[cap-talk] Confused Deputy, multiple authorities - Norm?

[David Wagner]

In article <200610251204590230.001880CC at smtp.village.it> you write:
>Can this problem be resolved by designing the "check+write" as an atomic
>operation ?

Yes.  That's exactly what the standard advice does.  You switch hats
to take on the appropriate userid, then go ahead and issue the write
request, and the OS will perform the check atomically before executing
the write operation.