encoding/xml: use iterative Skip, rather than recursive

Prevents exhausting the stack limit in _incredibly_ deeply nested
structures.

Fixes #53614
Fixes CVE-2022-28131

Change-Id: I47db4595ce10cecc29fbd06afce7b299868599e6
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1419912
Reviewed-by: Julie Qiu <julieqiu@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/417062
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

diff --git a/src/encoding/xml/read.go b/src/encoding/xml/read.go
index 01613065e3103e856988e72c719123b46af492ab..a6fb6654585c645a90457656e58625d90a879834 100644 (file)
--- a/src/encoding/xml/read.go
+++ b/src/encoding/xml/read.go
@@ -747,12 +747,12 @@ Loop:
 }
 
 // Skip reads tokens until it has consumed the end element
-// matching the most recent start element already consumed.
-// It recurs if it encounters a start element, so it can be used to
-// skip nested structures.
+// matching the most recent start element already consumed,
+// skipping nested structures.
 // It returns nil if it finds an end element matching the start
 // element; otherwise it returns an error describing the problem.
 func (d *Decoder) Skip() error {
+       var depth int64
        for {
                tok, err := d.Token()
                if err != nil {
@@ -760,11 +760,12 @@ func (d *Decoder) Skip() error {
                }
                switch tok.(type) {
                case StartElement:
-                       if err := d.Skip(); err != nil {
-                               return err
-                       }
+                       depth++
                case EndElement:
-                       return nil
+                       if depth == 0 {
+                               return nil
+                       }
+                       depth--
                }
        }
 }

diff --git a/src/encoding/xml/read_test.go b/src/encoding/xml/read_test.go
index 42059db3ae6ede5cab17e23b9070d9b7cc301b03..58d1eddb6123f054eeb6fead8f30e1720df72f53 100644 (file)
--- a/src/encoding/xml/read_test.go
+++ b/src/encoding/xml/read_test.go
@@ -9,6 +9,7 @@ import (
        "errors"
        "io"
        "reflect"
+       "runtime"
        "strings"
        "testing"
        "time"
@@ -1109,3 +1110,19 @@ func TestCVE202228131(t *testing.T) {
                t.Fatalf("Unmarshal unexpected error: got %q, want %q", err, errExeceededMaxUnmarshalDepth)
        }
 }
+
+func TestCVE202230633(t *testing.T) {
+       if runtime.GOARCH == "wasm" {
+               t.Skip("causes memory exhaustion on js/wasm")
+       }
+       defer func() {
+               p := recover()
+               if p != nil {
+                       t.Fatal("Unmarshal panicked")
+               }
+       }()
+       var example struct {
+               Things []string
+       }
+       Unmarshal(bytes.Repeat([]byte("<a>"), 17_000_000), &example)
+}