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chunked: fix another occurrence of linkat #1052

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Nov 3, 2021
Merged

chunked: fix another occurrence of linkat #1052

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35 changes: 20 additions & 15 deletions pkg/chunked/storage_linux.go
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Original file line number Diff line number Diff line change
Expand Up @@ -67,6 +67,24 @@ func timeToTimespec(time time.Time) (ts unix.Timespec) {
return unix.NsecToTimespec(time.UnixNano())
}

func doHardLink(srcFd int, destDirFd int, destBase string) error {
doLink := func() error {
// Using unix.AT_EMPTY_PATH requires CAP_DAC_READ_SEARCH while this variant that uses
// /proc/self/fd doesn't and can be used with rootless.
srcPath := fmt.Sprintf("/proc/self/fd/%d", srcFd)
return unix.Linkat(unix.AT_FDCWD, srcPath, destDirFd, destBase, unix.AT_SYMLINK_FOLLOW)
}

err := doLink()

// if the destination exists, unlink it first and try again
if err != nil && os.IsExist(err) {
unix.Unlinkat(destDirFd, destBase, 0)
return doLink()
}
return err
}

func copyFileContent(srcFd int, destFile string, dirfd int, mode os.FileMode, useHardLinks bool) (*os.File, int64, error) {
src := fmt.Sprintf("/proc/self/fd/%d", srcFd)
st, err := os.Stat(src)
Expand All @@ -83,20 +101,7 @@ func copyFileContent(srcFd int, destFile string, dirfd int, mode os.FileMode, us
if err == nil {
defer destDir.Close()

doLink := func() error {
// Using unix.AT_EMPTY_PATH requires CAP_DAC_READ_SEARCH while this variant that uses
// /proc/self/fd doesn't and can be used with rootless.
srcPath := fmt.Sprintf("/proc/self/fd/%d", srcFd)
return unix.Linkat(unix.AT_FDCWD, srcPath, int(destDir.Fd()), destBase, unix.AT_SYMLINK_FOLLOW)
}

err := doLink()

// if the destination exists, unlink it first and try again
if err != nil && os.IsExist(err) {
unix.Unlinkat(int(destDir.Fd()), destBase, 0)
err = doLink()
}
err := doHardLink(srcFd, int(destDir.Fd()), destBase)
if err == nil {
return nil, st.Size(), nil
}
Expand Down Expand Up @@ -797,7 +802,7 @@ func safeLink(dirfd int, mode os.FileMode, metadata *internal.FileMetadata, opti
destDirFd = int(f.Fd())
}

err = unix.Linkat(int(sourceFile.Fd()), "", destDirFd, destBase, unix.AT_EMPTY_PATH)
err = doHardLink(int(sourceFile.Fd()), destDirFd, destBase)
if err != nil {
return err
}
Expand Down