From ae82f2b279d2a9e10a9697461b62e5cea0d3cb52 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Gr=C3=A9goire=20Henry?= <gregoire.henry@tezos.com>
Date: Tue, 5 Dec 2017 15:19:25 +0100
Subject: [PATCH] Shell: enforce the context hash of the block header

---
 lib_node_shell/block_validator.ml |  4 ++--
 lib_node_shell/state.ml           | 21 ++++++++++++++++++++-
 lib_node_shell/state.mli          |  2 ++
 3 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/lib_node_shell/block_validator.ml b/lib_node_shell/block_validator.ml
index 0c9a5f53e..6b21a97fe 100644
--- a/lib_node_shell/block_validator.ml
+++ b/lib_node_shell/block_validator.ml
@@ -486,8 +486,6 @@ let rec worker_loop bv =
                   end
                 end >>= function
                 | Ok result -> begin
-                    lwt_log_info "validated block %a"
-                      Block_hash.pp_short hash >>= fun () ->
                     Lwt_utils.protect ~canceler:bv.canceler begin fun () ->
                       Distributed_db.commit_block
                         net_db hash header operations result
@@ -495,6 +493,8 @@ let rec worker_loop bv =
                     | None ->
                         assert false (* should not happen *)
                     | Some block ->
+                        lwt_log_info "validated block %a"
+                          Block_hash.pp_short hash >>= fun () ->
                         Protocol_validator.prefetch_and_compile_protocols
                           bv.protocol_validator
                           ?peer ~timeout:bv.protocol_timeout
diff --git a/lib_node_shell/state.ml b/lib_node_shell/state.ml
index 33b5c94fc..d0d901b25 100644
--- a/lib_node_shell/state.ml
+++ b/lib_node_shell/state.ml
@@ -441,6 +441,22 @@ module Block = struct
       read_exn net_state header.shell.predecessor >>= fun block ->
       Lwt.return (Some block)
 
+  type error += Inconsistent_hash of Context_hash.t * Context_hash.t
+
+  let () =
+    Error_monad.register_error_kind
+      `Permanent
+      ~id:"inconsistentContextHash"
+      ~title:"Inconsistent commit hash"
+      ~description:
+        "When commiting the context of a block, the announced context \
+         hash was not the one computed at commit time."
+      Data_encoding.(obj2
+                       (req "wrong_context_hash" Context_hash.encoding)
+                       (req "expected_context_hash" Context_hash.encoding))
+      (function Inconsistent_hash (got, exp) -> Some (got, exp) | _ -> None)
+      (fun (got, exp) -> Inconsistent_hash (got, exp))
+
   let store
       net_state block_header operations
       { Updater.context ; message ; max_operations_ttl ;
@@ -457,6 +473,9 @@ module Block = struct
       else begin
         Context.commit
           ~time:block_header.shell.timestamp ?message context >>= fun commit ->
+        fail_unless
+          (Context_hash.equal block_header.shell.context commit)
+          (Inconsistent_hash (commit, block_header.shell.context)) >>=? fun () ->
         let contents = {
           Store.Block.header = block_header ;
           message ;
@@ -544,7 +563,7 @@ module Block = struct
   let context { net_state ; hash } =
     Shared.use net_state.block_store begin fun block_store ->
       Store.Block.Contents.read_exn (block_store, hash)
-    end  >>= fun { context = commit } ->
+    end >>= fun { context = commit } ->
     Shared.use net_state.context_index begin fun context_index ->
       Context.checkout_exn context_index commit
     end
diff --git a/lib_node_shell/state.mli b/lib_node_shell/state.mli
index d341410fe..fc649eacc 100644
--- a/lib_node_shell/state.mli
+++ b/lib_node_shell/state.mli
@@ -104,6 +104,8 @@ module Block : sig
   val read_opt: Net.t -> Block_hash.t -> block option Lwt.t
   val read_exn: Net.t -> Block_hash.t -> block Lwt.t
 
+  type error += Inconsistent_hash of Context_hash.t * Context_hash.t
+
   val store:
     Net.t ->
     Block_header.t ->