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, 1 insertions, 0 deletions

diff --git a/pkg/flatrpc/helpers.go b/pkg/flatrpc/helpers.go
index 9a5463b24..5aa5cfe74 100644
--- a/pkg/flatrpc/helpers.go
+++ b/pkg/flatrpc/helpers.go
@@ -18,6 +18,7 @@ const AllFeatures = ^Feature(0)
 // Flatbuffers compiler adds T suffix to object API types, which are actual structs representing types.
 // This leads to non-idiomatic Go code, e.g. we would have to use []FileInfoT in Go code.
 // So we use Raw suffix for all flatbuffers tables and rename object API types here to idiomatic names.
+type ConnectHello = ConnectHelloRawT
 type ConnectRequest = ConnectRequestRawT
 type ConnectReply = ConnectReplyRawT
 type InfoRequest = InfoRequestRawT