pkg/rpcserver: pkg/flatrpc: executor: add handshake stage 0

As we figured out in #5805, syz-manager treats random incoming RPC
connections as trusted, and will crash if a non-executor client sends
an invalid packet to it.

To address this issue, we introduce another stage of handshake, which
includes a cookie exchange:
 - upon connection from an executor, the manager sends a ConnectHello RPC
   message to it, which contains a random 64-bit cookie;
 - the executor calculates a hash of that cookie and includes it into
   its ConnectRequest together with the other information;
 - before checking the validity of ConnectRequest, the manager ensures
   client sanity (passed ID didn't change, hashed cookie has the expected
   value)

We deliberately pick a random cookie instead of a magic number: if the
fuzzer somehow learns to send packets to the manager, we don't want it to
crash multiple managers on the same machine.

1 files changed, 103 insertions, 10 deletions

diff --git a/pkg/flatrpc/flatrpc.go b/pkg/flatrpc/flatrpc.go
index fd5b4f614..d04d5c531 100644
--- a/pkg/flatrpc/flatrpc.go
+++ b/pkg/flatrpc/flatrpc.go
@@ -485,7 +485,83 @@ func (v SnapshotState) String() string {
 	return "SnapshotState(" + strconv.FormatInt(int64(v), 10) + ")"
 }
 
+type ConnectHelloRawT struct {
+	Cookie uint64 `json:"cookie"`
+}
+
+func (t *ConnectHelloRawT) Pack(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
+	if t == nil {
+		return 0
+	}
+	ConnectHelloRawStart(builder)
+	ConnectHelloRawAddCookie(builder, t.Cookie)
+	return ConnectHelloRawEnd(builder)
+}
+
+func (rcv *ConnectHelloRaw) UnPackTo(t *ConnectHelloRawT) {
+	t.Cookie = rcv.Cookie()
+}
+
+func (rcv *ConnectHelloRaw) UnPack() *ConnectHelloRawT {
+	if rcv == nil {
+		return nil
+	}
+	t := &ConnectHelloRawT{}
+	rcv.UnPackTo(t)
+	return t
+}
+
+type ConnectHelloRaw struct {
+	_tab flatbuffers.Table
+}
+
+func GetRootAsConnectHelloRaw(buf []byte, offset flatbuffers.UOffsetT) *ConnectHelloRaw {
+	n := flatbuffers.GetUOffsetT(buf[offset:])
+	x := &ConnectHelloRaw{}
+	x.Init(buf, n+offset)
+	return x
+}
+
+func GetSizePrefixedRootAsConnectHelloRaw(buf []byte, offset flatbuffers.UOffsetT) *ConnectHelloRaw {
+	n := flatbuffers.GetUOffsetT(buf[offset+flatbuffers.SizeUint32:])
+	x := &ConnectHelloRaw{}
+	x.Init(buf, n+offset+flatbuffers.SizeUint32)
+	return x
+}
+
+func (rcv *ConnectHelloRaw) Init(buf []byte, i flatbuffers.UOffsetT) {
+	rcv._tab.Bytes = buf
+	rcv._tab.Pos = i
+}
+
+func (rcv *ConnectHelloRaw) Table() flatbuffers.Table {
+	return rcv._tab
+}
+
+func (rcv *ConnectHelloRaw) Cookie() uint64 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
+	if o != 0 {
+		return rcv._tab.GetUint64(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *ConnectHelloRaw) MutateCookie(n uint64) bool {
+	return rcv._tab.MutateUint64Slot(4, n)
+}
+
+func ConnectHelloRawStart(builder *flatbuffers.Builder) {
+	builder.StartObject(1)
+}
+func ConnectHelloRawAddCookie(builder *flatbuffers.Builder, cookie uint64) {
+	builder.PrependUint64Slot(0, cookie, 0)
+}
+func ConnectHelloRawEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
+	return builder.EndObject()
+}
+
 type ConnectRequestRawT struct {
+	Cookie      uint64 `json:"cookie"`
 	Id          int64  `json:"id"`
 	Arch        string `json:"arch"`
 	GitRevision string `json:"git_revision"`
@@ -500,6 +576,7 @@ func (t *ConnectRequestRawT) Pack(builder *flatbuffers.Builder) flatbuffers.UOff
 	gitRevisionOffset := builder.CreateString(t.GitRevision)
 	syzRevisionOffset := builder.CreateString(t.SyzRevision)
 	ConnectRequestRawStart(builder)
+	ConnectRequestRawAddCookie(builder, t.Cookie)
 	ConnectRequestRawAddId(builder, t.Id)
 	ConnectRequestRawAddArch(builder, archOffset)
 	ConnectRequestRawAddGitRevision(builder, gitRevisionOffset)
@@ -508,6 +585,7 @@ func (t *ConnectRequestRawT) Pack(builder *flatbuffers.Builder) flatbuffers.UOff
 }
 
 func (rcv *ConnectRequestRaw) UnPackTo(t *ConnectRequestRawT) {
+	t.Cookie = rcv.Cookie()
 	t.Id = rcv.Id()
 	t.Arch = string(rcv.Arch())
 	t.GitRevision = string(rcv.GitRevision())
@@ -550,20 +628,32 @@ func (rcv *ConnectRequestRaw) Table() flatbuffers.Table {
 	return rcv._tab
 }
 
-func (rcv *ConnectRequestRaw) Id() int64 {
+func (rcv *ConnectRequestRaw) Cookie() uint64 {
 	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
 	if o != 0 {
+		return rcv._tab.GetUint64(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *ConnectRequestRaw) MutateCookie(n uint64) bool {
+	return rcv._tab.MutateUint64Slot(4, n)
+}
+
+func (rcv *ConnectRequestRaw) Id() int64 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
+	if o != 0 {
 		return rcv._tab.GetInt64(o + rcv._tab.Pos)
 	}
 	return 0
 }
 
 func (rcv *ConnectRequestRaw) MutateId(n int64) bool {
-	return rcv._tab.MutateInt64Slot(4, n)
+	return rcv._tab.MutateInt64Slot(6, n)
 }
 
 func (rcv *ConnectRequestRaw) Arch() []byte {
-	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(8))
 	if o != 0 {
 		return rcv._tab.ByteVector(o + rcv._tab.Pos)
 	}
@@ -571,7 +661,7 @@ func (rcv *ConnectRequestRaw) Arch() []byte {
 }
 
 func (rcv *ConnectRequestRaw) GitRevision() []byte {
-	o := flatbuffers.UOffsetT(rcv._tab.Offset(8))
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(10))
 	if o != 0 {
 		return rcv._tab.ByteVector(o + rcv._tab.Pos)
 	}
@@ -579,7 +669,7 @@ func (rcv *ConnectRequestRaw) GitRevision() []byte {
 }
 
 func (rcv *ConnectRequestRaw) SyzRevision() []byte {
-	o := flatbuffers.UOffsetT(rcv._tab.Offset(10))
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(12))
 	if o != 0 {
 		return rcv._tab.ByteVector(o + rcv._tab.Pos)
 	}
@@ -587,19 +677,22 @@ func (rcv *ConnectRequestRaw) SyzRevision() []byte {
 }
 
 func ConnectRequestRawStart(builder *flatbuffers.Builder) {
-	builder.StartObject(4)
+	builder.StartObject(5)
+}
+func ConnectRequestRawAddCookie(builder *flatbuffers.Builder, cookie uint64) {
+	builder.PrependUint64Slot(0, cookie, 0)
 }
 func ConnectRequestRawAddId(builder *flatbuffers.Builder, id int64) {
-	builder.PrependInt64Slot(0, id, 0)
+	builder.PrependInt64Slot(1, id, 0)
 }
 func ConnectRequestRawAddArch(builder *flatbuffers.Builder, arch flatbuffers.UOffsetT) {
-	builder.PrependUOffsetTSlot(1, flatbuffers.UOffsetT(arch), 0)
+	builder.PrependUOffsetTSlot(2, flatbuffers.UOffsetT(arch), 0)
 }
 func ConnectRequestRawAddGitRevision(builder *flatbuffers.Builder, gitRevision flatbuffers.UOffsetT) {
-	builder.PrependUOffsetTSlot(2, flatbuffers.UOffsetT(gitRevision), 0)
+	builder.PrependUOffsetTSlot(3, flatbuffers.UOffsetT(gitRevision), 0)
 }
 func ConnectRequestRawAddSyzRevision(builder *flatbuffers.Builder, syzRevision flatbuffers.UOffsetT) {
-	builder.PrependUOffsetTSlot(3, flatbuffers.UOffsetT(syzRevision), 0)
+	builder.PrependUOffsetTSlot(4, flatbuffers.UOffsetT(syzRevision), 0)
 }
 func ConnectRequestRawEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
 	return builder.EndObject()