fix(unpack): support unpacking readonly folders

layer unpacking preserves the original filemode. If the layer contains
a readonly director, this would cause unpack to fail, because the dir
on disk would not be writeable, and it's children would fail to write.

this change makes all unpacked files owner-writable, which has some
implications for how unpacked files should be used, but for purposes
within opm this will not be an issue.

Author: ecordell

pkg/image/containerdregistry/registry.go

@@ -6,6 +6,10 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+
 	"github.com/containerd/containerd/archive"
 	"github.com/containerd/containerd/archive/compression"
 	"github.com/containerd/containerd/errdefs"
@@ -15,9 +19,6 @@ import (
 	"github.com/containerd/containerd/remotes"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/sirupsen/logrus"
-	"io"
-	"io/ioutil"
-	"os"
 
 	"github.com/operator-framework/operator-registry/pkg/image"
 )
@@ -195,5 +196,11 @@ func adjustPerms(h *tar.Header) (bool, error) {
 	h.Uid = os.Getuid()
 	h.Gid = os.Getgid()
 
+	// Make all unpacked files owner-writable
+	// This prevents errors when unpacking a layer that contains a read-only folder (if permissions are preserved,
+	// file contents cannot be unpacked into the unpacked read-only folder).
+	// This also means that "unpacked" layers cannot be "repacked" without potential information loss
+	h.Mode |= 0200
+
 	return true, nil
 }