deb: Fix content file modes to support gdebi, etc.

deb/deb.go

@@ -12,6 +12,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"io/fs"
 	"os"
 	"path/filepath"
 	"strings"
@@ -394,15 +395,21 @@ func createFilesInsideDataTar(info *nfpm.Info, tw *tar.Writer) (md5buf bytes.Buf
 			// skip ghost files in deb
 			continue
 		case files.TypeDir, files.TypeImplicitDir:
-			err = tw.WriteHeader(&tar.Header{
-				Name:     files.AsExplicitRelativePath(file.Destination),
-				Mode:     int64(file.FileInfo.Mode),
-				Typeflag: tar.TypeDir,
-				Format:   tar.FormatGNU,
-				Uname:    file.FileInfo.Owner,
-				Gname:    file.FileInfo.Group,
-				ModTime:  modtime.Get(info.MTime),
-			})
+			header, headerErr := tar.FileInfoHeader(file, "") // headerErr to avoid shadowing err
+			if err != nil {
+				return md5buf, 0, fmt.Errorf("build directory header: %w", headerErr)
+			}
+
+			// we need to change the type from file to dir because
+			// tar.FileInfoHEader thinks it is a file because the file mode does
+			// not contain type flags and in this case, it ignores file.IsDir().
+			header.Typeflag = tar.TypeDir
+			header.Name = files.AsExplicitRelativePath(file.Destination)
+			header.Format = tar.FormatGNU
+			header.ModTime = modtime.Get(info.MTime)
+			header.Mode = addSpecialBits(header.Mode, file.Mode())
+
+			err = tw.WriteHeader(header)
 		case files.TypeSymlink:
 			err = newItemInsideTar(tw, []byte{}, &tar.Header{
 				Name:     files.AsExplicitRelativePath(file.Destination),
@@ -438,13 +445,10 @@ func copyToTarAndDigest(file *files.Content, tw *tar.Writer, md5w io.Writer) (in
 		return 0, err
 	}
 
-	// tar.FileInfoHeader only uses file.Mode().Perm() which masks the mode with
-	// 0o777 which we don't want because we want to be able to set the suid bit.
-	header.Mode = int64(file.Mode())
 	header.Format = tar.FormatGNU
 	header.Name = files.AsExplicitRelativePath(file.Destination)
-	header.Uname = file.FileInfo.Owner
-	header.Gname = file.FileInfo.Group
+	header.Mode = addSpecialBits(header.Mode, file.Mode())
+
 	if err := tw.WriteHeader(header); err != nil {
 		return 0, fmt.Errorf("cannot write header of %s to data.tar.gz: %w", file.Source, err)
 	}
@@ -804,3 +808,23 @@ func writeControl(w io.Writer, data controlData) error {
 	})
 	return template.Must(tmpl.Parse(controlTemplate)).Execute(w, data)
 }
+
+func addSpecialBits(originalMode int64, specialBits fs.FileMode) int64 {
+	const (
+		ISUID = 0o4000 // Set uid
+		ISGID = 0o2000 // Set gid
+		ISVTX = 0o1000 // Save text (sticky bit)
+	)
+
+	if specialBits&fs.ModeSetuid != 0 {
+		originalMode |= ISUID
+	}
+	if specialBits&fs.ModeSetgid != 0 {
+		originalMode |= ISGID
+	}
+	if specialBits&fs.ModeSticky != 0 {
+		originalMode |= ISVTX
+	}
+
+	return originalMode
+}

files/files.go

@@ -66,6 +66,15 @@ type Content struct {
 	Expand      bool             `yaml:"expand,omitempty" json:"expand,omitempty"`
 }
 
+// FileInfoNames is used to make sure *Content satisfies tar.FileInfoNames.
+type FileInfoNames interface {
+	fs.FileInfo
+	Uname() (string, error)
+	Gname() (string, error)
+}
+
+var _ FileInfoNames = &Content{}
+
 type ContentFileInfo struct {
 	Owner string      `yaml:"owner,omitempty" json:"owner,omitempty"`
 	Group string      `yaml:"group,omitempty" json:"group,omitempty"`
@@ -183,7 +192,15 @@ func (c *Content) ModTime() time.Time {
 
 // IsDir to part of the os.FileInfo interface
 func (c *Content) IsDir() bool {
-	return false
+	return c.Type == TypeDir || c.Type == TypeImplicitDir
+}
+
+func (c *Content) Uname() (string, error) {
+	return c.FileInfo.Owner, nil
+}
+
+func (c *Content) Gname() (string, error) {
+	return c.FileInfo.Group, nil
 }
 
 // Sys to part of the os.FileInfo interface