Can't bind ipv4-mapped ipv6 address

[Aaron LI]

Hi Aleksej,

DragonFly doesn’t support the ‘IPV6_V6ONLY’ socket option, and thus no support of IPv4-mapped IPv6 address.

So a dual-stack program must create one IPv4 socket *and* another IPv6 socket.

See also the ip6(4) man page:
https://man.dragonflybsd.org/?command=ip6&section=ANY

— 
Aaron

> On Feb 22, 2023, at 06:10, Aleksej Lebedev <root at zta.lk> wrote:
> 
> Hi,
> 
> I think I found a bug in bind(2) or at least the behavior that differs from Linux and is expected to like in Linux.
> On linux instead of creating a PF_INET UDP socket and assigning an ipv4 address I can create PF_INET6 UDP socket and assigning it an ipv4-mapped ipv6 address (i.e. ::ffff:x.x.x.x).
> On DragonFly the first way works (of course) but the second option doesn't seem to:
> 
> $ cat test_bind.c 
> #include <stdio.h>
> #include <stdlib.h>
> #include <netinet/in.h>
> #include <sys/types.h>
> #include <sys/socket.h>
> #include <arpa/inet.h>
> 
> void die(const char *s) { perror(s); exit(1); }
> 
> int main()
> {
>  struct sockaddr_in sa;
>  int s, r;
> 
>  s = socket(PF_INET, SOCK_DGRAM, 0);
> 
>  r = inet_pton(AF_INET, "176.9.104.141", &sa.sin_addr);
>  if (r == INADDR_NONE) die("inet_pton");
> 
>  sa.sin_family = AF_INET;
>  sa.sin_port = 53;
> 
>  r = bind(s, (const struct sockaddr *)&sa, sizeof sa);
>  if (r != 0) die("bind");
> 
> }
> $ cc test_bind.c && a.out
> $ echo $?
> 0
> 
> $ cat test_bind6.c 
> #include <stdio.h>
> #include <stdlib.h>
> #include <netinet/in.h>
> #include <sys/types.h>
> #include <sys/socket.h>
> #include <arpa/inet.h>
> 
> void die(const char *s) { perror(s); exit(1); }
> 
> int main()
> {
>  struct sockaddr_in6 sa;
>  int s, r;
> 
>  s = socket(PF_INET6, SOCK_DGRAM, 0);
> 
>  r = inet_pton(AF_INET6, "::ffff:176.9.104.141", &sa.sin6_addr);
>  if (r == INADDR_NONE) die("inet_pton");
> 
>  sa.sin6_family = AF_INET6;
>  sa.sin6_port = 53;
> 
>  r = bind(s, (const struct sockaddr *)&sa, sizeof sa);
>  if (r != 0) die("bind");
> 
> }
> $ cc test_bind6.c && ./a.out
> bind: Can't assign requested address
> $ echo $?
> 1
> 
> On Linux both versions work.
> 
> --
> Aleksej Lebedev
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