archive/tar, archive/zip: disable insecure file name checks with GODEBUG

Add GODEBUG=tarinsecurepath=1 and GODEBUG=zipinsecurepath=1 settings
to disable file name validation.

For #55356.

Change-Id: Iaacdc629189493e7ea3537a81660215a59dd40a4
Reviewed-on: https://go-review.googlesource.com/c/go/+/452495
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Damien Neil <dneil@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>

3 files changed, 24 insertions, 1 deletions

diff --git a/src/archive/tar/common.go b/src/archive/tar/common.go
index be02a24542..0d5a942024 100644
--- a/src/archive/tar/common.go
+++ b/src/archive/tar/common.go
@@ -13,6 +13,7 @@ package tar
 import (
 	"errors"
 	"fmt"
+	"internal/godebug"
 	"io/fs"
 	"math"
 	"path"
@@ -26,6 +27,8 @@ import (
 // architectures. If a large value is encountered when decoding, the result
 // stored in Header will be the truncated version.
 
+var tarinsecurepath = godebug.New("tarinsecurepath")
+
 var (
 	ErrHeader          = errors.New("archive/tar: invalid tar header")
 	ErrWriteTooLong    = errors.New("archive/tar: write too long")
diff --git a/src/archive/tar/reader.go b/src/archive/tar/reader.go
index 3495f083e3..99ba004c9a 100644
--- a/src/archive/tar/reader.go
+++ b/src/archive/tar/reader.go
@@ -60,7 +60,7 @@ func (tr *Reader) Next() (*Header, error) {
 	}
 	hdr, err := tr.next()
 	tr.err = err
-	if err == nil && !filepath.IsLocal(hdr.Name) {
+	if err == nil && tarinsecurepath.Value() != "1" && !filepath.IsLocal(hdr.Name) {
 		err = ErrInsecurePath
 	}
 	return hdr, err
diff --git a/src/archive/tar/reader_test.go b/src/archive/tar/reader_test.go
index 91dc1650e2..7e0462c3f8 100644
--- a/src/archive/tar/reader_test.go
+++ b/src/archive/tar/reader_test.go
@@ -1617,6 +1617,7 @@ func TestFileReader(t *testing.T) {
 }
 
 func TestInsecurePaths(t *testing.T) {
+	t.Setenv("GODEBUG", "tarinsecurepath=0")
 	for _, path := range []string{
 		"../foo",
 		"/foo",
@@ -1652,3 +1653,22 @@ func TestInsecurePaths(t *testing.T) {
 		}
 	}
 }
+
+func TestDisableInsecurePathCheck(t *testing.T) {
+	t.Setenv("GODEBUG", "tarinsecurepath=1")
+	var buf bytes.Buffer
+	tw := NewWriter(&buf)
+	const name = "/foo"
+	tw.WriteHeader(&Header{
+		Name: name,
+	})
+	tw.Close()
+	tr := NewReader(&buf)
+	h, err := tr.Next()
+	if err != nil {
+		t.Fatalf("tr.Next with tarinsecurepath=1: got err %v, want nil", err)
+	}
+	if h.Name != name {
+		t.Fatalf("tr.Next with tarinsecurepath=1: got name %q, want %q", h.Name, name)
+	}
+}