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

[Henry N. <hen...@ar...>]

Hello Mike,

Mike Frysinger wrote:
> On Sun, Jun 22, 2008 at 4:59 PM, Henry Nestler wrote:
>> The difference for coLinux 0.7.1 and 0.7.3 are very small. Mostly are
>> fixups for compiler warnings.
>>
>> There exist an other interesting change between versions:
>> http://colinux.svn.sourceforge.net/viewvc/colinux?view=rev&revision=574
> 
> so there may be a discrepancy when i said "0.7.1".  i was given an old
> coLinux installer and was told it was "0.7.1".  i assumed everything
> in the package was "0.7.1"; the person before me may have taken an
> older slirp daemon and dropped it in for this same reason.  so as to
> make things maintainable, i started fresh with the 0.7.3 release from
> colinux.org, hit this bug, and then copied the slirp daemon from this
> "0.7.1" version.
> 
> so let's just focus on the svn info i posted otherwise as that is used
> in conjunction with vanilla 0.7.3 install without any unknown baggage.
>  sorry for any confusion.
> -mike
> 

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 }

-- 
Henry N.