mirror of
https://github.com/opencontainers/runc.git
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Aleksa Sarai
d0ff22b574
In order to maintain compatibility with previous releases of runc (which permitted dangling symlinks as path components by permitting non-existent path components to be treated like real directories) we have to first do SecureJoin to construct a target path that is compatible with the old behaviour but has all dangling symlinks (or other invalid paths like ".." components after non-existent directories) removed. This is effectively a more generic verison of commit3f925525b4("rootfs: re-allow dangling symlinks in mount targets") and will let us remove the need for open-coding SecureJoin workarounds. Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> (cherry picked from commitcfb74326be) Signed-off-by: Aleksa Sarai <aleksa@amutable.com>
78 lines
2.5 KiB
Go
78 lines
2.5 KiB
Go
// SPDX-License-Identifier: Apache-2.0
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/*
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* Copyright (C) 2024-2025 Aleksa Sarai <cyphar@cyphar.com>
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* Copyright (C) 2024-2025 SUSE LLC
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package pathrs
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import (
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"fmt"
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"os"
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"path/filepath"
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"github.com/cyphar/filepath-securejoin/pathrs-lite"
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"golang.org/x/sys/unix"
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)
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// OpenInRoot opens the given path inside the root with the provided flags. It
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// is effectively shorthand for [securejoin.OpenInRoot] followed by
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// [securejoin.Reopen].
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func OpenInRoot(root, subpath string, flags int) (*os.File, error) {
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handle, err := retryEAGAIN(func() (*os.File, error) {
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return pathrs.OpenInRoot(root, subpath)
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})
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if err != nil {
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return nil, err
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}
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defer handle.Close()
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return Reopen(handle, flags)
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}
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// CreateInRoot creates a new file inside a root (as well as any missing parent
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// directories) and returns a handle to said file. This effectively has
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// open(O_CREAT|O_NOFOLLOW) semantics. If you want the creation to use O_EXCL,
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// include it in the passed flags. The fileMode argument uses unix.* mode bits,
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// *not* os.FileMode.
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func CreateInRoot(root, subpath string, flags int, fileMode uint32) (*os.File, error) {
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subpath, err := hallucinateUnsafePath(root, subpath)
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if err != nil {
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return nil, fmt.Errorf("failed to construct hallucinated target path: %w", err)
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}
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dir, filename := filepath.Split(subpath)
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if filepath.Join("/", filename) == "/" {
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return nil, fmt.Errorf("create in root subpath %q has bad trailing component %q", subpath, filename)
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}
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dirFd, err := MkdirAllInRoot(root, dir, 0o755)
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if err != nil {
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return nil, err
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}
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defer dirFd.Close()
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// We know that the filename does not have any "/" components, and that
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// dirFd is inside the root. O_NOFOLLOW will stop us from following
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// trailing symlinks, so this is safe to do. libpathrs's Root::create_file
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// works the same way.
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flags |= unix.O_CREAT | unix.O_NOFOLLOW
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fd, err := unix.Openat(int(dirFd.Fd()), filename, flags, fileMode)
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if err != nil {
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return nil, err
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}
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return os.NewFile(uintptr(fd), root+"/"+subpath), nil
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}
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