Re: [PATCH] udp: Use IP_FREEBIND for flow sockets as well as listening sockets

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 13 Nov 2025 12:34:13 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> The --freebind option allows pasta to listen on addresses that aren't
> registered on the host, which has a number of use cases.  However, we
> omitted this option for UDP "flow sockets" which are created once a flow
> is started, connect()ed specifically to the peer.  Flow sockets are also
> bound, and if the peer has contacted a freebind address, we need
> IP_FREEBIND to do so.
> 
> Link: https://bugs.passt.top/show_bug.cgi?id=174
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Applied.

> ---
>  util.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> I'm still waiting on confirmation from the reporter that this actually
> fixes bug 174.  However, I'm pretty sure this is _a_ correct fix,
> whether or not it's a complete fix for the issue seen by the reporter.

From https://bugs.passt.top/show_bug.cgi?id=174#c0:

  I can't downgrade passt/pasta to an earlier version or test patches in
  my current setup

...so I guess we'll have to guess...

> diff --git a/util.c b/util.c
> index 44c21a3e..ab23463b 100644
> --- a/util.c
> +++ b/util.c
> @@ -67,9 +67,8 @@ int sock_l4_sa(const struct ctx *c, enum epoll_type type,
>  		freebind = c->freebind;
>  		break;
>  	case EPOLL_TYPE_UDP_LISTEN:
> -		freebind = c->freebind;
> -		/* fallthrough */
>  	case EPOLL_TYPE_UDP:
> +		freebind = c->freebind;
>  		proto = IPPROTO_UDP;
>  		socktype = SOCK_DGRAM | SOCK_NONBLOCK;
>  		break;

-- 
Stefano