restricts rent-paying accounts TTL extension

#22292
prevents rent paying accounts creation going forward. However a rent
paying account can linger on for ever if it is continually topped up but
stays below the rent-exempt minimum.
This can prevent eliminating accounts-rewrites and the problematic
rent_epoch field in accounts.

Link to discord discussion:
https://discord.com/channels/428295358100013066/943609352068145162/995202300001927219

This commit restricts rent-paying accounts TTL extension by preventing
increasing lamports on the account if the account stays below the
rent-exempt minimum.

runtime/src/account_rent_state.rs

@@ -14,8 +14,10 @@ pub(crate) enum RentState {
     /// account.lamports == 0
     Uninitialized,
     /// 0 < account.lamports < rent-exempt-minimum
-    /// Parameter is the size of the account data
-    RentPaying(usize),
+    RentPaying {
+        lamports: u64,    // account.lamports()
+        data_size: usize, // account.data().len()
+    },
     /// account.lamports >= rent-exempt-minimum
     RentExempt,
 }
@@ -24,35 +26,54 @@ impl RentState {
     pub(crate) fn from_account(account: &AccountSharedData, rent: &Rent) -> Self {
         if account.lamports() == 0 {
             Self::Uninitialized
-        } else if !rent.is_exempt(account.lamports(), account.data().len()) {
-            Self::RentPaying(account.data().len())
-        } else {
+        } else if rent.is_exempt(account.lamports(), account.data().len()) {
             Self::RentExempt
+        } else {
+            Self::RentPaying {
+                data_size: account.data().len(),
+                lamports: account.lamports(),
+            }
         }
     }
 
-    pub(crate) fn transition_allowed_from(&self, pre_rent_state: &RentState) -> bool {
-        if let Self::RentPaying(post_data_size) = self {
-            if let Self::RentPaying(pre_data_size) = pre_rent_state {
-                post_data_size == pre_data_size // Cannot be RentPaying if resized
-            } else {
-                false // Only RentPaying can continue to be RentPaying
+    pub(crate) fn transition_allowed_from(
+        &self,
+        pre_rent_state: &RentState,
+        restrict_rent_paying_accounts_ttl_extension: bool,
+    ) -> bool {
+        match self {
+            Self::Uninitialized | Self::RentExempt => true,
+            Self::RentPaying {
+                data_size: post_data_size,
+                lamports: post_lamports,
+            } => {
+                match pre_rent_state {
+                    Self::Uninitialized | Self::RentExempt => false,
+                    Self::RentPaying {
+                        data_size: pre_data_size,
+                        lamports: pre_lamports,
+                    } => {
+                        // Cannot be RentPaying if resized
+                        post_data_size == pre_data_size && {
+                            !restrict_rent_paying_accounts_ttl_extension
+                                || post_lamports <= pre_lamports
+                        }
+                    }
+                }
             }
-        } else {
-            true // Post not-RentPaying always ok
         }
     }
 }
 
 pub(crate) fn submit_rent_state_metrics(pre_rent_state: &RentState, post_rent_state: &RentState) {
     match (pre_rent_state, post_rent_state) {
-        (&RentState::Uninitialized, &RentState::RentPaying(_)) => {
+        (&RentState::Uninitialized, &RentState::RentPaying { .. }) => {
             inc_new_counter_info!("rent_paying_err-new_account", 1);
         }
-        (&RentState::RentPaying(_), &RentState::RentPaying(_)) => {
+        (&RentState::RentPaying { .. }, &RentState::RentPaying { .. }) => {
             inc_new_counter_info!("rent_paying_ok-legacy", 1);
         }
-        (_, &RentState::RentPaying(_)) => {
+        (_, &RentState::RentPaying { .. }) => {
             inc_new_counter_info!("rent_paying_err-other", 1);
         }
         _ => {}
@@ -65,6 +86,7 @@ pub(crate) fn check_rent_state(
     transaction_context: &TransactionContext,
     index: usize,
     include_account_index_in_err: bool,
+    restrict_rent_paying_accounts_ttl_extension: bool,
 ) -> Result<()> {
     if let Some((pre_rent_state, post_rent_state)) = pre_rent_state.zip(post_rent_state) {
         let expect_msg = "account must exist at TransactionContext index if rent-states are Some";
@@ -79,6 +101,7 @@ pub(crate) fn check_rent_state(
                 .expect(expect_msg)
                 .borrow(),
             include_account_index_in_err.then(|| index),
+            restrict_rent_paying_accounts_ttl_extension,
         )?;
     }
     Ok(())
@@ -90,10 +113,12 @@ pub(crate) fn check_rent_state_with_account(
     address: &Pubkey,
     account_state: &AccountSharedData,
     account_index: Option<usize>,
+    restrict_rent_paying_accounts_ttl_extension: bool,
 ) -> Result<()> {
     submit_rent_state_metrics(pre_rent_state, post_rent_state);
     if !solana_sdk::incinerator::check_id(address)
-        && !post_rent_state.transition_allowed_from(pre_rent_state)
+        && !post_rent_state
+            .transition_allowed_from(pre_rent_state, restrict_rent_paying_accounts_ttl_extension)
     {
         debug!(
             "Account {} not rent exempt, state {:?}",
@@ -152,7 +177,10 @@ mod tests {
         );
         assert_eq!(
             RentState::from_account(&rent_paying_account, &rent),
-            RentState::RentPaying(account_data_size)
+            RentState::RentPaying {
+                data_size: account_data_size,
+                lamports: rent_paying_account.lamports(),
+            }
         );
         assert_eq!(
             RentState::from_account(&rent_exempt_account, &rent),
@@ -162,21 +190,98 @@ mod tests {
 
     #[test]
     fn test_transition_allowed_from() {
+        check_transition_allowed_from(/*restrict_rent_paying_accounts_ttl_extension:*/ false);
+        check_transition_allowed_from(/*restrict_rent_paying_accounts_ttl_extension:*/ true);
+    }
+
+    fn check_transition_allowed_from(restrict_rent_paying_accounts_ttl_extension: bool) {
         let post_rent_state = RentState::Uninitialized;
-        assert!(post_rent_state.transition_allowed_from(&RentState::Uninitialized));
-        assert!(post_rent_state.transition_allowed_from(&RentState::RentExempt));
-        assert!(post_rent_state.transition_allowed_from(&RentState::RentPaying(0)));
+        assert!(post_rent_state.transition_allowed_from(
+            &RentState::Uninitialized,
+            restrict_rent_paying_accounts_ttl_extension
+        ));
+        assert!(post_rent_state.transition_allowed_from(
+            &RentState::RentExempt,
+            restrict_rent_paying_accounts_ttl_extension
+        ));
+        assert!(post_rent_state.transition_allowed_from(
+            &RentState::RentPaying {
+                data_size: 0,
+                lamports: 1,
+            },
+            restrict_rent_paying_accounts_ttl_extension
+        ));
 
         let post_rent_state = RentState::RentExempt;
-        assert!(post_rent_state.transition_allowed_from(&RentState::Uninitialized));
-        assert!(post_rent_state.transition_allowed_from(&RentState::RentExempt));
-        assert!(post_rent_state.transition_allowed_from(&RentState::RentPaying(0)));
-
-        let post_rent_state = RentState::RentPaying(2);
-        assert!(!post_rent_state.transition_allowed_from(&RentState::Uninitialized));
-        assert!(!post_rent_state.transition_allowed_from(&RentState::RentExempt));
-        assert!(!post_rent_state.transition_allowed_from(&RentState::RentPaying(3)));
-        assert!(!post_rent_state.transition_allowed_from(&RentState::RentPaying(1)));
-        assert!(post_rent_state.transition_allowed_from(&RentState::RentPaying(2)));
+        assert!(post_rent_state.transition_allowed_from(
+            &RentState::Uninitialized,
+            restrict_rent_paying_accounts_ttl_extension
+        ));
+        assert!(post_rent_state.transition_allowed_from(
+            &RentState::RentExempt,
+            restrict_rent_paying_accounts_ttl_extension
+        ));
+        assert!(post_rent_state.transition_allowed_from(
+            &RentState::RentPaying {
+                data_size: 0,
+                lamports: 1,
+            },
+            restrict_rent_paying_accounts_ttl_extension
+        ));
+        let post_rent_state = RentState::RentPaying {
+            data_size: 2,
+            lamports: 5,
+        };
+        assert!(!post_rent_state.transition_allowed_from(
+            &RentState::Uninitialized,
+            restrict_rent_paying_accounts_ttl_extension
+        ));
+        assert!(!post_rent_state.transition_allowed_from(
+            &RentState::RentExempt,
+            restrict_rent_paying_accounts_ttl_extension
+        ));
+        assert!(!post_rent_state.transition_allowed_from(
+            &RentState::RentPaying {
+                data_size: 3,
+                lamports: 5
+            },
+            restrict_rent_paying_accounts_ttl_extension
+        ));
+        assert!(!post_rent_state.transition_allowed_from(
+            &RentState::RentPaying {
+                data_size: 1,
+                lamports: 5
+            },
+            restrict_rent_paying_accounts_ttl_extension
+        ));
+        // No resize, same lamports is always allowed.
+        assert!(post_rent_state.transition_allowed_from(
+            &RentState::RentPaying {
+                data_size: 2,
+                lamports: 5
+            },
+            restrict_rent_paying_accounts_ttl_extension
+        ));
+        // No resize, fewer lamports is always allowed becasue that shortens
+        // rent paying account TTL.
+        assert!(post_rent_state.transition_allowed_from(
+            &RentState::RentPaying {
+                data_size: 2,
+                lamports: 7
+            },
+            restrict_rent_paying_accounts_ttl_extension
+        ));
+        // No resize, more lamports is not allowed once the feature is
+        // activated.
+        assert_eq!(
+            post_rent_state.transition_allowed_from(
+                &RentState::RentPaying {
+                    data_size: 2,
+                    lamports: 3
+                },
+                restrict_rent_paying_accounts_ttl_extension
+            ),
+            !restrict_rent_paying_accounts_ttl_extension
+        );
     }
 }

runtime/src/accounts.rs

@@ -441,6 +441,7 @@ impl Accounts {
             feature_set
                 .is_active(&feature_set::include_account_index_in_rent_error::ID)
                 .then(|| payer_index),
+            feature_set.is_active(&feature_set::restrict_rent_paying_accounts_ttl_extension::id()),
         )
     }
 

runtime/src/bank/transaction_account_state_info.rs

@@ -58,6 +58,9 @@ impl Bank {
         let include_account_index_in_err = self
             .feature_set
             .is_active(&feature_set::include_account_index_in_rent_error::id());
+        let restrict_rent_paying_accounts_ttl_extension = self
+            .feature_set
+            .is_active(&feature_set::restrict_rent_paying_accounts_ttl_extension::id());
         for (i, (pre_state_info, post_state_info)) in
             pre_state_infos.iter().zip(post_state_infos).enumerate()
         {
@@ -67,6 +70,7 @@ impl Bank {
                 transaction_context,
                 i,
                 include_account_index_in_err,
+                restrict_rent_paying_accounts_ttl_extension,
             )?;
         }
         Ok(())

sdk/src/feature_set.rs

@@ -456,6 +456,10 @@ pub mod enable_bpf_loader_extend_program_data_ix {
     solana_sdk::declare_id!("8Zs9W7D9MpSEtUWSQdGniZk2cNmV22y6FLJwCx53asme");
 }
 
+pub mod restrict_rent_paying_accounts_ttl_extension {
+    solana_sdk::declare_id!("812kqX67odAp5NFwM8D2N24cku7WTm9CHUTFUXaDkWPn");
+}
+
 lazy_static! {
     /// Map of feature identifiers to user-visible description
     pub static ref FEATURE_NAMES: HashMap<Pubkey, &'static str> = [
@@ -564,6 +568,7 @@ lazy_static! {
         (cap_accounts_data_size_per_block::id(), "cap the accounts data size per block #25517"),
         (preserve_rent_epoch_for_rent_exempt_accounts::id(), "preserve rent epoch for rent exempt accounts #26479"),
         (enable_bpf_loader_extend_program_data_ix::id(), "enable bpf upgradeable loader ExtendProgramData instruction #25234"),
+        (restrict_rent_paying_accounts_ttl_extension::id(), "restrict rent paying accounts TTL extension #26606"),
         /*************** ADD NEW FEATURES HERE ***************/
     ]
     .iter()