Re: MPPE in kernel?

[Frank Cusack <fcusack@fcusack.com>]

On Mon, May 12, 2003 at 11:07:20PM +1000, Paul Mackerras wrote:
> Frank Cusack writes:
> 
> > I have the compressor return a 3-valued return code (<0, 0, >0) instead of
> > two-valued (>0, other).  A negative value tells ppp_generic to drop the
> > packet.  0 means the same as it does now--the compressor failed for some
> > reason.  (All current compressors always return 0 or >0, so the negative
> > return is compatible.)
> > 
> > 0 could also mean that CCP isn't up yet, but pppd userland doesn't allow
> > NCP's to come up until CCP completes (iff trying to negotiate MPPE).
> 
> Hmmm, and are you sure that nothing can cause CCP to go down?  If it
> does then ppp_generic will send data uncompressed.  What would happen
> if an attacker managed to insert a CCP terminate-request into the
> receive stream somehow?

When (if) CCP goes down, pppd shuts down LCP if MPPE was running.  This
could move into the kernel if you think it's better that way, but I think
userland is ok.

static void
ccp_input(unit, p, len)
{
...
#ifdef MPPE
        if (ccp_gotoptions[unit].mppe) {
            error("MPPE disabled, closing LCP");
            lcp_close(unit, "MPPE disabled by peer");
        }
#endif
}

/fc