[release-branch.go1.18] 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 #53710
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/+/417060
Reviewed-by: Tatiana Bradley <tatiana@golang.org>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>

diff --git a/src/encoding/gob/decode.go b/src/encoding/gob/decode.go
index 34f302a5cf54d60e6e5cf9d163d4ad8f6f9c7a6b..eea2924f1ad6274f48fdbe0f5c63bce07a1be41c 100644 (file)
--- a/src/encoding/gob/decode.go
+++ b/src/encoding/gob/decode.go
@@ -871,8 +871,13 @@ func (dec *Decoder) decOpFor(wireId typeId, rt reflect.Type, name string, inProg
        return &op
 }
 
+var maxIgnoreNestingDepth = 10000
+
 // decIgnoreOpFor returns the decoding op for a field that has no destination.
-func (dec *Decoder) decIgnoreOpFor(wireId typeId, inProgress map[typeId]*decOp) *decOp {
+func (dec *Decoder) decIgnoreOpFor(wireId typeId, inProgress map[typeId]*decOp, depth int) *decOp {
+       if depth > maxIgnoreNestingDepth {
+               error_(errors.New("invalid nesting depth"))
+       }
        // If this type is already in progress, it's a recursive type (e.g. map[string]*T).
        // Return the pointer to the op we're already building.
        if opPtr := inProgress[wireId]; opPtr != nil {
@@ -896,7 +901,7 @@ func (dec *Decoder) decIgnoreOpFor(wireId typeId, inProgress map[typeId]*decOp)
                        errorf("bad data: undefined type %s", wireId.string())
                case wire.ArrayT != nil:
                        elemId := wire.ArrayT.Elem
-                       elemOp := dec.decIgnoreOpFor(elemId, inProgress)
+                       elemOp := dec.decIgnoreOpFor(elemId, inProgress, depth+1)
                        op = func(i *decInstr, state *decoderState, value reflect.Value) {
                                state.dec.ignoreArray(state, *elemOp, wire.ArrayT.Len)
                        }
@@ -904,15 +909,15 @@ func (dec *Decoder) decIgnoreOpFor(wireId typeId, inProgress map[typeId]*decOp)
                case wire.MapT != nil:
                        keyId := dec.wireType[wireId].MapT.Key
                        elemId := dec.wireType[wireId].MapT.Elem
-                       keyOp := dec.decIgnoreOpFor(keyId, inProgress)
-                       elemOp := dec.decIgnoreOpFor(elemId, inProgress)
+                       keyOp := dec.decIgnoreOpFor(keyId, inProgress, depth+1)
+                       elemOp := dec.decIgnoreOpFor(elemId, inProgress, depth+1)
                        op = func(i *decInstr, state *decoderState, value reflect.Value) {
                                state.dec.ignoreMap(state, *keyOp, *elemOp)
                        }
 
                case wire.SliceT != nil:
                        elemId := wire.SliceT.Elem
-                       elemOp := dec.decIgnoreOpFor(elemId, inProgress)
+                       elemOp := dec.decIgnoreOpFor(elemId, inProgress, depth+1)
                        op = func(i *decInstr, state *decoderState, value reflect.Value) {
                                state.dec.ignoreSlice(state, *elemOp)
                        }
@@ -1073,7 +1078,7 @@ func (dec *Decoder) compileSingle(remoteId typeId, ut *userTypeInfo) (engine *de
 func (dec *Decoder) compileIgnoreSingle(remoteId typeId) *decEngine {
        engine := new(decEngine)
        engine.instr = make([]decInstr, 1) // one item
-       op := dec.decIgnoreOpFor(remoteId, make(map[typeId]*decOp))
+       op := dec.decIgnoreOpFor(remoteId, make(map[typeId]*decOp), 0)
        ovfl := overflow(dec.typeString(remoteId))
        engine.instr[0] = decInstr{*op, 0, nil, ovfl}
        engine.numInstr = 1
@@ -1118,7 +1123,7 @@ func (dec *Decoder) compileDec(remoteId typeId, ut *userTypeInfo) (engine *decEn
                localField, present := srt.FieldByName(wireField.Name)
                // TODO(r): anonymous names
                if !present || !isExported(wireField.Name) {
-                       op := dec.decIgnoreOpFor(wireField.Id, make(map[typeId]*decOp))
+                       op := dec.decIgnoreOpFor(wireField.Id, make(map[typeId]*decOp), 0)
                        engine.instr[fieldnum] = decInstr{*op, fieldnum, nil, ovfl}
                        continue
                }

diff --git a/src/encoding/gob/gobencdec_test.go b/src/encoding/gob/gobencdec_test.go
index 1d5dde22a4eeb50b490b04272a476e11d6d46371..3d49887c016767805c704a398c37b86fd5520b0c 100644 (file)
--- 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)
+       }
+}