fix: ensure pool_liquidity < DEAD_LIQUIDITY before settling dead_liquidity_reward

Author: bangyro

programs/cp-amm/src/instructions/ix_fund_reward.rs

@@ -77,6 +77,7 @@ pub fn handle_fund_reward(
     let mut pool = ctx.accounts.pool.load_mut()?;
     let current_time = Clock::get()?.unix_timestamp;
     let collect_fee_mode: CollectFeeMode = pool.collect_fee_mode.safe_cast()?;
+    let pool_liquidity = pool.liquidity;
     // 1. update pool rewards
     pool.update_rewards(current_time as u64)?;
 
@@ -98,7 +99,8 @@ pub fn handle_fund_reward(
         reward_info.cumulative_seconds_with_empty_liquidity_reward = 0;
 
         // carry forward dead liquidity reward
-        let dead_liquidity_reward = reward_info.settle_dead_liquidity_reward(collect_fee_mode)?;
+        let dead_liquidity_reward =
+            reward_info.settle_dead_liquidity_reward(pool_liquidity, collect_fee_mode)?;
 
         transfer_fee_excluded_amount_in
             .safe_add(carry_forward_ineligible_reward)?

programs/cp-amm/src/state/pool.rs

@@ -319,25 +319,26 @@ impl RewardInfo {
     /// At that point the reward stops accruing. This is accepted to keep the dead_liquidity_reward_checkpoint at 8 bytes.
     pub fn settle_dead_liquidity_reward(
         &mut self,
+        pool_liquidity: u128,
         collect_fee_mode: CollectFeeMode,
     ) -> Result<u64> {
-        if collect_fee_mode == CollectFeeMode::Compounding {
-            // saturate on overflow
-            let new_dead_liquidity_reward_checkpoint: u64 = safe_mul_shr_256_cast(
-                U256::from(DEAD_LIQUIDITY),
-                self.reward_per_token_stored(),
-                TOTAL_REWARD_SCALE,
-            )
-            .unwrap_or(u64::MAX); // saturate to u64::MAX
-
-            let dead_liquidity_reward = new_dead_liquidity_reward_checkpoint
-                .safe_sub(self.dead_liquidity_reward_checkpoint)?;
-            self.dead_liquidity_reward_checkpoint = new_dead_liquidity_reward_checkpoint;
-
-            Ok(dead_liquidity_reward)
-        } else {
-            Ok(0)
+        if collect_fee_mode != CollectFeeMode::Compounding || pool_liquidity < DEAD_LIQUIDITY {
+            return Ok(0);
         }
+
+        // saturate on overflow
+        let new_dead_liquidity_reward_checkpoint: u64 = safe_mul_shr_256_cast(
+            U256::from(DEAD_LIQUIDITY),
+            self.reward_per_token_stored(),
+            TOTAL_REWARD_SCALE,
+        )
+        .unwrap_or(u64::MAX); // saturate to u64::MAX
+
+        let dead_liquidity_reward =
+            new_dead_liquidity_reward_checkpoint.safe_sub(self.dead_liquidity_reward_checkpoint)?;
+        self.dead_liquidity_reward_checkpoint = new_dead_liquidity_reward_checkpoint;
+
+        Ok(dead_liquidity_reward)
     }
 
     pub fn get_seconds_elapsed_since_last_update(&self, current_time: u64) -> Result<u64> {
@@ -1113,7 +1114,8 @@ impl Pool {
             REWARD_RATE_SCALE,
         )?;
 
-        let dead_liquidity_reward = reward_info.settle_dead_liquidity_reward(collect_fee_mode)?;
+        let dead_liquidity_reward =
+            reward_info.settle_dead_liquidity_reward(self.liquidity, collect_fee_mode)?;
 
         let ineligible_reward = empty_liquidity_reward.safe_add(dead_liquidity_reward)?;