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fix: prevent u64 underflow in validator_claim_fees and use on-chain Rent sysvar #179

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fix: prevent u64 underflow in validator_claim_fees and use on-chain Rent sysvar #179

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23 changes: 16 additions & 7 deletions src/processor/validator_claim_fees.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@ use borsh::BorshDeserialize;
use solana_program::{
account_info::AccountInfo, entrypoint::ProgramResult, msg,
program_error::ProgramError, pubkey::Pubkey, rent::Rent,
sysvar::Sysvar,
};

use crate::{
Expand Down Expand Up @@ -49,18 +50,26 @@ pub fn process_validator_claim_fees(
true,
)?;

// Calculate the amount to transfer
let min_rent = Rent::default().minimum_balance(8);
let amount = args
.amount
.unwrap_or(validator_fees_vault.lamports() - min_rent);
// Use the on-chain Rent sysvar (not `Rent::default()`) and the actual
// account data length so the minimum-balance threshold is always accurate.
let min_rent =
Rent::get()?.minimum_balance(validator_fees_vault.data_len());
Comment on lines +53 to +56
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@coderabbitai coderabbitai Bot May 3, 2026

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⚠️ Potential issue | 🟠 Major | ⚡ Quick win

protocol_claim_fees.rs retains the same unfixed pattern.

src/processor/protocol_claim_fees.rs:53-60 still uses Rent::default().minimum_balance(8) with unchecked subtraction — the exact vulnerability this PR was raised to fix. Consider applying the same Rent::get()?.minimum_balance(fees_vault.data_len()) + checked_sub treatment there before the next release.

🤖 Prompt for AI Agents 
Verify each finding against the current code and only fix it if needed.

In `@src/processor/validator_claim_fees.rs` around lines 53 - 56, The
protocol_claim_fees.rs code still uses Rent::default().minimum_balance(8) and
performs an unchecked subtraction; replace that pattern by retrieving the
on-chain rent with Rent::get()? and computing minimum_balance using the actual
account data length (e.g., fees_vault.data_len()), assign to a min_rent
variable, and use a checked subtraction (checked_sub) when subtracting min_rent
from balances to avoid underflow—locate the logic around fees_vault and the
current minimum_balance/subtraction and update it to mirror the
validator_claim_fees.rs approach.


// Guard against underflow: if the vault somehow holds fewer lamports than
// the rent-exempt minimum, return an error instead of wrapping around.
let available = validator_fees_vault
.lamports()
.checked_sub(min_rent)
.ok_or(ProgramError::InsufficientFunds)?;

let amount = args.amount.unwrap_or(available);

// Ensure vault has enough lamports
if validator_fees_vault.lamports() - min_rent < amount {
if available < amount {
msg!(
"Vault ({}) has insufficient funds: {} < {}",
validator_fees_vault.key,
validator_fees_vault.lamports() - min_rent,
available,
amount
);
return Err(ProgramError::InsufficientFunds);
Expand Down