nil pointer deference in proto.Size

[jpbetz]

When adding a proto.Size() call to code in etcd, we encountered this error:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0xa90726]

github.com/coreos/etcd/etcdserver/etcdserverpb.(*PutResponse).Size(0x0, 0x4cac5b)
        /usr/local/google/home/jpbetz/Projects/etcd/src/github.com/coreos/etcd/etcdserver/etcdserverpb/rpc.pb.go:8148 +0x26
github.com/coreos/etcd/etcdserver/etcdserverpb.(*PutResponse).Marshal(0x0, 0x176af60, 0x0, 0x7fbfb4a53af0, 0x0, 0x1)
        /usr/local/google/home/jpbetz/Projects/etcd/src/github.com/coreos/etcd/etcdserver/etcdserverpb/rpc.pb.go:5161 +0x2f
github.com/coreos/etcd/vendor/github.com/golang/protobuf/proto.Size(0x176af60, 0x0, 0xc420117880)
        /usr/local/google/home/jpbetz/Projects/etcd/src/github.com/coreos/etcd/vendor/github.com/golang/protobuf/proto/table_marshal.go:2602 +0x100
github.com/coreos/etcd/etcdserver.warnOfExpensiveRequest(0xc428750060, 0xbebecd857a50c3e6, 0xdde501b3a, 0x17c4620, 0x17604e0, 0xc4203a88c0, 0x176af60, 0x0, 0x175f920, 0xc42014db10)

Here the nil pointer dereference appears to occur here:

https://github.com/coreos/etcd/blob/c6e18c712c7cc336a86404478297afa6063a72eb/etcdserver/etcdserverpb/rpc.pb.go#L8148

The nil was propagated here:

https://github.com/coreos/etcd/blob/c6e18c712c7cc336a86404478297afa6063a72eb/etcdserver/etcdserverpb/rpc.pb.go#L5161

And appears to have originated here:

protobuf/proto/table_marshal.go

Line 2602 in b4deda0

b, _ := m.Marshal()

Suggesting that a nil check needs to be added to f m, ok := pb.(Marshaler); ok { ?

Versions:

github.com/golang/protobuf v1.1.0
github.com/gogo/protobuf v1.0.0

[gyuho]

To reproduce:

package main

import (
	"fmt"

	"github.com/coreos/etcd/etcdserver/etcdserverpb"
	"github.com/golang/protobuf/proto"
)

func main() {
	var msg *etcdserverpb.PutResponse
	m := proto.Message(msg)
	a, b := m.(proto.Marshaler)
	fmt.Println(a, b) // <nil> true

	// trigger panic
	a.Marshal()
	/*
	   panic: runtime error: invalid memory address or nil pointer dereference
	   [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x7e2826]

	   goroutine 1 [running]:
	   github.com/coreos/etcd/etcdserver/etcdserverpb.(*PutResponse).Size(0x0, 0x9cbe00)
	   	/home/gyuho/go/src/github.com/coreos/etcd/etcdserver/etcdserverpb/rpc.pb.go:8148 +0x26
	   github.com/coreos/etcd/etcdserver/etcdserverpb.(*PutResponse).Marshal(0x0, 0x2, 0x2, 0xb, 0x0, 0x0)
	   	/home/gyuho/go/src/github.com/coreos/etcd/etcdserver/etcdserverpb/rpc.pb.go:5161 +0x2f
	   main.main()
	   	/home/gyuho/p.go:15 +0xce
	   exit status 2
	*/
}

[jpbetz]

Turns out that the input to proto.Size was a non-nil interface with a nil value pointer. By checking for both msg != nil && !reflect.ValueOf(msg).IsNil() before calling proto.Size we were able to resolve the issue.