From 96dd65e36dac44e561bef5eb6a2a70574eb134dc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Gr=C3=A9goire=20Henry?= <gregoire.henry@tezos.com>
Date: Thu, 10 May 2018 16:57:58 +0200
Subject: [PATCH] Shell: early detection of incompatible injected blocks

---
 src/lib_shell/chain_validator.ml | 41 +++++++++++++++++++++-----------
 src/lib_shell/state.ml           |  5 ++++
 src/lib_shell/state.mli          |  7 ++++++
 3 files changed, 39 insertions(+), 14 deletions(-)

diff --git a/src/lib_shell/chain_validator.ml b/src/lib_shell/chain_validator.ml
index b695adba5..114b303f5 100644
--- a/src/lib_shell/chain_validator.ml
+++ b/src/lib_shell/chain_validator.ml
@@ -408,22 +408,35 @@ let child w =
       try Some (List.assoc (State.Chain.id chain_state) (Worker.list table))
       with Not_found -> None
 
-let validate_block w ?(force = false) hash block operations =
+let assert_fitness_increases ?(force = false) w distant_header =
+  let pv = Worker.state w in
+  let chain_state = Distributed_db.chain_state pv.parameters.chain_db in
+  Chain.head chain_state >>= fun local_header ->
+  fail_when
+    (not force &&
+     Fitness.compare
+       distant_header.Block_header.shell.fitness
+       (State.Block.fitness local_header) <= 0)
+    (failure "Fitness too low")
+
+let assert_checkpoint w hash (header: Block_header.t) =
+  let pv = Worker.state w in
+  let chain_state = Distributed_db.chain_state pv.parameters.chain_db in
+  State.Chain.acceptable_block chain_state hash header >>= fun acceptable ->
+  fail_unless acceptable
+    (Validation_errors.Checkpoint_error (hash, None))
+
+let validate_block w ?force hash block operations =
   let nv = Worker.state w in
   assert (Block_hash.equal hash (Block_header.hash block)) ;
-  Chain.head nv.parameters.chain_state >>= fun head ->
-  let head = State.Block.header head in
-  if
-    force || Fitness.(head.shell.fitness < block.shell.fitness)
-  then
-    Block_validator.validate
-      ~canceler:(Worker.canceler w)
-      ~notify_new_block:(notify_new_block w)
-      nv.parameters.block_validator
-      nv.parameters.chain_db
-      hash block operations
-  else
-    failwith "Fitness too low"
+  assert_fitness_increases ?force w block >>=? fun () ->
+  assert_checkpoint w hash block >>=? fun () ->
+  Block_validator.validate
+    ~canceler:(Worker.canceler w)
+    ~notify_new_block:(notify_new_block w)
+    nv.parameters.block_validator
+    nv.parameters.chain_db
+    hash block operations
 
 let bootstrapped w =
   let { bootstrapped_waiter } = Worker.state w in
diff --git a/src/lib_shell/state.ml b/src/lib_shell/state.ml
index 83aa18358..45f75c645 100644
--- a/src/lib_shell/state.ml
+++ b/src/lib_shell/state.ml
@@ -571,6 +571,11 @@ module Chain = struct
       end
     end
 
+  let acceptable_block chain_state hash (header : Block_header.t) =
+    Shared.use chain_state.chain_data begin fun chain_data ->
+      Locked_block.acceptable chain_data hash header
+    end
+
   let destroy state chain =
     lwt_debug "destroy %a" Chain_id.pp (id chain) >>= fun () ->
     Shared.use state.global_data begin fun { global_store ; chains } ->
diff --git a/src/lib_shell/state.mli b/src/lib_shell/state.mli
index 5889419a7..077c6dc9c 100644
--- a/src/lib_shell/state.mli
+++ b/src/lib_shell/state.mli
@@ -84,6 +84,13 @@ module Chain : sig
     Int32.t * Block_hash.t ->
     unit Lwt.t
 
+  (** Check that a block is compatible with the current checkpoint.
+      This function assumes that the predecessor is known valid. *)
+  val acceptable_block:
+    chain_state ->
+    Block_hash.t -> Block_header.t ->
+    bool Lwt.t
+
 end
 
 (** {2 Block database} *****************************************************)