Date: Fri, 21 Jan 2000 19:19:59 -0700 From: Wes Peters <wes@softweyr.com> To: Poul-Henning Kamp <phk@critter.freebsd.dk> Cc: Matthew Dillon <dillon@apollo.backplane.com>, Alfred Perlstein <bright@wintelcom.net>, Brett Glass <brett@lariat.org>, security@freebsd.org Subject: Re: stream.c worst-case kernel paths Message-ID: <388913CF.DE7F4B0B@softweyr.com> References: <7192.948496931@critter.freebsd.dk>
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Poul-Henning Kamp wrote:
>
> In message <200001212311.PAA64559@apollo.backplane.com>, Matthew Dillon writes:
>
> > No, this is far too dangerous. If a packet is bad due to being
> > corrupted then you want to throw it away (via the checksum check)
> > *BEFORE* you start messing around with the socket state. Otherwise
> > a perfectly legitimate packet that got corrupted in transit may
> > cause a disconnect or other failure.
>
> It makes a lot of sense to do cheap (relative to the checksum)
> checks on the packet before we do the checksum, as long as we
> don't modify any state before the checksum is validated.
>
> If it is cheaper to try to locate the pcb, than to calculate the
> checksum, the locate the pcb first and drop the packet before
> doing the checksum.
Except you may get a false match on a garbled packet, that just happened
to get garbled to match a different connection. The checksum is done
first to avoid such situations. Until the packet has been verified good,
none of the data in it can be trusted.
--
"Where am I, and what am I doing in this handbasket?"
Wes Peters Softweyr LLC
wes@softweyr.com http://softweyr.com/
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