Date: Wed, 1 Oct 2014 22:51:06 -0500 From: Bryan Venteicher <bryanv@daemoninthecloset.org> To: Michael Tuexen <Michael.Tuexen@lurchi.franken.de> Cc: FreeBSD Net <freebsd-net@freebsd.org> Subject: Re: UDP/IPv6 handling Message-ID: <CAMo0n6Q56yvHYp8XUG499gkkxL0=QRdTVDvph9jA=kNL4%2BS-1A@mail.gmail.com> In-Reply-To: <B30E0A41-51B0-442C-9476-0D9E99C0D37C@lurchi.franken.de> References: <B30E0A41-51B0-442C-9476-0D9E99C0D37C@lurchi.franken.de>
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On Wed, Oct 1, 2014 at 11:58 AM, Michael Tuexen <
Michael.Tuexen@lurchi.franken.de> wrote:
> Dear all,
>
> in udp6_input() we have the following code:
>
> if (nxt == IPPROTO_UDP && plen != ulen) {
> UDPSTAT_INC(udps_badlen);
> goto badunlocked;
> }
> /*
> * Checksum extended UDP header and data.
> */
> if (uh->uh_sum == 0) {
> if (ulen > plen || ulen < sizeof(struct udphdr)) {
> UDPSTAT_INC(udps_nosum);
> goto badunlocked;
> }
> }
>
> I'm trying to understand the UDP code path...
>
>
​I too was recently confused by this code. ​I pointed out one issue to
kevlo@ recently, but it still kind of seemed like the UDP-Lite was
mismerged to IPv6.
So (ulen > plen) can't be true. I'm wondering why do we only check the ulen
> is not too
> short only in the case when the UDP checksum is zero. A zero checksum
> should also never happen.
>
>
​I hope to have a patch for ​RFC6935 [1] soon so a zero checksum may be
allowed if the inp/udpcb is configured for it.
I think we should check for ulen < sizeof(struct udphdr) in any case.
>
>
​I think previously, the checks in ip6_input(), IP6_EXTHDR_CHECK(), and
plen == ulen made this unnecessary. I think we'd want to do it for UDP-Lite
if ulen was not initially zero.
​[1] - http://tools.ietf.org/html/rfc6935​
> Opinions?
>
> Best regards
> Michael
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