// MkdirAllInRoot is a wrapper around MkdirAllInRootOpen which closes the
// returned handle, for callers that don't need to use it.
func MkdirAllInRoot(root, unsafePath string, mode os.FileMode) error {
	f, err := MkdirAllInRootOpen(root, unsafePath, mode)
	if err == nil {
		_ = f.Close()
	}
	return err
}