extract: Proper modes with multiple copies

We use the source tar entry header to compute fs.FileMode. When the
target path has a different mode, we modify the source header first.
Consequently, when a source path is mapped to multiple target paths, and
when one target path overrides the mode and the following one doesn't,
the following one will have the first one's mode. Fix it by remembering
the source header mode.

internal/deb/extract.go

@@ -245,6 +245,7 @@ func extractData(dataReader io.Reader, options *ExtractOptions) error {
 		}
 
 		var pathReader io.Reader = tarReader
+		origMode := tarHeader.Mode
 		for _, extractInfo := range extractInfos {
 			if contentIsCached {
 				pathReader = bytes.NewReader(contentCache)
@@ -258,6 +259,7 @@ func extractData(dataReader io.Reader, options *ExtractOptions) error {
 			if err := createParents(targetPath); err != nil {
 				return err
 			}
+			tarHeader.Mode = origMode
 			if extractInfo.Mode != 0 {
 				tarHeader.Mode = int64(extractInfo.Mode)
 			}

internal/deb/extract_test.go

@@ -413,6 +413,32 @@ var extractTests = []extractTest{{
 		"/a/b/c/":  "dir 0706",
 		"/a/b/c/d": "file 0601 empty",
 	},
+}, {
+	summary: "Copies with different permissions",
+	pkgdata: testutil.MustMakeDeb([]testutil.TarEntry{
+		DIR(0701, "./a/"),
+		REG(0601, "./b", ""),
+	}),
+	options: deb.ExtractOptions{
+		Extract: map[string][]deb.ExtractInfo{
+			"/a/": []deb.ExtractInfo{
+				{Path: "/b/"},
+				{Path: "/c/", Mode: 0702},
+				{Path: "/d/", Mode: 01777},
+				{Path: "/e/"},
+				{Path: "/f/", Mode: 0723},
+				{Path: "/g/"},
+			},
+		},
+	},
+	result: map[string]string{
+		"/b/": "dir 0701",
+		"/c/": "dir 0702",
+		"/d/": "dir 01777",
+		"/e/": "dir 0701",
+		"/f/": "dir 0723",
+		"/g/": "dir 0701",
+	},
 }}
 
 func (s *S) TestExtract(c *C) {