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From: Tom Pusateri <pusateri@bangj.com>
Subject: Re: UDP/IPv6 handling
Date: Wed, 1 Oct 2014 19:34:04 -0400
To: Michael Tuexen <Michael.Tuexen@lurchi.franken.de>
Cc: FreeBSD Net <freebsd-net@freebsd.org>
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Lots of embedded devices (like Cisco IP Phones) send TFTP requests with 0 ch=
ecksums.=20

Tom



> On Oct 1, 2014, at 12:58 PM, Michael Tuexen <Michael.Tuexen@lurchi.franken=
.de> wrote:
>=20
> Dear all,
>=20
> in udp6_input() we have the following code:
>=20
>    if (nxt =3D=3D IPPROTO_UDP && plen !=3D ulen) {
>        UDPSTAT_INC(udps_badlen);
>        goto badunlocked;
>    }=20
>    /*
>     * Checksum extended UDP header and data.
>     */
>    if (uh->uh_sum =3D=3D 0) {
>        if (ulen > plen || ulen < sizeof(struct udphdr)) {
>            UDPSTAT_INC(udps_nosum);
>            goto badunlocked;
>        }
>    }
>=20
> I'm trying to understand the UDP code path...
>=20
> So (ulen > plen) can't be true. I'm wondering why do we only check the ule=
n is not too
> short only in the case when the UDP checksum is zero. A zero checksum shou=
ld also never happen.
>=20
> I think we should check for ulen < sizeof(struct udphdr) in any case.
>=20
> Opinions?
>=20
> Best regards
> Michael
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