Re: Nmap/Nping bug on udp checksum calculation

[David Fifield <david () bamsoftware com>]

On Sun, Nov 03, 2013 at 06:49:19PM +0100, Luis MartinGarcia. wrote:
> Hi, David.
>
> Regarding this bug, I believe it also affects osscan2.cc. See below.
> What do you think?
>
>
> --- osscan2.cc    (revision 32492)
> +++ osscan2.cc    (working copy)
> @@ -2165,6 +2165,12 @@
>      /* OK, now we should be able to compute a valid checksum */
>      realcheck = ipv4_pseudoheader_cksum(source,
> hss->target->v4hostip(), IPPROTO_UDP,
>                                          sizeof(struct udp_hdr) +
> datalen, (char *) udp);
> +
> +    /* If the computed checksum has a value of zero, we need to set it
> +     * to 0xFFFF (See RFC 768) */
> +    if(realcheck==0)
> +      realcheck=0xFFFF;
> +   
>  #if STUPID_SOLARIS_CHECKSUM_BUG
>      udp->uh_sum = sizeof(struct udp_hdr) + datalen;
>  #else

Good catch. I agree with you.

David Fifield
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