cross_program_invocation.md

CROSS PROGRAM INVOCATION:

The "arbitrary cross-program invocation issue" refers to the potential risks associated with allowing one program to invoke methods of another program without proper validation and safeguards. If not handled carefully, this can lead to unintended consequences or vulnerabilities in the system.

Suppose you have two Solana programs, Program A and Program B, each defined using Solana Anchor. Program A has a method initialize_account that sets up an account's initial state. Program B has a method update_balance that modifies the balance of an account.

Program A:

#[program]
mod program_a {
    use anchor_lang::prelude::*;

    #[state]
    pub struct MyState {
        pub initialized: bool,
    }

    impl<'info> From<&mut Context<'info>> for MyState {
        fn from(_c: &mut Context) -> Self {
            MyState {
                initialized: false,
            }
        }
    }

    #[derive(Accounts)]
    pub struct InitializeAccount<'info> {
        #[account(init)]
        pub my_account: ProgramAccount<'info, MyState>,
        pub system_program: Program<'info, System>,
    }

    #[access_control(InitializeAccount::accounts(&self, &ctx, accounts))]
    pub fn initialize_account(ctx: Context<InitializeAccount>) -> ProgramResult {
        ctx.accounts.my_account.initialized = true;
        Ok(())
    }
}

Program B:

#[program]
mod program_b {
    use anchor_lang::prelude::*;

    #[derive(Accounts)]
    pub struct UpdateBalance<'info> {
        #[account(mut)]
        pub my_account: ProgramAccount<'info, MyState>,
    }

    pub fn update_balance(ctx: Context<UpdateBalance>, new_balance: u64) -> ProgramResult {
        ctx.accounts.my_account.balance = new_balance;
        Ok(())
    }
}

Now, imagine that Program A invokes the update_balance method of Program B without proper validation or access control. This could lead to an arbitrary cross-program invocation issue, where Program A is modifying the state of Program B without proper authorization.

When one Solana Anchor program calls a method from another Solana Anchor program, it's typically done in a structured and controlled manner using the Accounts and With attributes provided by Anchor.

Here's how it works:

1. Define Invoked Method's Parameters: The program that needs to invoke another program's method defines a struct with attributes from the target program's method. This struct usually includes accounts that the target method requires as parameters.

2. Construct Accounts: The invoking program constructs the necessary accounts using the Accounts attribute. These accounts represent the accounts required by the target method. It's important to ensure that these accounts are properly authorized and structured according to the target program's expectations.

3. Invoke the Method: The invoking program can then call the target program's method using the invoke function provided by Anchor. This function takes the method's identifier, the constructed accounts, and any additional arguments.

4. Execute the Transaction: The invoking program includes the method invocation as part of a Solana transaction and signs it with appropriate signatures.

Here's a simplified example:

Suppose we have two Solana Anchor programs, Program A and Program B. Program A wants to invoke a method from Program B.

// Program A
#[program]
mod program_a {
    // ... imports and state

    #[derive(Accounts)]
    pub struct CallProgramB<'info> {
        #[account(mut)]
        pub program_b_account: AccountInfo<'info>,
        // ... other accounts required by Program B's method
    }

    pub fn call_program_b(ctx: Context<CallProgramB>) -> ProgramResult {
        // Construct accounts for Program B's method
        let program_b_accounts = vec![ctx.accounts.program_b_account.clone()];

        // Invoke Program B's method
        anchor_lang::sol_invoke_signed(
            &program_b_accounts,
            &[
                ctx.accounts.program_b_account.clone(),
                // ... other accounts
            ],
            &[
                // ... instructions
            ],
        );

        // ... perform other actions

        Ok(())
    }
}

In this example, program_a constructs an account for Program B and invokes its method using sol_invoke_signed.

To avoid this issue, proper access control checks and validations should be implemented in both programs to ensure that only authorized programs can invoke specific methods and access relevant data.

It's important to carefully design and implement cross-program invocations to avoid unintended security vulnerabilities and ensure the integrity of the Solana blockchain ecosystem.