each commit's id is an integrity hash of the repository at the time of commit. git doesn't provide access control; it relies on access controls built-into which

each commit's id is an integrity hash of the repository at the time of commit. git doesn't provide access control; it relies on access controls built-into whichever transport mechanisms you choose to enable (https, ssh, etc). you can sign commits with PGP signatures and with hooks, you can reject commits that aren't signed. i believe maintainers sign commits in the linux repo.