Обсуждение: Re: [PATCH] Why is_admin_of_role() uses ROLERECURSE_MEMBERS rather than ROLERECURSE_PRIVS?
> create user u1;
> create user u2;
> create user u3;
> create user u4;
> grant u2 to u1 with admin true ;
> grant u3 to u2 with admin true ;
> revoke inherit option for u2 from u1 ;
> set session authorization u1;
> grant u3 to u4;
PostgreSQL calls select_best_admin() internally. If that function returns InvalidOid, I think it means that “The system tried all the possible grantor roles (roles we belong to that have ADMIN OPTION), but none are currently usable.” i.e the system couldn’t find a grantor role in the current context, so it reports: "no possible grantors"
>The "grant u3 to u4;" will report error "no possible grantors" rather than "permission denied to grant role".
> Is this the expected behavior
Again I think a “permission denied” would imply we tried as a specific role, and that role doesn’t have permission. But here, Postgres never even found which role we could be acting as. So from the system’s logic, it’s not a denied action; it’s “no valid takers found to even attempt the action.”
> but the "no possible grantors" error can happen in my test case.
> The main reason is that is_admin_of_role() and select_best_admin() use different role recurse methods.
> I think they should keep consistent, maybe both use ROLERECURSE_PRIVS? Thoughts?
I think ROLERECURSE_MEMBERS traverses membership relationships among roles regardless of whether inheritance or session activation is in play, while ROLERECURSE_PRIVS recursively traverses active privileges. and only consider roles whose privileges are currently usable i.e. those with inherit still true, or roles that are currently SET ROLE’d into.
I believe is_admin_of_role() uses ROLERECURSE_MEMBERS because is_admin_of_role() is not used for permission enforcement and Its purpose is to answer checks like “does A have the ADMIN OPTION for B (anywhere in the membership graph)?” So it needs to see all possible relationships, even if the intermediate memberships are non-inheriting or currently inactive.
If A was once granted B WITH ADMIN OPTION, then regardless of INHERIT, A is “an admin of B” from the system’s metadata perspective. Therefore, it recurses through memberships unconditionally while ignoring session state.
select_best_admin() is called at execution time when we actually run a GRANT or REVOKE command. At that moment, PostgreSQL must know: “Given the roles the current user is effectively using right now, which one is a valid grantor?”. Hence it can only follow active, usable privileges i.e. it uses ROLERECURSE_PRIVS.
Regards,
Pretham
Hi, Thank you for your reply. > PostgreSQL calls select_best_admin() internally. If that function returns > InvalidOid, I think it means that “The system tried all the possible > grantor roles (roles we belong to that have ADMIN OPTION), but none are > currently usable.” i.e the system couldn’t find a grantor role in the > current context, so it reports: "no possible grantors" +1 > Again I think a “permission denied” would imply we tried as a specific > role, and that role doesn’t have permission. But here, Postgres never even > found which role we could be acting as. So from the system’s logic, it’s > not a denied action; it’s “no valid takers found to even attempt the > action.” Due to the "revoke inherit option for u2 from u1", I think reporting "permission denied ..." here is reasonable. The "no possible grantors" is more like an internal error, and should not be reported to users. > I believe is_admin_of_role() uses ROLERECURSE_MEMBERS because > is_admin_of_role() is not used for permission enforcement and Its purpose > is to answer checks like “does A have the ADMIN OPTION for B (anywhere in > the membership graph)?” So it needs to see all possible relationships, even > if the intermediate memberships are non-inheriting or currently inactive. But many places report "permission denied ..." if is_admin_of_role() return false. -- Regards, ChangAo Chen