Can Other Programs Write to PDA Accounts even if the `Account` type is used and the ownership is checked?

Question

Question: Ownership and Write Permissions for PDA Accounts in Solana Programs

I’ve been exploring how the #[account] macro in the Anchor framework interacts with the ownership model of PDA accounts, particularly regarding write permissions. Here’s what I understand so far:

1. Ownership at Initialization:
   When a PDA (Program Derived Address) account A is initialized by a program p1, the owner field of the account is set to p1's program ID. This ownership ensures that p1 can use the Box<Account<'info, T>> wrapper for deserialization because it enforces the following ownership check:

   Account.info.owner == T::owner()
   

   Here, Account.info.owner is the runtime owner of the account, and T::owner() is the program ID derived from the #[account] macro, which is statically associated with p1.

2. Behavior of the #[account] Macro:
   The #[account] macro implements the Owner trait for the associated struct T using the program ID declared via declare_id!. This means the program ID of the struct’s defining program is embedded in the type, enabling the Account wrapper to verify ownership.

   From the documentation:

   "The #[account] attribute implements the Owner trait for a struct using the crate::ID declared by declare_id! in the same program."

3. Initialization and Discriminator Matching:
   During initialization, the PDA’s data includes a discriminator (the first 8 bytes) to identify the account type. This ensures that only p1, the initializing program, can create valid accounts of this type. Any program attempting to deserialize the account must satisfy the discriminator and ownership check.

   The combined condition is:

   Account.info.owner == T::owner()
   

4. Key Question: Can Other Programs Write to PDA Accounts? Why ??
   If the ownership (owner) of the PDA is set to p1, does this guarantee that only p1 can write to the account? Are there specific cases where another program could bypass this restriction, such as via cross-program invocation (CPI) with writable access or other mechanisms?

Follow-up Points:

• Is the combination of ownership (owner) and discriminator checks sufficient to ensure data integrity for the PDA account?
• How does this model compare to standard system accounts where ownership isn't explicitly checked for write permissions?

Any clarification or additional insights into these mechanisms would be highly appreciated!

Answer 1

Can other programs write to p1? No. Only the account owner has write permissions for Solana programs and can modify the data.

If you have a write_data instruction in your program p1 without any signer/ownership checks, then any program can call this instruction via CPI and write data to the account or anyone.

about the integrity of data, yes they are sufficient in ensuring the integrity of your data,

check out this answer about anchor discriminators and the section about the same in the anchor book

Standard accounts that have a public key and secret key are owned by the system program responsible for debiting the account imports, but the authority to do this is with the person who has access to the secret key.

ps. authority != ownership

accounts on Solana docs -> https://solana.com/docs/core/accounts