Congress_Buggy.v 17.2 KB
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From Coq Require Import ZArith.
From Coq Require Import Morphisms.
From Coq Require Import Psatz.
From Coq Require Import Permutation.
From SmartContracts Require Import Blockchain.
From SmartContracts Require Import Oak.
From SmartContracts Require Import Monads.
From SmartContracts Require Import Containers.
From SmartContracts Require Import Automation.
From SmartContracts Require Import Extras.
From SmartContracts Require Import BoundedN.
From RecordUpdate Require Import RecordUpdate.
From Coq Require Import List.

Import ListNotations.
Import RecordSetNotations.

Section CongressBuggy.
Context {BaseTypes : ChainBase}.

Local Open Scope Z.
Set Primitive Projections.

Definition ProposalId := nat.

Inductive CongressAction :=
  | cact_transfer (to : Address) (amount : Amount)
  | cact_call (to : Address) (amount : Amount) (msg : OakValue).

Record Proposal :=
  build_proposal {
    actions : list CongressAction;
    votes : FMap Address Z;
    vote_result : Z;
    proposed_in : nat;
  }.

Instance proposal_settable : Settable _ :=
  settable! build_proposal <actions; votes; vote_result; proposed_in>.

Record Rules :=
  build_rules {
    min_vote_count_permille : Z;
    margin_needed_permille : Z;
    debating_period_in_blocks : nat;
  }.

Record Setup :=
  build_setup {
    setup_rules : Rules;
  }.

Inductive Msg :=
  | transfer_ownership : Address -> Msg
  | change_rules : Rules -> Msg
  | add_member : Address -> Msg
  | remove_member : Address -> Msg
  | create_proposal : list CongressAction -> Msg
  | vote_for_proposal : ProposalId -> Msg
  | vote_against_proposal : ProposalId -> Msg
  | retract_vote : ProposalId -> Msg
  | finish_proposal : ProposalId -> Msg
  | finish_proposal_remove : ProposalId -> Msg.

Record State :=
  build_state {
    owner : Address;
    state_rules : Rules;
    proposals : FMap nat Proposal;
    next_proposal_id : ProposalId;
    members : FMap Address unit;
  }.

Instance state_settable : Settable _ :=
  settable! build_state <owner; state_rules; proposals; next_proposal_id; members>.

Section Equivalences.

Definition deserialize_rules (v : OakValue) : option Rules :=
  do '((a, b), c) <- deserialize v;
  Some (build_rules a b c).

Global Program Instance rules_equivalence : OakTypeEquivalence Rules :=
  {| serialize r := let (a, b, c) := r in serialize (a, b, c);
     (* Why does
     deserialize v :=
       do '((a, b), c) <- deserialize v;
       Some (build_rules a b c); |}.
       not work here? *)
     deserialize := deserialize_rules; |}.
Next Obligation.
  intros x. unfold deserialize_rules.
  rewrite deserialize_serialize.
  reflexivity.
Qed.

Global Program Instance setup_equivalence : OakTypeEquivalence Setup :=
  {| serialize s := serialize s.(setup_rules);
     deserialize or :=
       do rules <- deserialize or;
       Some (build_setup rules); |}.
Next Obligation.
  intros x.
  simpl.
  rewrite deserialize_serialize.
  reflexivity.
Qed.

Definition deserialize_congress_action (v : OakValue) : option CongressAction :=
  do val <- deserialize v;
  Some (match val with
  | inl (to, amount) => cact_transfer to amount
  | inr (to, amount, msg) => cact_call to amount msg
  end).

Global Program Instance congress_action_equivalence : OakTypeEquivalence CongressAction :=
  {| serialize ca :=
       serialize
         match ca with
         | cact_transfer to amount => inl (to, amount)
         | cact_call to amount msg => inr (to, amount, msg)
         end;
     deserialize := deserialize_congress_action; |}.
Next Obligation.
  intros ca.
  unfold deserialize_congress_action.
  rewrite deserialize_serialize.
  destruct ca; reflexivity.
Qed.

Definition deserialize_proposal (v : OakValue) : option Proposal :=
  do '(a, b, c, d) <- deserialize v;
  Some (build_proposal a b c d).

Global Program Instance proposal_equivalence : OakTypeEquivalence Proposal :=
  {| serialize p :=
       let (a, b, c, d) := p in
       serialize (a, b, c, d);
     deserialize := deserialize_proposal;
  |}.
Next Obligation.
  intros p.
  unfold deserialize_proposal.
  rewrite deserialize_serialize.
  destruct p; reflexivity.
Qed.

Definition serialize_msg (m : Msg) : OakValue :=
  serialize
    match m with
    | transfer_ownership a => (0, serialize a)
    | change_rules r => (1, serialize r)
    | add_member a => (2, serialize a)
    | remove_member a => (3, serialize a)
    | create_proposal l => (4, serialize l)
    | vote_for_proposal pid => (5, serialize pid)
    | vote_against_proposal pid => (6, serialize pid)
    | retract_vote pid => (7, serialize pid)
    | finish_proposal pid => (8, serialize pid)
    | finish_proposal_remove pid => (9, serialize pid)
    end.

Definition deserialize_msg (v : OakValue) : option Msg :=
  do '(tag, v) <- deserialize v;
  match tag with
  | 0 => option_map transfer_ownership (deserialize v)
  | 1 => option_map change_rules (deserialize v)
  | 2 => option_map add_member (deserialize v)
  | 3 => option_map remove_member (deserialize v)
  | 4 => option_map create_proposal (deserialize v)
  | 5 => option_map vote_for_proposal (deserialize v)
  | 6 => option_map vote_against_proposal (deserialize v)
  | 7 => option_map retract_vote (deserialize v)
  | 8 => option_map finish_proposal (deserialize v)
  | 9 => option_map finish_proposal_remove (deserialize v)
  | _ => None
  end.

Global Program Instance msg_equivalence : OakTypeEquivalence Msg :=
  {| serialize := serialize_msg; deserialize := deserialize_msg; |}.
Next Obligation.
  intros msg.
  unfold serialize_msg, deserialize_msg.
  destruct msg; repeat (simpl; rewrite deserialize_serialize); reflexivity.
Qed.

Definition serialize_state (s : State) : OakValue :=
  let (a, b, c, d, e) := s in
  serialize (a, b, c, d, e).

Definition deserialize_state (v : OakValue) : option State :=
  do '(a, b, c, d, e) <- deserialize v;
  Some (build_state a b c d e).

Global Program Instance state_equivalence : OakTypeEquivalence State :=
  {| serialize := serialize_state; deserialize := deserialize_state; |}.
Next Obligation.
  unfold serialize_state, deserialize_state.
  destruct x; repeat (simpl; rewrite deserialize_serialize); reflexivity.
Qed.

End Equivalences.

Definition validate_rules (rules : Rules) : bool :=
    (rules.(min_vote_count_permille) >=? 0)
        && (rules.(min_vote_count_permille) <=? 1000)
        && (rules.(margin_needed_permille) >=? 0)
        && (rules.(margin_needed_permille) <=? 1000)
        && (0 <=? rules.(debating_period_in_blocks))%nat.

Definition init
           (chain : Chain)
           (ctx : ContractCallContext)
           (setup : Setup) : option State :=
  if validate_rules setup.(setup_rules) then
    Some {| owner := ctx.(ctx_from);
            state_rules := setup.(setup_rules);
            proposals := FMap.empty;
            next_proposal_id := 1%nat;
            members := FMap.empty |}
  else
    None.

Definition add_proposal (actions : list CongressAction) (chain : Chain) (state : State) : State :=
  let id := state.(next_proposal_id) in
  let slot_num := chain.(block_header).(slot_number) in
  let proposal := {| actions := actions;
                     votes := FMap.empty;
                     vote_result := 0;
                     proposed_in := slot_num |} in
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  state<|proposals ::= FMap.add id proposal|>
       <|next_proposal_id ::= S|>.
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Definition vote_on_proposal
           (voter : Address)
           (pid : ProposalId)
           (vote : Z)
           (state : State)
  : option State :=
  do proposal <- FMap.find pid state.(proposals);
  let old_vote := match FMap.find voter proposal.(votes) with
                 | Some old => old
                 | None => 0
                 end in
  let new_votes := FMap.add voter vote proposal.(votes) in
  let new_vote_result := proposal.(vote_result) - old_vote + vote in
  let new_proposal :=
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      proposal<|votes := new_votes|>
              <|vote_result := new_vote_result|> in
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  Some (state<|proposals ::= FMap.add pid new_proposal|>).

Definition do_retract_vote
           (voter : Address)
           (pid : ProposalId)
           (state : State)
  : option State :=
  do proposal <- FMap.find pid state.(proposals);
  do old_vote <- FMap.find voter proposal.(votes);
  let new_votes := FMap.remove voter proposal.(votes) in
  let new_vote_result := proposal.(vote_result) - old_vote in
  let new_proposal :=
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      proposal<|votes := new_votes|>
              <|vote_result := new_vote_result|> in
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  Some (state<|proposals ::= FMap.add pid new_proposal|>).

Definition congress_action_to_chain_action (act : CongressAction) : ActionBody :=
  match act with
  | cact_transfer to amt => act_transfer to amt
  | cact_call to amt msg => act_call to amt msg
  end.

Definition proposal_passed (proposal : Proposal) (state : State) : bool :=
  let rules := state.(state_rules) in
  let total_votes_for_proposal := Z.of_nat (FMap.size proposal.(votes)) in
  let total_members := Z.of_nat (FMap.size state.(members)) in
  let aye_votes := (proposal.(vote_result) + total_votes_for_proposal) / 2 in
  let vote_count_permille := total_votes_for_proposal * 1000 / total_members in
  let aye_permille := aye_votes * 1000 / total_votes_for_proposal in
  let enough_voters := vote_count_permille >=? rules.(min_vote_count_permille) in
  let enough_ayes := aye_permille >=? rules.(margin_needed_permille) in
  enough_voters && enough_ayes.

Definition do_finish_proposal
           (ctx : ContractCallContext)
           (pid : ProposalId)
           (state : State)
           (chain : Chain)
  : option (State * list ActionBody) :=
  do proposal <- FMap.find pid state.(proposals);
  let rules := state.(state_rules) in
  let debate_end := (proposal.(proposed_in) + rules.(debating_period_in_blocks))%nat in
  let cur_slot := chain.(block_header).(slot_number) in
  if (cur_slot <? debate_end)%nat then
    None
  else
    let response_acts :=
        if proposal_passed proposal state
        then proposal.(actions)
        else [] in
    let response_chain_acts := map congress_action_to_chain_action response_acts in
    let self_call_msg := serialize (finish_proposal_remove pid) in
    let self_call := act_call (ctx_contract_address ctx) 0 self_call_msg in
    Some (state, response_chain_acts ++ [self_call]).

Definition receive
           (chain : Chain)
           (ctx : ContractCallContext)
           (state : State)
           (maybe_msg : option Msg)
  : option (State * list ActionBody) :=
  let sender := ctx.(ctx_from) in
  let is_from_owner := (sender =? state.(owner))%address in
  let is_from_member := FMap.mem sender state.(members) in
  let without_actions := option_map (fun new_state => (new_state, [])) in
  match maybe_msg, is_from_owner, is_from_member with
  | Some (transfer_ownership new_owner), true, _ =>
    Some (state<|owner := new_owner|>, [])

  | Some (change_rules new_rules), true, _ =>
    if validate_rules new_rules then
      Some (state<|state_rules := new_rules|>, [])
    else
      None

  | Some (add_member new_member), true, _ =>
    Some (state<|members ::= FMap.add new_member tt|>, [])

  | Some (remove_member old_member), true, _ =>
    Some (state<|members ::= FMap.remove old_member|>, [])

  | Some (create_proposal actions), _, true =>
    Some (add_proposal actions chain state, [])

  | Some (vote_for_proposal pid), _, true =>
    without_actions (vote_on_proposal sender pid 1 state)

  | Some (vote_against_proposal pid), _, true =>
    without_actions (vote_on_proposal sender pid (-1) state)

  | Some (retract_vote pid), _, true =>
    without_actions (do_retract_vote sender pid state)

  | Some (finish_proposal pid), _, _ =>
    do_finish_proposal ctx pid state chain

  | Some (finish_proposal_remove pid), _, _ =>
    if (sender =? ctx_contract_address ctx)%address then
      Some (state<|proposals ::= FMap.remove pid|>, [])
    else
      None

  | _, _, _ =>
        None

  end.

Ltac solve_contract_proper :=
  repeat
    match goal with
    | [|- ?x _  = ?x _] => unfold x
    | [|- ?x _ _ = ?x _ _] => unfold x
    | [|- ?x _ _ _ = ?x _ _ _] => unfold x
    | [|- ?x _ _ _ _ = ?x _ _ _ _] => unfold x
    | [|- ?x _ _ _ _ = ?x _ _ _ _] => unfold x
    | [|- ?x _ _ _ _ _ = ?x _ _ _ _ _] => unfold x
    | [|- Some _ = Some _] => f_equal
    | [|- pair _ _ = pair _ _] => f_equal
    | [|- (if ?x then _ else _) = (if ?x then _ else _)] => destruct x
    | [|- match ?x with | _ => _ end = match ?x with | _ => _ end ] => destruct x
    | [H: ChainEquiv _ _ |- _] => rewrite H in *
    | _ => subst; auto
    end.

Lemma init_proper :
  Proper (ChainEquiv ==> eq ==> eq ==> eq) init.
Proof. repeat intro; solve_contract_proper. Qed.

Lemma receive_proper :
  Proper (ChainEquiv ==> eq ==> eq ==> eq ==> eq) receive.
Proof. repeat intro; solve_contract_proper. Qed.

Definition contract : Contract Setup Msg State :=
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  build_contract init init_proper receive receive_proper.
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End CongressBuggy.
(* We will show that this contract is buggy and does not satisfy the
   property we proved for the other version of the Congress. We do
   this with a counterexample, where we exploit reentrancy similar to
   the DAO hack. We first define a contract that does this
   exploitation. *)

Section ExploitContract.
Context {Base : ChainBase}.

Definition ExploitSetup := unit.
Definition ExploitState := nat. (* how many times have we called ourselves *)
Definition ExploitMsg := unit.
Definition exploit_init
            (chain : Chain)
            (ctx : ContractCallContext)
            (setup : ExploitSetup) : option ExploitState :=
  Some 0.
Definition exploit_receive
            (chain : Chain)
            (ctx : ContractCallContext)
            (state : ExploitState)
            (msg : option ExploitMsg) : option (ExploitState * list ActionBody) :=
  if 25 <? state then
    Some (state, [])
  else
    let again := finish_proposal 1 in
    Some (S state, [act_call (ctx_from ctx) 0 (serialize again)]).

Instance exploit_init_proper :
  Proper (ChainEquiv ==> eq ==> eq ==> eq) exploit_init.
Proof. now subst. Qed.

Instance exploit_receive_proper :
  Proper (ChainEquiv ==> eq ==> eq ==> eq ==> eq) exploit_receive.
Proof. now subst. Qed.

Definition exploit_contract : Contract ExploitSetup ExploitMsg ExploitState :=
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  build_contract exploit_init exploit_init_proper exploit_receive exploit_receive_proper.
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End ExploitContract.

(* With this defined we can give the counterexample with relative ease. We use a
concrete implementation of a blockchain for this. *)
From SmartContracts Require LocalBlockchain.

Section Theories.
  Import LocalBlockchain.

  Open Scope nat.
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  Definition num_acts_created_in_proposals (txs : list Tx) :=
  let count tx :=
      match tx_body tx with
      | tx_call (Some msg) =>
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        match deserialize msg : option Msg with
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        | Some (create_proposal acts) => length acts
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        | _ => 0
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        end
      | _ => 0
      end in
  sumnat count txs.
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  Definition exploit_example : option (Address * LocalChainBuilderDepthFirst) :=
    let chain := builder_initial in
    let baker := BoundedN.of_Z_const AddrSize 10 in
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    let add_block (chain : LocalChainBuilderDepthFirst) act_bodies :=
        let next_header :=
            (block_header chain)<|block_height ::= S|><|slot_number ::= S|> in
        let acts := map (build_act baker) act_bodies in
        builder_add_block chain baker next_header acts in
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    (* Get some money on the baker *)
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    do chain <- add_block chain [];
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    (* Deploy congress and exploit contracts *)
    let rules :=
        {| min_vote_count_permille := 200;
           margin_needed_permille := 501;
           debating_period_in_blocks := 0; |} in
    let dep_congress := create_deployment 50 contract {| setup_rules := rules |} in
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    let dep_exploit := create_deployment 0 exploit_contract tt in
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    do chain <- add_block chain [dep_congress; dep_exploit];
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    let contracts := map fst (FMap.elements (lc_contracts (lcb_lc chain))) in
    let exploit := nth 0 contracts baker in
    let congress := nth 1 contracts baker in
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    (* Add baker to congress, create a proposal to transfer *)
    (* some money to exploit contract, vote for the proposal, and execute the proposal *)
    let add_baker := add_member baker in
    let create_proposal := create_proposal [cact_transfer exploit 1] in
    let vote_proposal := vote_for_proposal 1 in
    let exec_proposal := finish_proposal 1 in
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    let act_bodies :=
        map (fun m => act_call congress 0 (serialize m))
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            [add_baker; create_proposal; vote_proposal; exec_proposal] in
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    do chain <- add_block chain act_bodies;
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    Some (congress, chain).

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  Definition unpacked_exploit_example : Address * LocalChainBuilderDepthFirst :=
    unpack_option exploit_example.
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  (* Now we prove that this version of the contract is buggy, i.e. it does not satisfy the
     property we proved for the other version of the Congress. We filter out transactions
     from the congress to the congress as we have those now (due to self calls). *)
  Theorem congress_is_buggy :
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    exists state addr (trace : ChainTrace empty_state state),
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      env_contracts state addr = Some (contract : WeakContract) /\
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      length (filter (fun tx => negb (tx_to tx =? addr)%address) (outgoing_txs trace addr)) >
      num_acts_created_in_proposals (incoming_txs trace addr).
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  Proof.
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    exists (build_chain_state (snd unpacked_exploit_example) []).
    exists (fst unpacked_exploit_example).
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    exists (builder_trace (snd unpacked_exploit_example)).
    split.
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    - reflexivity.
    - vm_compute.
      lia.
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  Qed.
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End Theories.