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os: RemoveAll: fix symlink race for unix
Since all the platforms now support O_DIRECTORY flag for open, it can be used to (together with O_NOFOLLOW) to ensure we open a directory, thus eliminating the need to call stat before open. This fixes the symlink race, when a directory is replaced by a symlink in between stat and open calls. While at it, rename openFdAt to openDirAt, because this function is (and was) meant for directories only. NOTE Solaris supports O_DIRECTORY since before Solaris 11 (which is the only version Go supports since supported version now), and Illumos always had it. The only missing piece was O_DIRECTORY flag value, which is taken from golang.org/x/sys/unix. Updates #52745. Change-Id: Ic1111d688eebc8804a87d39d3261c2a6eb33f176 Reviewed-on: https://go-review.googlesource.com/c/go/+/588495 Reviewed-by: Ian Lance Taylor <iant@google.com> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Aleksa Sarai <cyphar@cyphar.com> Reviewed-by: Than McIntosh <thanm@google.com> Auto-Submit: Ian Lance Taylor <iant@google.com>
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@ -152,7 +152,7 @@ const (
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kindSock
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// kindNoPoll means that we should not put the descriptor into
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// non-blocking mode, because we know it is not a pipe or FIFO.
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// Used by openFdAt and openDirNolog for directories.
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// Used by openDirAt and openDirNolog for directories.
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kindNoPoll
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)
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@ -260,7 +260,7 @@ func epipecheck(file *File, e error) {
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const DevNull = "/dev/null"
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// openFileNolog is the Unix implementation of OpenFile.
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// Changes here should be reflected in openFdAt and openDirNolog, if relevant.
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// Changes here should be reflected in openDirAt and openDirNolog, if relevant.
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func openFileNolog(name string, flag int, perm FileMode) (*File, error) {
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setSticky := false
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if !supportsCreateWithStickyBit && flag&O_CREATE != 0 && perm&ModeSticky != 0 {
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@ -74,22 +74,7 @@ func removeAllFrom(parent *File, base string) error {
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if err != syscall.EISDIR && err != syscall.EPERM && err != syscall.EACCES {
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return &PathError{Op: "unlinkat", Path: base, Err: err}
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}
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// Is this a directory we need to recurse into?
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var statInfo syscall.Stat_t
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statErr := ignoringEINTR(func() error {
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return unix.Fstatat(parentFd, base, &statInfo, unix.AT_SYMLINK_NOFOLLOW)
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})
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if statErr != nil {
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if IsNotExist(statErr) {
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return nil
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}
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return &PathError{Op: "fstatat", Path: base, Err: statErr}
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}
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if statInfo.Mode&syscall.S_IFMT != syscall.S_IFDIR {
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// Not a directory; return the error from the unix.Unlinkat.
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return &PathError{Op: "unlinkat", Path: base, Err: err}
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}
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uErr := err
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// Remove the directory's entries.
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var recurseErr error
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@ -98,11 +83,15 @@ func removeAllFrom(parent *File, base string) error {
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var respSize int
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// Open the directory to recurse into
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file, err := openFdAt(parentFd, base)
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file, err := openDirAt(parentFd, base)
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if err != nil {
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if IsNotExist(err) {
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return nil
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}
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if err == syscall.ENOTDIR {
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// Not a directory; return the error from the unix.Unlinkat.
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return &PathError{Op: "unlinkat", Path: base, Err: uErr}
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}
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recurseErr = &PathError{Op: "openfdat", Path: base, Err: err}
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break
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}
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@ -168,16 +157,19 @@ func removeAllFrom(parent *File, base string) error {
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return &PathError{Op: "unlinkat", Path: base, Err: unlinkError}
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}
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// openFdAt opens path relative to the directory in fd.
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// Other than that this should act like openFileNolog.
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// openDirAt opens a directory name relative to the directory referred to by
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// the file descriptor dirfd. If name is anything but a directory (this
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// includes a symlink to one), it should return an error. Other than that this
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// should act like openFileNolog.
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//
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// This acts like openFileNolog rather than OpenFile because
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// we are going to (try to) remove the file.
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// The contents of this file are not relevant for test caching.
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func openFdAt(dirfd int, name string) (*File, error) {
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func openDirAt(dirfd int, name string) (*File, error) {
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var r int
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for {
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var e error
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r, e = unix.Openat(dirfd, name, O_RDONLY|syscall.O_CLOEXEC, 0)
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r, e = unix.Openat(dirfd, name, O_RDONLY|syscall.O_CLOEXEC|syscall.O_DIRECTORY|syscall.O_NOFOLLOW, 0)
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if e == nil {
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break
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}
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@ -634,6 +634,7 @@ const (
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O_APPEND = 0x8
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O_CLOEXEC = 0x800000
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O_CREAT = 0x100
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O_DIRECTORY = 0x1000000
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O_DSYNC = 0x40
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O_EXCL = 0x400
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O_EXEC = 0x400000
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