Fix panic in case of invalid checkpoint in chain spec

lib/src/chain_spec.rs

@@ -37,7 +37,7 @@
 use crate::{
     chain::chain_information::{
         build, BabeEpochInformation, ChainInformation, ChainInformationConsensus,
-        ChainInformationFinality, ValidChainInformation,
+        ChainInformationFinality, ValidChainInformation, ValidityError,
     },
     executor, libp2p, trie,
 };
@@ -420,7 +420,9 @@ fn convert_epoch(epoch: &light_sync_state::BabeEpoch) -> BabeEpochInformation {
 }
 
 impl LightSyncState {
-    pub fn to_chain_information(&self) -> ChainInformation {
+    pub fn to_chain_information(&self) -> Result<ValidChainInformation, InvalidCheckpointError> {
+        // TODO: this code is a bit of a shitshow when it comes to corner cases and should be cleaned up after https://github.com/paritytech/substrate/issues/11184
+
         // Create a sorted list of all regular epochs that haven't been pruned from the sync state.
         let mut epochs: Vec<_> = self
             .inner
@@ -442,14 +444,22 @@ impl LightSyncState {
         epochs.dedup_by_key(|(_, epoch)| epoch.epoch_index);
 
         // Get the latest two epochs.
-        let current_epoch = &epochs[epochs.len() - 2].1;
-        let next_epoch = &epochs[epochs.len() - 1].1;
+        let finalized_block_epoch_information = if epochs.len() >= 2 {
+            Some(convert_epoch(epochs[epochs.len() - 2].1))
+        } else {
+            None
+        };
+        if epochs.is_empty() {
+            return Err(InvalidCheckpointError::EmptyBabeEpochsList);
+        }
+        let next_epoch = epochs[epochs.len() - 1].1;
 
         ChainInformation {
             finalized_block_header: self.inner.finalized_block_header.clone(),
             consensus: ChainInformationConsensus::Babe {
-                slots_per_epoch: NonZeroU64::new(current_epoch.duration).unwrap(),
-                finalized_block_epoch_information: Some(convert_epoch(current_epoch)),
+                slots_per_epoch: NonZeroU64::new(next_epoch.duration)
+                    .ok_or(InvalidCheckpointError::InvalidBabeSlotsPerEpoch)?,
+                finalized_block_epoch_information,
                 finalized_next_epoch_transition: convert_epoch(next_epoch),
             },
             finality: ChainInformationFinality::Grandpa {
@@ -459,15 +469,20 @@ impl LightSyncState {
                         .grandpa_authority_set
                         .current_authorities
                         .iter()
-                        .map(|authority| crate::header::GrandpaAuthority {
-                            public_key: authority.public_key,
-                            weight: NonZeroU64::new(authority.weight).unwrap(),
+                        .map(|authority| {
+                            Ok(crate::header::GrandpaAuthority {
+                                public_key: authority.public_key,
+                                weight: NonZeroU64::new(authority.weight)
+                                    .ok_or(InvalidCheckpointError::InvalidGrandpaAuthorityWeight)?,
+                            })
                         })
-                        .collect()
+                        .collect::<Result<_, _>>()?
                 },
                 finalized_scheduled_change: None, // TODO: unimplemented
             },
         }
+        .try_into()
+        .map_err(InvalidCheckpointError::InvalidData)
     }
 }
 
@@ -500,6 +515,20 @@ pub enum FromGenesisStorageError {
     UnknownStorageItems,
 }
 
+/// Error when building the chain information from the genesis storage.
+#[derive(Debug, derive_more::Display)]
+pub enum InvalidCheckpointError {
+    /// The list of Babe epochs is empty.
+    EmptyBabeEpochsList,
+    /// Found a value of 0 for the number of Babe slots per epoch.
+    InvalidBabeSlotsPerEpoch,
+    /// Found a Grandpa authority with a weight of 0.
+    InvalidGrandpaAuthorityWeight,
+    /// Information found in the checkpoint is invalid.
+    #[display(fmt = "{_0}")]
+    InvalidData(ValidityError),
+}
+
 #[cfg(test)]
 mod tests {
     use super::{Bootnode, ChainSpec};

light-base/src/lib.rs

@@ -79,8 +79,7 @@ use futures_util::{future, FutureExt as _};
 use hashbrown::{hash_map::Entry, HashMap};
 use itertools::Itertools as _;
 use smoldot::{
-    chain::{self, chain_information},
-    chain_spec, header,
+    chain, chain_spec, header,
     informant::HashDisplay,
     libp2p::{connection, multiaddr, peer_id},
 };
@@ -363,11 +362,9 @@ impl<TPlat: platform::PlatformRef, TChain> Client<TPlat, TChain> {
         let (chain_information, genesis_block_header, checkpoint_nodes) = {
             match (
                 chain_spec.to_chain_information().map(|(ci, _)| ci), // TODO: don't just throw away the runtime
-                chain_spec.light_sync_state().map(|s| {
-                    chain::chain_information::ValidChainInformation::try_from(
-                        s.to_chain_information(),
-                    )
-                }),
+                chain_spec
+                    .light_sync_state()
+                    .map(|s| s.to_chain_information()),
                 database::decode_database(
                     config.database_content,
                     chain_spec.block_number_bytes().into(),
@@ -1012,7 +1009,7 @@ pub enum AddChainError {
     ChainSpecNeitherGenesisStorageNorCheckpoint,
     /// Checkpoint provided in the chain specification is invalid.
     #[display(fmt = "Invalid checkpoint in chain specification: {_0}")]
-    InvalidCheckpoint(chain_information::ValidityError),
+    InvalidCheckpoint(chain_spec::InvalidCheckpointError),
     /// Failed to build the information about the chain from the genesis storage. This indicates
     /// invalid data in the genesis storage.
     #[display(fmt = "Failed to build genesis chain information: {_0}")]

wasm-node/CHANGELOG.md

@@ -2,6 +2,11 @@
 
 ## Unreleased
 
+### Fixed
+
+- Fix panic when the checkpoint in the chain specification contains an empty list of Babe epochs, which can normally only happen if the checkpoint was modified manually. ([#603](https://github.com/smol-dot/smoldot/pull/603))
+- Fix panic when the checkpoint in the chain specification contains only one Babe epoch, which can happen if the checkpoint was generated before any block was authored. ([#603](https://github.com/smol-dot/smoldot/pull/603))
+
 ## 1.0.6 - 2023-05-09
 
 ### Changed