251 lines
8.1 KiB
Go
251 lines
8.1 KiB
Go
//go:build linux
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package safeio
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import (
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"crypto/rand"
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"encoding/hex"
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"io/fs"
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"os"
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"strings"
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"golang.org/x/sys/unix"
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)
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// ReadCanonicalRegular opens an absolute canonical path component by component from the root
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// descriptor. O_NOFOLLOW rejects symlinks at every component, and the open directory descriptors
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// prevent later parent replacement from redirecting the final open.
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func ReadCanonicalRegular(path string, maximum int64) ([]byte, error) {
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if err := ValidateCanonicalPath(path); err != nil {
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return nil, err
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}
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components := strings.Split(strings.TrimPrefix(path, string(os.PathSeparator)), string(os.PathSeparator))
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if len(components) == 0 || components[0] == "" {
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return nil, ErrUnsafeFile
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}
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directory, err := unix.Open(string(os.PathSeparator), unix.O_RDONLY|unix.O_CLOEXEC|unix.O_DIRECTORY, 0)
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if err != nil {
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return nil, ErrUnsafeFile
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}
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directories := []int{directory}
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defer func() { closeUnixDescriptors(directories) }()
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for _, component := range components[:len(components)-1] {
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nextDirectory, err := unix.Openat(directory, component, unix.O_RDONLY|unix.O_CLOEXEC|unix.O_DIRECTORY|unix.O_NOFOLLOW, 0)
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if err != nil {
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return nil, ErrUnsafeFile
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}
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directory = nextDirectory
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directories = append(directories, directory)
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}
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descriptor, err := unix.Openat(directory, components[len(components)-1], unix.O_RDONLY|unix.O_CLOEXEC|unix.O_NOFOLLOW|unix.O_NONBLOCK, 0)
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if err != nil {
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return nil, ErrUnsafeFile
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}
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file := os.NewFile(uintptr(descriptor), "thothctl-safeio")
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if file == nil {
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unix.Close(descriptor)
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return nil, ErrUnsafeFile
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}
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defer file.Close()
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var before, after unix.Stat_t
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if err := unix.Fstat(int(file.Fd()), &before); err != nil || before.Nlink > 1 || before.Mode&unix.S_IFMT != unix.S_IFREG {
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return nil, ErrUnsafeFile
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}
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contents, err := readBoundedRegularFile(file, maximum)
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if err != nil {
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return nil, ErrUnsafeFile
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}
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// Checking the retained descriptor alone misses a pathname replacement while the
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// read is in progress. The parent descriptor and final name must still resolve to
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// the exact open file after reading.
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if err := unix.Fstat(int(file.Fd()), &after); err != nil || after.Nlink > 1 || after.Mode != before.Mode || after.Ino != before.Ino || after.Dev != before.Dev || after.Size != before.Size {
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return nil, ErrUnsafeFile
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}
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var named unix.Stat_t
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if err := unix.Fstatat(directory, components[len(components)-1], &named, unix.AT_SYMLINK_NOFOLLOW); err != nil || named.Nlink > 1 || named.Mode != before.Mode || named.Ino != before.Ino || named.Dev != before.Dev {
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return nil, ErrUnsafeFile
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}
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if !recheckUnixParents(components, directories) {
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return nil, ErrUnsafeFile
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}
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return contents, nil
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}
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func closeUnixDescriptors(descriptors []int) {
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for _, descriptor := range descriptors {
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unix.Close(descriptor)
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}
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}
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func writeCanonicalExclusive(path string, contents []byte, mode fs.FileMode) error {
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if err := ValidateCanonicalPath(path); err != nil || len(contents) > 16<<20 || mode.Perm() != 0o600 {
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return ErrUnsafeFile
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}
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components := strings.Split(strings.TrimPrefix(path, string(os.PathSeparator)), string(os.PathSeparator))
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if len(components) == 0 || components[0] == "" {
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return ErrUnsafeFile
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}
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dir, err := unix.Open("/", unix.O_RDONLY|unix.O_DIRECTORY|unix.O_CLOEXEC, 0)
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if err != nil {
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return ErrUnsafeFile
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}
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defer func() { _ = unix.Close(dir) }()
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for _, component := range components[:len(components)-1] {
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next, openErr := unix.Openat(dir, component, unix.O_RDONLY|unix.O_DIRECTORY|unix.O_CLOEXEC|unix.O_NOFOLLOW, 0)
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if openErr != nil {
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return ErrUnsafeFile
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}
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_ = unix.Close(dir)
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dir = next
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}
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// This is a capability publication API: the retained parent is the namespace
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// anchor. The lexical check is only a pre-commit diagnostic and cannot close an
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// ancestor rename race atomically.
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if !recheckUnixParentPath(components[:len(components)-1], dir) {
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return ErrUnsafeFile
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}
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fd, err := unix.Openat(dir, ".", unix.O_RDWR|unix.O_CLOEXEC|unix.O_TMPFILE, uint32(mode.Perm()))
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if err != nil {
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return ErrUnsafeFile
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}
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file := os.NewFile(uintptr(fd), "thothctl-safeio-anonymous")
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if file == nil {
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_ = unix.Close(fd)
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return ErrUnsafeFile
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}
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closed := false
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closeFile := func() error {
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if closed {
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return nil
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}
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closed = true
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return file.Close()
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}
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fail := func() error {
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_ = closeFile()
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return ErrUnsafeFile
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}
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var expected unix.Stat_t
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if err := unix.Fstat(fd, &expected); err != nil || expected.Nlink != 0 || expected.Mode&unix.S_IFMT != unix.S_IFREG {
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return fail()
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}
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if err := file.Chmod(mode); err != nil {
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return fail()
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}
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if n, err := file.Write(contents); err != nil || n != len(contents) {
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return fail()
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}
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if err := file.Sync(); err != nil {
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return fail()
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}
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var after unix.Stat_t
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if err := unix.Fstat(fd, &after); err != nil || after.Nlink != 0 || after.Mode&unix.S_IFMT != unix.S_IFREG || after.Size != int64(len(contents)) {
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return fail()
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}
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if !recheckUnixParentPath(components[:len(components)-1], dir) {
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return fail()
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}
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// All fallible preparation, checks, and syncs happen before the linearization
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// point. A directory sync here is best effort durability for the retained
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// parent; it cannot be used to report failure after Linkat.
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if err := unix.Fsync(dir); err != nil {
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return fail()
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}
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if !recheckUnixParentPath(components[:len(components)-1], dir) {
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return fail()
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}
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if err := unix.Linkat(fd, "", dir, components[len(components)-1], unix.AT_EMPTY_PATH); err != nil {
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return fail()
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}
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// Linkat is the final commit. Close errors and any post-commit observations
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// are deliberately ignored: returning ErrUnsafeFile here would lie about a
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// candidate that is already committed, and pathname cleanup would be racy.
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_ = closeFile()
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return nil
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}
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func privateStageName() (string, error) {
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var random [16]byte
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if _, err := rand.Read(random[:]); err != nil {
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return "", err
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}
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return ".thothctl-candidate-" + hex.EncodeToString(random[:]), nil
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}
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func validateCanonicalOutputPath(path string) error {
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if err := ValidateCanonicalPath(path); err != nil {
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return err
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}
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components := strings.Split(strings.TrimPrefix(path, string(os.PathSeparator)), string(os.PathSeparator))
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if len(components) < 2 || components[0] == "" {
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return ErrUnsafeFile
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}
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dir, err := unix.Open("/", unix.O_RDONLY|unix.O_DIRECTORY|unix.O_CLOEXEC, 0)
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if err != nil {
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return ErrUnsafeFile
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}
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defer func() { unix.Close(dir) }()
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for _, component := range components[:len(components)-1] {
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next, err := unix.Openat(dir, component, unix.O_RDONLY|unix.O_DIRECTORY|unix.O_CLOEXEC|unix.O_NOFOLLOW, 0)
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if err != nil {
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return ErrUnsafeFile
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}
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unix.Close(dir)
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dir = next
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}
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var st unix.Stat_t
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if err := unix.Fstatat(dir, components[len(components)-1], &st, unix.AT_SYMLINK_NOFOLLOW); err == nil {
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return ErrUnsafeFile
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} else if err != unix.ENOENT {
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return ErrUnsafeFile
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}
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return nil
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}
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func recheckUnixParents(components []string, retained []int) bool {
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if len(retained) != len(components) {
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return false
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}
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dir, err := unix.Open("/", unix.O_RDONLY|unix.O_DIRECTORY|unix.O_CLOEXEC, 0)
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if err != nil {
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return false
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}
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defer func() { unix.Close(dir) }()
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for i, component := range components[:len(components)-1] {
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next, e := unix.Openat(dir, component, unix.O_RDONLY|unix.O_DIRECTORY|unix.O_CLOEXEC|unix.O_NOFOLLOW, 0)
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if e != nil {
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return false
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}
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var got, want unix.Stat_t
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if unix.Fstat(next, &got) != nil || unix.Fstat(retained[i+1], &want) != nil || got.Ino != want.Ino || got.Dev != want.Dev {
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unix.Close(next)
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return false
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}
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unix.Close(dir)
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dir = next
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}
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return true
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}
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func recheckUnixParentPath(components []string, retained int) bool {
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dir, err := unix.Open("/", unix.O_RDONLY|unix.O_DIRECTORY|unix.O_CLOEXEC, 0)
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if err != nil {
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return false
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}
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defer func() { unix.Close(dir) }()
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for _, component := range components {
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next, e := unix.Openat(dir, component, unix.O_RDONLY|unix.O_DIRECTORY|unix.O_CLOEXEC|unix.O_NOFOLLOW, 0)
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if e != nil {
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return false
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}
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unix.Close(dir)
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dir = next
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}
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var got, want unix.Stat_t
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return unix.Fstat(dir, &got) == nil && unix.Fstat(retained, &want) == nil && got.Ino == want.Ino && got.Dev == want.Dev
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}
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func validatePlatformPathSyntax(path string) error { return nil }
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