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

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

On Thu, 13 Nov 2025 12:34:13 +1100 David Gibson 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

Applied.

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--- 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.

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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.

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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