From dcb84828a6b1d7d4d9186bc6d752cc147e255162 Mon Sep 17 00:00:00 2001 From: LE Manh Cuong Date: Mon, 29 Apr 2019 22:57:25 +0700 Subject: [PATCH] encoding/json: fix Unmarshal hang on recursive pointers MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit indirect walks down v until it gets to a non-pointer. But it does not handle the case when v is a pointer to itself, like in: var v interface{} v = &v Unmarshal(b, v) So just stop immediately if we see v is a pointer to itself. Fixes #31740 Change-Id: Ie396264119e24d70284cd9bf76dcb2050babb069 Reviewed-on: https://go-review.googlesource.com/c/go/+/174337 Run-TryBot: Daniel Martí TryBot-Result: Gobot Gobot Reviewed-by: Daniel Martí Reviewed-by: Brad Fitzpatrick --- src/encoding/json/decode.go | 8 ++++++++ src/encoding/json/decode_test.go | 12 ++++++++++++ 2 files changed, 20 insertions(+) diff --git a/src/encoding/json/decode.go b/src/encoding/json/decode.go index 3ca3d7803e..bdd94e34ce 100644 --- a/src/encoding/json/decode.go +++ b/src/encoding/json/decode.go @@ -535,6 +535,14 @@ func indirect(v reflect.Value, decodingNull bool) (Unmarshaler, encoding.TextUnm if v.Elem().Kind() != reflect.Ptr && decodingNull && v.CanSet() { break } + + // Prevent infinite loop if v is an interface pointing to its own address: + // var v interface{} + // v = &v + if v.Elem().Kind() == reflect.Interface && v.Elem().Elem() == v { + v = v.Elem() + break + } if v.IsNil() { v.Set(reflect.New(v.Type().Elem())) } diff --git a/src/encoding/json/decode_test.go b/src/encoding/json/decode_test.go index 8da74fa3d3..719a9fa290 100644 --- a/src/encoding/json/decode_test.go +++ b/src/encoding/json/decode_test.go @@ -2334,3 +2334,15 @@ func TestUnmarshalPanic(t *testing.T) { Unmarshal([]byte("{}"), &unmarshalPanic{}) t.Fatalf("Unmarshal should have panicked") } + +// The decoder used to hang if decoding into an interface pointing to its own address. +// See golang.org/issues/31740. +func TestUnmarshalRecursivePointer(t *testing.T) { + var v interface{} + v = &v + data := []byte(`{"a": "b"}`) + + if err := Unmarshal(data, v); err != nil { + t.Fatal(err) + } +} -- 2.50.0