Can KEYCTL_SESSION_TO_PARENT be dropped entirely? -- was Re: [PATCH v2 1/2] KEYS: use synchronous task work for changing parent credentials

[Paul Moore]

On Thu, Aug 15, 2024 at 4:00 PM Jann Horn <jannh at google.com> wrote:
> On Thu, Aug 15, 2024 at 9:46 PM David Howells <dhowells at redhat.com> wrote:
> > Jann Horn <jannh at google.com> wrote:
> >
> > > Rewrite keyctl_session_to_parent() to run task work on the parent
> > > synchronously, so that any errors that happen in the task work can be
> > > plumbed back into the syscall return value in the child.
> >
> > The main thing I worry about is if there's a way to deadlock the child and the
> > parent against each other.  vfork() for example.
>
> Yes - I think it would work fine for scenarios like using
> KEYCTL_SESSION_TO_PARENT from a helper binary against the shell that
> launched the helper (which I think is the intended usecase?), but
> there could theoretically be constellations where it would cause an
> (interruptible) hang if the parent is stuck in
> uninterruptible/killable sleep.
>
> I think vfork() is rather special in that it does a killable wait for
> the child to exit or execute; and based on my understanding of the
> intended usecase of KEYCTL_SESSION_TO_PARENT, I think normally
> KEYCTL_SESSION_TO_PARENT would only be used by a child that has gone
> through execve?

Where did we land on all of this?  Unless I missed a thread somewhere,
it looks like the discussion trailed off without any resolution on if
we are okay with a potentially (interruptible) deadlock?

-- 
paul-moore.com