On 02 Oct 2014, at 01:34, Tom Pusateri <pusat...@bangj.com> wrote:
> Lots of embedded devices (like Cisco IP Phones) send TFTP requests with 0
> checksums.
I guess this uses UDP/IPv4, where FreeBSD supports UDP with zero checksum.
For UDP/IPv6 this doesn't work. Right after the cited code, the checksum is
always
checked...
Best regards
Michael
>
> Tom
>
>
>
>> On Oct 1, 2014, at 12:58 PM, Michael Tuexen
>> <michael.tue...@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...
>>
>> 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 think we should check for ulen < sizeof(struct udphdr) in any case.
>>
>> Opinions?
>>
>> Best regards
>> Michael
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