On Mon, Jan 13, 2020 at 11:27:03AM -0800, Daniel Colascione wrote: > On Mon, Jan 13, 2020 at 11:10 AM Christian Brauner > <christian.brauner@xxxxxxxxxx> wrote: > > This does not > > affect the permission checking you're performing here. > > Pidfds-as-capabilities sounds like a good change. Can you clarify what > you mean here though? Do you mean that in order to perform some > process-directed operation X on process Y, the pidfd passed to X must > have been opened with PIDFD_CAP_X *and* the process *using* the pidfds > must be able to perform operation X on process Y? Or do pidfds in this > model "carry" permissions in the same way that an ordinary file > descriptor "carries" the ability to write to a file if it was opened > with O_WRONLY even if the FD is passed to a process that couldn't > otherwise write to that file? Right now, pidfds are identity-only and > always rely on the caller's permissions. I like the capability bit > model because it makes pidfds more consistent with other file > descriptors and enabled delegation of capabilities across the system. I'm going back and forth on this. My initial implementation has it that you'd need both, PIDFD_FLAG/CAP_X and the process using the pidfd must be able to perform the operation X on process Y. The alternative becomes tricky for e.g. anything that requires ptrace_may_access() permissions such as getting an fd out from another task based on its pidfd and so on. Christian
