pyth2wormhole: Fix a cfg migration bug, fix cfg lockout (see below) (#253)

This commit resolves a runtime problem in migrate() which occurred on devnet, as
well as invalid mutability for the old config and misuse of the
checked_sub() method.

The runtime problem came from a non-zero balance existing on
not-yet-used PDA. Effectively, this means permissionless
initialization of PDAs on Solana. Anyone can send lamports to any
account on Solana (existing or not), and it doesn't take much funds to
keep an empty account exempt. While it is possible to recover from it,
this case is relatively rare and takes a lot of code to
automate. Instead, we settle for a dumb bump of the config PDA
seed (see config.rs).

This measure is best used sparingly, as it imposes the same static
seed on all SOL networks. This will cause headaches if the attester
tooling grows a third-party user base.

Author: Stanisław Drozd

solana/pyth2wormhole/client/src/lib.rs

@@ -143,7 +143,7 @@ pub fn gen_migrate_tx(
 
     let accs = MigrateAccounts {
         new_config: Derived(p2w_addr),
-        old_config: DerivedRO(p2w_addr),
+        old_config: Derived(p2w_addr),
         current_owner: Signer(owner),
         payer: Signer(payer),
     };

solana/pyth2wormhole/program/src/config.rs

@@ -91,8 +91,13 @@ pub struct Pyth2WormholeConfigV2 {
     pub is_active: bool,
 }
 
+/// Note: If you get stuck with a pre-existing config account
+/// (e.g. someone transfers into a PDA that we're not using yet), it's
+/// usually easier to change the seed slightly
+/// (e.g. pyth2wormhole-config-v2 -> pyth2wormhole-config-v2.1). This
+/// saves a lot of time coding around this edge case.
 pub type P2WConfigAccountV2<'b, const IsInitialized: AccountState> =
-    Derive<Data<'b, Pyth2WormholeConfigV2, { IsInitialized }>, "pyth2wormhole-config-v2">;
+    Derive<Data<'b, Pyth2WormholeConfigV2, { IsInitialized }>, "pyth2wormhole-config-v2.1">;
 
 impl From<Pyth2WormholeConfigV1> for Pyth2WormholeConfigV2 {
     fn from(old: Pyth2WormholeConfigV1) -> Self {

solana/pyth2wormhole/program/src/migrate.rs

@@ -38,7 +38,7 @@ pub struct Migrate<'b> {
     /// New config account to be populated. Must be unused.
     pub new_config: Mut<P2WConfigAccount<'b, { AccountState::Uninitialized }>>,
     /// Old config using the previous format.
-    pub old_config: OldP2WConfigAccount<'b>,
+    pub old_config: Mut<OldP2WConfigAccount<'b>>,
     /// Current owner authority of the program
     pub current_owner: Mut<Signer<Info<'b>>>,
     /// Payer account for updating the account data
@@ -78,7 +78,7 @@ pub fn migrate(ctx: &ExecutionContext, accs: &mut Migrate, data: ()) -> SoliResu
     **accs.old_config.info().lamports.borrow_mut() = 0;
 
     // Credit payer with saved balance
-    accs.payer
+    let new_payer_balance = accs.payer
         .info()
         .lamports
         .borrow_mut()
@@ -88,5 +88,7 @@ pub fn migrate(ctx: &ExecutionContext, accs: &mut Migrate, data: ()) -> SoliResu
             SolitaireError::ProgramError(ProgramError::Custom(0xDEADBEEF))
         })?;
 
+    **accs.payer.info().lamports.borrow_mut() = new_payer_balance;
+
     Ok(())
 }