Re: [coLinux-users] change in slirp behavior from 0.7.1 to 0.7.3 with udp forwarded ports

[Mike F. <vap...@gm...>]

On Mon, Jun 23, 2008 at 4:27 PM, Henry Nestler wrote:
> With rev 479/480 you pointed to a bigger set of changes.
>
> By the while I found the place where it goes wrong. Please see the
> source snip or:
> http://colinux.svn.sourceforge.net/viewvc/colinux/branches/devel/src/colinux/user/slirp/udp.c?revision=677&view=markup
>
> file udp.c, line 323, function udp_output()
>
> In the line 323 the source address saddr.sin_addr (192.168.x.x) is
> overwritten with 10.0.2.2
> One line before was checked the listen address (so->so_faddr).
> I'm afraid, there should check the source address instead? But why there
> is a check for broadcast? Is that a hack for a hack? It sems me, that it
> would better work without the lines from 322 to 326 there?
>
> Background:
> special_addr = 10.0.2.2 (const)
>
> All UDP sockets are listen on address 0.0.0.0, that address is set as
> faked address 10.0.2.2 in line 383:
> "so->so_faddr = alias_addr;"
>
> -----------------------------------
> devel/src/colinux/user/slirp/udp.c
>  315 int udp_output(struct socket *so, struct mbuf *m,
>  316                struct sockaddr_in *addr)
>  317
>  318 {
>  319     struct sockaddr_in saddr, daddr;
>  320
>  321     saddr = *addr;
>  322     if ((so->so_faddr.s_addr & htonl(0xffffff00)) ==
> special_addr.s_addr) {
>  323         saddr.sin_addr.s_addr = so->so_faddr.s_addr;
>  324         if ((so->so_faddr.s_addr & htonl(0x000000ff)) == htonl(0xff))
>  325             saddr.sin_addr.s_addr = alias_addr.s_addr;
>  326     }
>  327     daddr.sin_addr = so->so_laddr;
>  328     daddr.sin_port = so->so_lport;
>  329
>  330     return udp_output2(so, m, &saddr, &daddr, so->so_iptos);
>  331 }

i'd like to assist in analysis, but i'm not familiar with any of the
colinux source base, so i cant really even make an educated guess; i'd
be shooting blind.  i'll gladly test any proposed changes though.

a comment block here in the source explaining what it's supposed to be
doing would have been useful :/.
-mike