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

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

[David Gibson]

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>
---
 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.

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;
-- 
2.51.1

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

[Stefano Brivio]

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

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

[David Gibson]

[-- Attachment #1: Type: text/plain, Size: 1973 bytes --]

On Thu, Nov 13, 2025 at 11:22:23PM +0100, Stefano Brivio wrote:
> 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

Ah, missed that.

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

I guess we will.

> > 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
> 

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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