On Feb 1, 2010, at 6:27 AM, David Horn wrote:
> I have created a patch to support the RFC 5006 IPv6 RA option 25
> (RDNSS) decoding in tcpdump. The patch (against GIT) is available
> here:
>
> https://sourceforge.net/tracker/?func=detail&aid=2942379&group_id=53066&atid=469575
>
> I would appreciate a review of the code, as this is my first change to
> tcpdump.
There's no need for a "maximum DNS server addresses" value - the nd_opt_rdnss
structure doesn't have to cover all possible addresses, it can just have one,
and the printer can go past the nominal end of the structure.
Not all C compilers necessarily support declaration of variables in the middle
of a block:
oprd = (struct nd_opt_rdnss *)op;
int rdnss_len = oprd->nd_opt_rdnss_len;
so I just used the "l" variable, used elsewhere for option lengths - and set it
based on op->nd_opt_len, as is done with other options.
You just directly printed oprd->nd_opt_rdnss_lifetime, but it's a 4-byte value,
and
1) it's not guaranteed to be aligned on a 4-byte boundary, and not all
machines can dereference unaligned pointers without trapping;
2) it's not necessarily in the same byte order as the machine on which
you're running (in fact, these days there's an extremely good chance that it's
*not*, as most people running tcpdump are probably running it on a machine with
an x86 or x86-64 processor, and those are little-endian);
so it should be fetched with EXTRACT_32BITS().
It's probably best to print the addresses in order, rather than in reverse
order.
I've checked your patch in, with the changes in question.-
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