[release-branch.go1.17] encoding/gob: add a depth limit for ignored fields

Enforce a nesting limit of 10,000 for ignored fields during decoding
of messages. This prevents the possibility of triggering stack
exhaustion.

Fixes #53709
Updates #53615
Fixes CVE-2022-30635

Change-Id: I05103d06dd5ca3945fcba3c1f5d3b5a645e8fb0f
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1484771
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Tatiana Bradley <tatianabradley@google.com>
(cherry picked from commit 55e8f938d22bfec29cc9dc9671044c5a41d1ea9c)
Reviewed-on: https://go-review.googlesource.com/c/go/+/417074
Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/src/encoding/gob/gobencdec_test.go b/src/encoding/gob/gobencdec_test.go
index 6d2c8db42d..1b52ecc6c8 100644
--- a/src/encoding/gob/gobencdec_test.go
+++ b/src/encoding/gob/gobencdec_test.go
@@ -12,6 +12,7 @@ import (
 	"fmt"
 	"io"
 	"net"
+	"reflect"
 	"strings"
 	"testing"
 	"time"
@@ -796,3 +797,26 @@ func TestNetIP(t *testing.T) {
 		t.Errorf("decoded to %v, want 1.2.3.4", ip.String())
 	}
 }
+
+func TestIngoreDepthLimit(t *testing.T) {
+	// We don't test the actual depth limit because it requires building an
+	// extremely large message, which takes quite a while.
+	oldNestingDepth := maxIgnoreNestingDepth
+	maxIgnoreNestingDepth = 100
+	defer func() { maxIgnoreNestingDepth = oldNestingDepth }()
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	typ := reflect.TypeOf(int(0))
+	nested := reflect.ArrayOf(1, typ)
+	for i := 0; i < 100; i++ {
+		nested = reflect.ArrayOf(1, nested)
+	}
+	badStruct := reflect.New(reflect.StructOf([]reflect.StructField{{Name: "F", Type: nested}}))
+	enc.Encode(badStruct.Interface())
+	dec := NewDecoder(b)
+	var output struct{ Hello int }
+	expectedErr := "invalid nesting depth"
+	if err := dec.Decode(&output); err == nil || err.Error() != expectedErr {
+		t.Errorf("Decode didn't fail with depth limit of 100: want %q, got %q", expectedErr, err)
+	}
+}