[Qemu-devel] Re: [4267] Treat DNS a special case among special addresses in slirp ( Jason Wessel).

[Henry Nestler]

Hello Andrzej,

Andrzej Zaborowski wrote:
> Revision: 4267
>           http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=4267
> Author:   balrog
> Date:     2008-04-27 21:45:18 +0000 (Sun, 27 Apr 2008)
> 
> Log Message:
> -----------
> Treat DNS a special case among special addresses in slirp (Jason Wessel).
> 
> Modified Paths:
> --------------
>     trunk/slirp/udp.c
> 
> Modified: trunk/slirp/udp.c
> ===================================================================
> --- trunk/slirp/udp.c 2008-04-27 21:39:40 UTC (rev 4266)
> +++ trunk/slirp/udp.c 2008-04-27 21:45:18 UTC (rev 4267)
> @@ -318,11 +318,12 @@
>      struct sockaddr_in saddr, daddr;
>  
>      saddr = *addr;
> -    if ((so->so_faddr.s_addr & htonl(0xffffff00)) == special_addr.s_addr &&
> -        addr->sin_addr.s_addr == htonl(0x7f000001)) {
> -        saddr.sin_addr.s_addr = so->so_faddr.s_addr;
> +    if ((so->so_faddr.s_addr & htonl(0xffffff00)) == special_addr.s_addr) {
>          if ((so->so_faddr.s_addr & htonl(0x000000ff)) == htonl(0xff))
>              saddr.sin_addr.s_addr = alias_addr.s_addr;
> +        else if (addr->sin_addr.s_addr == loopback_addr.s_addr ||
> +                 ((so->so_faddr.s_addr & htonl(CTL_DNS)) == htonl(CTL_DNS)))
> +            saddr.sin_addr.s_addr = so->so_faddr.s_addr;
>      }
>      daddr.sin_addr = so->so_laddr;
>      daddr.sin_port = so->so_lport;

CoLinux found also a problem on this source lines.
We have fixed it more simple:

/* Check given address for localhost */
#define is_localhost(addr) \
        ((addr).s_addr == 0 || (addr).s_addr == loopback_addr.s_addr)
...
int udp_output(struct socket *so, struct mbuf *m,
               struct sockaddr_in *addr)

{
    struct sockaddr_in saddr, daddr;

    saddr = *addr;
    /* Translate connections from localhost to the alias hostname */
    if(is_localhost(saddr.sin_addr)) {
        saddr.sin_addr.s_addr = so->so_faddr.s_addr;
    }
    daddr.sin_addr = so->so_laddr;
    daddr.sin_port = so->so_lport;

    return udp_output2(so, m, &saddr, &daddr, so->so_iptos);
}


I can not say, how it would work in your environment. Remember: We have
changed the host address into localhost (127.0.0.1) and bind it on
0.0.0.0 all times. So we can simple replace all localhost or 0.0.0.0
with the faked address 10.0.2.2 as source.

http://colinux.svn.sourceforge.net/viewvc/colinux/branches/devel/src/colinux/user/slirp/udp.c
This is our repository. Currently the last change from this mail is not
commited. We need some more tests.

-- 
Henry N.