From 72e5122e73ef981a1cd95d97aac1f1cf7de1f691 Mon Sep 17 00:00:00 2001
From: Federico Gimenez <fgimenez@users.noreply.github.com>
Date: Wed, 8 May 2024 15:21:16 +0200
Subject: [PATCH] fix: prevents potential arithmetic underflow (#8156)

---
 crates/blockchain-tree/src/chain.rs            | 3 ++-
 crates/interfaces/src/blockchain_tree/error.rs | 6 +++++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/crates/blockchain-tree/src/chain.rs b/crates/blockchain-tree/src/chain.rs
index 637ea52e7e..db4b4627ab 100644
--- a/crates/blockchain-tree/src/chain.rs
+++ b/crates/blockchain-tree/src/chain.rs
@@ -119,7 +119,8 @@ impl AppendableChain {
         DB: Database + Clone,
         E: BlockExecutorProvider,
     {
-        let parent_number = block.number - 1;
+        let parent_number =
+            block.number.checked_sub(1).ok_or(BlockchainTreeError::GenesisBlockHasNoParent)?;
         let parent = self.blocks().get(&parent_number).ok_or(
             BlockchainTreeError::BlockNumberNotFoundInChain { block_number: parent_number },
         )?;
diff --git a/crates/interfaces/src/blockchain_tree/error.rs b/crates/interfaces/src/blockchain_tree/error.rs
index e9cdb8714d..a98d765014 100644
--- a/crates/interfaces/src/blockchain_tree/error.rs
+++ b/crates/interfaces/src/blockchain_tree/error.rs
@@ -47,6 +47,9 @@ pub enum BlockchainTreeError {
         /// The block hash of the block that failed to buffer.
         block_hash: BlockHash,
     },
+    /// Thrown when trying to access genesis parent.
+    #[error("genesis block has no parent")]
+    GenesisBlockHasNoParent,
 }
 
 /// Canonical Errors
@@ -318,7 +321,8 @@ impl InsertBlockErrorKind {
                     BlockchainTreeError::CanonicalChain { .. } |
                     BlockchainTreeError::BlockNumberNotFoundInChain { .. } |
                     BlockchainTreeError::BlockHashNotFoundInChain { .. } |
-                    BlockchainTreeError::BlockBufferingFailed { .. } => false,
+                    BlockchainTreeError::BlockBufferingFailed { .. } |
+                    BlockchainTreeError::GenesisBlockHasNoParent => false,
                 }
             }
             InsertBlockErrorKind::Provider(_) | InsertBlockErrorKind::Internal(_) => {