RE: On PATH_MAX

[Jonathan S. Shapiro]

On Mon, 2005-11-07 at 09:32 -0700, Christopher Nelson wrote:
> Now, imagine that Thread A prepares a service request plus data for
> Thread B.  Imagine that this request is deliberately crafted to involve
> all available address space.  Thread A delivers the request to Thread B.
> In order for Thread B to even *consider* the request, it must map the
> memory into it's own address space.

In order to map the data, thread B must know the size of the payload,
and can therefore determine that the mapping violates the contract.

>   Now, let us say that Thread C needs
> to communicate with Thread B as well.

This assumes that thread B is obligated to *retain* an excessively large
mapping after the end of its interaction with thread A. Once A has
violated the contract, I would say that thread B is very much within its
rights to terminate the session with A, decommit all state held on
behalf of A, and ummap A's data.

It is possible to design protocols that are flawed in the way that you
describe, but they are self-evidently broken.


shap