From 384ab0ceddd25b5b31722fe639229c0ecf554926 Mon Sep 17 00:00:00 2001
From: Stan Bondi <sdbondi@users.noreply.github.com>
Date: Thu, 24 Mar 2022 16:06:40 +0400
Subject: [PATCH] fix(sync): ban peer if sending invalid prev_header (#3955)

Description
---
- bans peer for ChainLinkBroken error

Motivation and Context
---
Node should not continue syncing from a peer that does not properly link headers

How Has This Been Tested?
---
Manually, my node banned peers that sent an incorrect prev header
---
 .../src/base_node/sync/header_sync/error.rs   |  8 ++++++--
 .../sync/header_sync/synchronizer.rs          | 19 +++++++++++++++++++
 .../base_node/sync/header_sync/validator.rs   |  1 +
 3 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/base_layer/core/src/base_node/sync/header_sync/error.rs b/base_layer/core/src/base_node/sync/header_sync/error.rs
index a81948dbb8..c744c5e4c5 100644
--- a/base_layer/core/src/base_node/sync/header_sync/error.rs
+++ b/base_layer/core/src/base_node/sync/header_sync/error.rs
@@ -67,8 +67,12 @@ pub enum BlockHeaderSyncError {
     NetworkSilence,
     #[error("Invalid protocol response: {0}")]
     InvalidProtocolResponse(String),
-    #[error("Headers did not form a chain. Expected {actual} to equal the previous hash {expected}")]
-    ChainLinkBroken { actual: String, expected: String },
+    #[error("Header at height {height} did not form a chain. Expected {actual} to equal the previous hash {expected}")]
+    ChainLinkBroken {
+        height: u64,
+        actual: String,
+        expected: String,
+    },
     #[error("Block error: {0}")]
     BlockError(#[from] BlockError),
     #[error(
diff --git a/base_layer/core/src/base_node/sync/header_sync/synchronizer.rs b/base_layer/core/src/base_node/sync/header_sync/synchronizer.rs
index 860b52bfaa..da6a073dd8 100644
--- a/base_layer/core/src/base_node/sync/header_sync/synchronizer.rs
+++ b/base_layer/core/src/base_node/sync/header_sync/synchronizer.rs
@@ -180,6 +180,19 @@ impl<'a, B: BlockchainBackend + 'static> HeaderSynchronizer<'a, B> {
                     })
                     .await?;
                 },
+                Err(BlockHeaderSyncError::ChainLinkBroken {
+                    height,
+                    actual,
+                    expected,
+                }) => {
+                    let reason = BanReason::ChainLinkBroken {
+                        height,
+                        actual: actual.to_string(),
+                        expected: expected.to_string(),
+                    };
+                    warn!(target: LOG_TARGET, "Chain link broken: {}", reason);
+                    self.ban_peer_long(node_id, reason).await?;
+                },
                 Err(ref err @ BlockHeaderSyncError::WeakerChain { claimed, actual, local }) => {
                     warn!(target: LOG_TARGET, "{}", err);
                     self.ban_peer_long(node_id, BanReason::PeerCouldNotProvideStrongerChain {
@@ -794,6 +807,12 @@ enum BanReason {
         "Peer claimed an accumulated difficulty of {claimed} but validated difficulty was {actual} <= local: {local}"
     )]
     PeerCouldNotProvideStrongerChain { claimed: u128, actual: u128, local: u128 },
+    #[error("Header at height {height} did not form a chain. Expected {actual} to equal the previous hash {expected}")]
+    ChainLinkBroken {
+        height: u64,
+        actual: String,
+        expected: String,
+    },
 }
 
 struct ChainSplitInfo {
diff --git a/base_layer/core/src/base_node/sync/header_sync/validator.rs b/base_layer/core/src/base_node/sync/header_sync/validator.rs
index 84f3c263e8..ca7cdcc28c 100644
--- a/base_layer/core/src/base_node/sync/header_sync/validator.rs
+++ b/base_layer/core/src/base_node/sync/header_sync/validator.rs
@@ -129,6 +129,7 @@ impl<B: BlockchainBackend + 'static> BlockHeaderSyncValidator<B> {
         }
         if header.prev_hash != state.previous_accum.hash {
             return Err(BlockHeaderSyncError::ChainLinkBroken {
+                height: header.height,
                 actual: header.prev_hash.to_hex(),
                 expected: state.previous_accum.hash.to_hex(),
             });