From 169ae695d9496e9ca9bde88687db05662fb23f65 Mon Sep 17 00:00:00 2001
From: Herr Seppia <seppia@dusk.network>
Date: Wed, 18 Dec 2024 16:11:25 +0100
Subject: [PATCH] rusk: change session opening to verify TIP instead of open
 old commits

---
 rusk/src/lib/error.rs     |  5 +++++
 rusk/src/lib/node/rusk.rs |  5 ++++-
 rusk/src/lib/node/vm.rs   | 16 ++++++++++++----
 3 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/rusk/src/lib/error.rs b/rusk/src/lib/error.rs
index 39ea449b83..fdacc66250 100644
--- a/rusk/src/lib/error.rs
+++ b/rusk/src/lib/error.rs
@@ -58,6 +58,8 @@ pub enum Error {
     InvalidCreditsCount(u64, usize),
     /// Memo too large
     MemoTooLarge(usize),
+    /// Chain tip different from the expected one
+    TipChanged,
 }
 
 impl std::error::Error for Error {}
@@ -182,6 +184,9 @@ impl fmt::Display for Error {
             Error::MemoTooLarge(size) => {
                 write!(f, "The memo size {size} is too large")
             }
+            Error::TipChanged => {
+                write!(f, "Chain tip different from the expected one")
+            }
         }
     }
 }
diff --git a/rusk/src/lib/node/rusk.rs b/rusk/src/lib/node/rusk.rs
index bc0b72fcd7..878c739dc4 100644
--- a/rusk/src/lib/node/rusk.rs
+++ b/rusk/src/lib/node/rusk.rs
@@ -479,7 +479,10 @@ impl Rusk {
         block_height: u64,
         commit: [u8; 32],
     ) -> Result<Session> {
-        let mut session = self._session(block_height, Some(commit))?;
+        let mut session = self._session(block_height, None)?;
+        if session.root() != commit {
+            return Err(Error::TipChanged);
+        }
         let _: CallReceipt<()> = session
             .call(STAKE_CONTRACT, "before_state_transition", &(), u64::MAX)
             .expect("before_state_transition to success");
diff --git a/rusk/src/lib/node/vm.rs b/rusk/src/lib/node/vm.rs
index 87da365186..0f60abb2db 100644
--- a/rusk/src/lib/node/vm.rs
+++ b/rusk/src/lib/node/vm.rs
@@ -6,6 +6,7 @@
 
 mod query;
 
+use dusk_consensus::errors::VstError;
 use node_data::events::contract::ContractEvent;
 use tracing::info;
 
@@ -48,13 +49,14 @@ impl VMExecution for Rusk {
         prev_commit: [u8; 32],
         blk: &Block,
         voters: &[Voter],
-    ) -> anyhow::Result<VerificationOutput> {
+    ) -> Result<VerificationOutput, VstError> {
         info!("Received verify_state_transition request");
         let generator = blk.header().generator_bls_pubkey;
         let generator = BlsPublicKey::from_slice(&generator.0)
-            .map_err(|e| anyhow::anyhow!("Error in from_slice {e:?}"))?;
+            .map_err(VstError::InvalidGenerator)?;
 
-        let slashing = Slash::from_block(blk)?;
+        let slashing =
+            Slash::from_block(blk).map_err(VstError::InvalidSlash)?;
 
         let (_, verification_output) = self
             .verify_transactions(
@@ -67,7 +69,13 @@ impl VMExecution for Rusk {
                 slashing,
                 voters,
             )
-            .map_err(|inner| anyhow::anyhow!("Cannot verify txs: {inner}!!"))?;
+            .map_err(|inner| {
+                if let crate::Error::TipChanged = inner {
+                    VstError::TipChanged
+                } else {
+                    VstError::Generic(format!("Cannot verify txs: {inner}!!"))
+                }
+            })?;
 
         Ok(verification_output)
     }