Re: [PATCH 2/2] conf, icmp, tcp, udp: Add options to bind to outbound address and interface

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 9 Mar 2023 09:02:57 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Wed, Mar 08, 2023 at 08:34:49AM +0100, Stefano Brivio wrote:
> > I didn't notice earlier: libslirp (and slirp4netns) supports binding
> > outbound sockets to specific IPv4 and IPv6 addresses, to force the
> > source addresse selection. If we want to claim feature parity, we
> > should implement that as well.
> > 
> > Further, Podman supports specifying outbound interfaces as well, but
> > this is simply done by resolving the primary address for an interface
> > when the network back-end is started. However, since kernel version
> > 5.7, commit c427bfec18f2 ("net: core: enable SO_BINDTODEVICE for
> > non-root users"), we can actually bind to a specific interface name,
> > which doesn't need to be validated in advance.
> > 
> > Implement -o / --outbound ADDR to bind to IPv4 and IPv6 addresses,
> > and --outbound-ip4 and --outbound-ip6 to bind IPv4 and IPv6 sockets
> > to given interfaces.  
> 
> You have 'outbound-ip' here but 'outbound-if' in the code, I think you
> intended the latter.

Oops, right.

> > For ICMP and UDP, we call sock_l4() to open outbound sockets, as we
> > already needed to bind to given ports or echo identifiers, and we
> > can bind() a socket only once: there, pass address (if any) and
> > interface (if any) for the existing bind() and setsockopt() calls.
> > 
> > For TCP, in general, we wouldn't otherwise bind sockets. Add a
> > specific helper to do that.
> > 
> > For UDP outbound sockets, we need to know if the final destination
> > of the socket is a loopback address, before we decide whether it
> > makes sense to bind the socket at all: move the block mangling the
> > address destination before the creation of the socket in the IPv4
> > path. This was already the case for the IPv6 path.
> > 
> > Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
> > ---
> >  conf.c  | 78 +++++++++++++++++++++++++++++++++++++++++++++++++++++----
> >  icmp.c  | 24 +++++++++++++++---
> >  passt.1 | 19 ++++++++++++++
> >  passt.h | 10 ++++++++
> >  tcp.c   | 60 ++++++++++++++++++++++++++++++++++++++++++++
> >  udp.c   | 54 ++++++++++++++++++++++++++-------------
> >  6 files changed, 219 insertions(+), 26 deletions(-)
> > 
> > diff --git a/conf.c b/conf.c
> > index 3aa3314..15506ec 100644
> > --- a/conf.c
> > +++ b/conf.c
> > @@ -776,6 +776,13 @@ static void usage(const char *name)
> >  	info(   "    default: gateway from interface with default route");
> >  	info(   "  -i, --interface NAME	Interface for addresses and routes");
> >  	info(   "    default: interface with first default route");  
> 
> So, I think the outbound IP and the IP we advertise to the guest
> should be the same.  Certainly by default, and I'm not sure I can even
> think of any case where it would be useful for them to be different.
> That fits with the "only NAT when we really have to" goal.

Sure, that's a goal, but users might want to do NAT for whatever
reason, even just for slirp4netns compatibility (which we should
*really* support to play along nicely with Podman).

At the moment, it's already enough to pass '-a 10.200.0.2' and the
outbound address will be (in general) different from what we advertise.

> So, could we just add say, --if4 and --if6 instead of having explicit
> --outbound-* options?  -i X would be equivalent to "--if4 X --if6 X".
> 
> > +	info(   "  -o, --outbound ADDR	Bind to address as outbound source");
> > +	info(   "    can be specified zero to two times (for IPv4 and IPv6)");
> > +	info(   "    default: use source address from routing tables");  
> 
> On the same reasoning, can we merge this option with '-a' setting both
> outbound and assigned address by default?

Well, but this would effectively disable any possibility to do NAT: if
you want to assign a different address, it needs to be available on the
host too.

> Even if we want to allow setting these differently for some strange
> cases, I think the more obvious primary "address" and "interface"
> options should set the outbound address/interface.  The DHCP
> advertised address should match that unless we use some more obscure
> option to override it.

What do you do if that address is not available on the host, though?

Also mind that this option (which I'd like to add mostly for
slirp4netns feature parity) seems to have been introduced in libslirp
to enable the selection of a particular address on an interface with
multiple addresses -- so --if4/--if6 wouldn't be enough for that.

We could have -a selecting the outbound address, but then users can't
do NAT with it.

We could skip the --outbound-if4 and --outbound-if6 parts, but they
have the advantage (over bind()) that the interface doesn't actually
need to exist when we start.

There's also the advantage that the user doesn't need to fetch a given
address (which might even change later) if all they want is controlling
the outbound path, without affecting the source address.

Those options (--outbound-if4 and --outbound-if6) have no equivalent in
libslirp, and Podman approximates them by picking an address from the
given interface just before slirp4netns starts, so strictly speaking
this is not needed for slirp4netns compatibility, but I thought it's a
more "correct" way to implement that.

> In fact... thinking further on that, I'm not convinced there's any
> real use for a "template" interface.  Normally it should match the
> outbound interface - and if you want it different, I don't think it
> really buys anything over explicitly overriding the DHCP advertised
> address etc.

Normally, yes, but if you want it different, what you propose also
imposes some serious limitations.

> > +	info(   "  --outbound-if4 NAME	Bind to outbound interface for IPv4");
> > +	info(   "    default: use interface from default route");
> > +	info(   "  --outbound-if6 NAME	Bind to outbound interface for IPv6");
> > +	info(   "    default: use interface from default route");
> >  	info(   "  -D, --dns ADDR	Use IPv4 or IPv6 address as DNS");
> >  	info(   "    can be specified multiple times");
> >  	info(   "    a single, empty option disables DNS information");
> > @@ -900,7 +907,7 @@ pasta_opts:
> >   */
> >  static void conf_print(const struct ctx *c)
> >  {
> > -	char buf4[INET_ADDRSTRLEN], ifn[IFNAMSIZ];
> > +	char buf4[INET_ADDRSTRLEN], buf6[INET6_ADDRSTRLEN], ifn[IFNAMSIZ];
> >  	int i;
> >  
> >  	info("Template interface: %s%s%s%s%s",
> > @@ -910,6 +917,26 @@ static void conf_print(const struct ctx *c)
> >  	     c->ifi6 ? if_indextoname(c->ifi6, ifn) : "",
> >  	     c->ifi6 ? " (IPv6)" : "");
> >  
> > +	if (*c->ip4.ifname_out || *c->ip6.ifname_out) {
> > +		info("Outbound interface: %s%s%s%s%s",
> > +		     *c->ip4.ifname_out ? c->ip4.ifname_out : "",
> > +		     *c->ip4.ifname_out ? " (IPv4)" : "",
> > +		     (*c->ip4.ifname_out && *c->ip6.ifname_out) ? ", " : "",
> > +		     *c->ip6.ifname_out ? c->ip6.ifname_out : "",
> > +		     *c->ip6.ifname_out ? " (IPv6)" : "");
> > +	}
> > +
> > +	if (!IN4_IS_ADDR_UNSPECIFIED(&c->ip4.addr_out) ||
> > +	    !IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr_out)) {
> > +		info("Outbound address: %s%s%s",
> > +		     IN4_IS_ADDR_UNSPECIFIED(&c->ip4.addr_out) ? "" :
> > +		     inet_ntop(AF_INET, &c->ip4.addr_out, buf4, sizeof(buf4)),
> > +		     (!IN4_IS_ADDR_UNSPECIFIED(&c->ip4.addr_out) &&
> > +		      !IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr_out)) ? ", " : "",
> > +		     IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr_out) ? "" :
> > +		     inet_ntop(AF_INET6, &c->ip6.addr_out, buf6, sizeof(buf6)));
> > +	}
> > +
> >  	if (c->mode == MODE_PASTA)
> >  		info("Namespace interface: %s", c->pasta_ifn);
> >  
> > @@ -948,8 +975,6 @@ static void conf_print(const struct ctx *c)
> >  	}
> >  
> >  	if (c->ifi6) {
> > -		char buf6[INET6_ADDRSTRLEN];
> > -
> >  		if (!c->no_ndp && !c->no_dhcpv6)
> >  			info("NDP/DHCPv6:");
> >  		else if (!c->no_ndp)
> > @@ -1125,6 +1150,7 @@ void conf(struct ctx *c, int argc, char **argv)
> >  		{"mac-addr",	required_argument,	NULL,		'M' },
> >  		{"gateway",	required_argument,	NULL,		'g' },
> >  		{"interface",	required_argument,	NULL,		'i' },
> > +		{"outbound",	required_argument,	NULL,		'o' },
> >  		{"dns",		required_argument,	NULL,		'D' },
> >  		{"search",	required_argument,	NULL,		'S' },
> >  		{"no-tcp",	no_argument,		&c->no_tcp,	1 },
> > @@ -1157,6 +1183,8 @@ void conf(struct ctx *c, int argc, char **argv)
> >  		{"runas",	required_argument,	NULL,		12 },
> >  		{"log-size",	required_argument,	NULL,		13 },
> >  		{"version",	no_argument,		NULL,		14 },
> > +		{"outbound-if4", required_argument,	NULL,		15 },
> > +		{"outbound-if6", required_argument,	NULL,		16 },
> >  		{ 0 },
> >  	};
> >  	struct get_bound_ports_ns_arg ns_ports_arg = { .c = c };
> > @@ -1175,9 +1203,9 @@ void conf(struct ctx *c, int argc, char **argv)
> >  
> >  	if (c->mode == MODE_PASTA) {
> >  		c->no_dhcp_dns = c->no_dhcp_dns_search = 1;
> > -		optstring = "dqfel:hF:I:p:P:m:a:n:M:g:i:D:S:46t:u:T:U:";
> > +		optstring = "dqfel:hF:I:p:P:m:a:n:M:g:i:o:D:S:46t:u:T:U:";
> >  	} else {
> > -		optstring = "dqfel:hs:F:p:P:m:a:n:M:g:i:D:S:461t:u:";
> > +		optstring = "dqfel:hs:F:p:P:m:a:n:M:g:i:o:D:S:461t:u:";
> >  	}
> >  
> >  	c->tcp.fwd_in.mode = c->tcp.fwd_out.mode = 0;
> > @@ -1295,6 +1323,26 @@ void conf(struct ctx *c, int argc, char **argv)
> >  				c->mode == MODE_PASST ? "passt " : "pasta ");
> >  			fprintf(stdout, VERSION_BLOB);
> >  			exit(EXIT_SUCCESS);
> > +		case 15:
> > +			if (*c->ip4.ifname_out)
> > +				die("Redundant outbound interface: %s", optarg);
> > +
> > +			ret = snprintf(c->ip4.ifname_out,
> > +				       sizeof(c->ip4.ifname_out), "%s", optarg);
> > +			if (ret <= 0 || ret >= (int)sizeof(c->ip4.ifname_out))
> > +				die("Invalid interface name: %s", optarg);
> > +
> > +			break;
> > +		case 16:
> > +			if (*c->ip6.ifname_out)
> > +				die("Redundant outbound interface: %s", optarg);
> > +
> > +			ret = snprintf(c->ip6.ifname_out,
> > +				       sizeof(c->ip6.ifname_out), "%s", optarg);
> > +			if (ret <= 0 || ret >= (int)sizeof(c->ip6.ifname_out))
> > +				die("Invalid interface name: %s", optarg);
> > +
> > +			break;
> >  		case 'd':
> >  			if (c->debug)
> >  				die("Multiple --debug options given");
> > @@ -1466,6 +1514,26 @@ void conf(struct ctx *c, int argc, char **argv)
> >  				die("Invalid interface name %s: %s", optarg,
> >  				    strerror(errno));
> >  			break;
> > +		case 'o':
> > +			if (IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr_out)	  &&
> > +			    inet_pton(AF_INET6, optarg, &c->ip6.addr_out) &&
> > +			    !IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr_out)	  &&
> > +			    !IN6_IS_ADDR_LOOPBACK(&c->ip6.addr_out)	  &&
> > +			    !IN6_IS_ADDR_V4MAPPED(&c->ip6.addr_out)	  &&
> > +			    !IN6_IS_ADDR_V4COMPAT(&c->ip6.addr_out)	  &&
> > +			    !IN6_IS_ADDR_MULTICAST(&c->ip6.addr_out))
> > +				break;
> > +
> > +			if (IN4_IS_ADDR_UNSPECIFIED(&c->ip4.addr_out)	 &&
> > +			    inet_pton(AF_INET, optarg, &c->ip4.addr_out) &&
> > +			    !IN4_IS_ADDR_UNSPECIFIED(&c->ip4.addr_out)	 &&
> > +			    !IN4_IS_ADDR_BROADCAST(&c->ip4.addr_out)	 &&
> > +			    !IN4_IS_ADDR_MULTICAST(&c->ip4.addr_out))
> > +				break;
> > +
> > +			die("Invalid or redundant outbound address: %s",
> > +			    optarg);
> > +			break;  
> 
> I haven't really looked at any of the conf stuff above, since it will
> change if we alter the option semantics as I've suggested.
> 
> >  		case 'D':
> >  			if (!strcmp(optarg, "none")) {
> >  				if (c->no_dns)
> > diff --git a/icmp.c b/icmp.c
> > index b842fa8..ddf83f8 100644
> > --- a/icmp.c
> > +++ b/icmp.c
> > @@ -170,8 +170,16 @@ int icmp_tap_handler(const struct ctx *c, int af, const void *addr,
> >  		iref.icmp.id = id = ntohs(ih->un.echo.id);
> >  
> >  		if ((s = icmp_id_map[V4][id].sock) <= 0) {
> > -			s = sock_l4(c, AF_INET, IPPROTO_ICMP, NULL, NULL, id,
> > -				    iref.u32);
> > +			const struct in_addr *bind_addr = NULL;
> > +			const char *bind_if;
> > +
> > +			bind_if = *c->ip4.ifname_out ? c->ip4.ifname_out : NULL;
> > +
> > +			if (!IN4_IS_ADDR_UNSPECIFIED(&c->ip4.addr_out))
> > +				bind_addr = &c->ip4.addr_out;
> > +
> > +			s = sock_l4(c, AF_INET, IPPROTO_ICMP, bind_addr,
> > +				    bind_if, id, iref.u32);  
> 
> LGTM, modulo field names - again I think we should position "outbound
> address" as simply "the address", with "DHCP advertised address" as
> the special case override.

But from passt/pasta's perspective, "the address" is already what's
expected to be used by the guest/container. We use that all over the
place, and I think it might really need to be different from an address
we "externally" bind to.

I really wouldn't like to see users coming up with netfilter-based hacks
to support this. :/

> >  			if (s < 0)
> >  				goto fail_sock;
> >  			if (s > SOCKET_MAX) {
> > @@ -216,8 +224,16 @@ int icmp_tap_handler(const struct ctx *c, int af, const void *addr,
> >  
> >  		iref.icmp.id = id = ntohs(ih->icmp6_identifier);
> >  		if ((s = icmp_id_map[V6][id].sock) <= 0) {
> > -			s = sock_l4(c, AF_INET6, IPPROTO_ICMPV6, NULL, NULL, id,
> > -				    iref.u32);
> > +			const struct in6_addr *bind_addr = NULL;
> > +			const char *bind_if;
> > +
> > +			bind_if = *c->ip6.ifname_out ? c->ip6.ifname_out : NULL;
> > +
> > +			if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr_out))
> > +				bind_addr = &c->ip6.addr_out;
> > +
> > +			s = sock_l4(c, AF_INET6, IPPROTO_ICMPV6, bind_addr,
> > +				    bind_if, id, iref.u32);  
> 
> Gitto.

Interesting typo. :)

> >  			if (s < 0)
> >  				goto fail_sock;
> >  			if (s > SOCKET_MAX) {
> > diff --git a/passt.1 b/passt.1
> > index f317c33..5c97f30 100644
> > --- a/passt.1
> > +++ b/passt.1
> > @@ -183,6 +183,25 @@ Use host interface \fIname\fR to derive addresses and routes.
> >  Default is to use the interfaces with the first default routes for each IP
> >  version.
> >  
> > +.TP
> > +.BR \-o ", " \-\-outbound " " \fIaddr
> > +Use an IPv4 \fIaddr\fR as source address for IPv4 outbound TCP connections, UDP
> > +flows, ICMP requests, or an IPv6 \fIaddr\fR for IPv6 ones, by binding outbound
> > +sockets to it.
> > +This option can be specified zero (for defaults) to two times (once for IPv4,
> > +once for IPv6).
> > +By default, the source address is selected by the routing tables.
> > +
> > +.TP
> > +.BR \-\-outbound-if4 " " \fIname
> > +Bind IPv4 outbound sockets to host interface \fIname\fR.
> > +By default, the interface given by the default route is selected.
> > +
> > +.TP
> > +.BR \-\-outbound-if6 " " \fIname
> > +Bind IPv6 outbound sockets to host interface \fIname\fR.
> > +By default, the interface given by the default route is selected.
> > +
> >  .TP
> >  .BR \-D ", " \-\-dns " " \fIaddr
> >  Use \fIaddr\fR (IPv4 or IPv6) for DHCP, DHCPv6, NDP or DNS forwarding, as
> > diff --git a/passt.h b/passt.h
> > index cc60c84..b73f4ff 100644
> > --- a/passt.h
> > +++ b/passt.h
> > @@ -106,6 +106,8 @@ enum passt_modes {
> >   * @dns:		DNS addresses for DHCP, zero-terminated, network order
> >   * @dns_match:		Forward DNS query if sent to this address, network order
> >   * @dns_host:		Use this DNS on the host for forwarding, network order
> > + * @addr_out:		Optional source address for outbound traffic
> > + * @ifname_out:		Optional interface name to bind outbound sockets to
> >   */
> >  struct ip4_ctx {
> >  	struct in_addr addr;
> > @@ -115,6 +117,9 @@ struct ip4_ctx {
> >  	struct in_addr dns[MAXNS + 1];
> >  	struct in_addr dns_match;
> >  	struct in_addr dns_host;
> > +
> > +	struct in_addr addr_out;
> > +	char ifname_out[IFNAMSIZ];  
> 
> Again, I think we should just use ip4_ctx::addr as the outbound
> address, with an additional "dhcp_addr" if we must.
> 
> >  };
> >  
> >  /**
> > @@ -127,6 +132,8 @@ struct ip4_ctx {
> >   * @dns:		DNS addresses for DHCPv6 and NDP, zero-terminated
> >   * @dns_match:		Forward DNS query if sent to this address
> >   * @dns_host:		Use this DNS on the host for forwarding
> > + * @addr_out:		Optional source address for outbound traffic
> > + * @ifname_out:		Optional interface name to bind outbound sockets to
> >   */
> >  struct ip6_ctx {
> >  	struct in6_addr addr;
> > @@ -137,6 +144,9 @@ struct ip6_ctx {
> >  	struct in6_addr dns[MAXNS + 1];
> >  	struct in6_addr dns_match;
> >  	struct in6_addr dns_host;
> > +
> > +	struct in6_addr addr_out;
> > +	char ifname_out[IFNAMSIZ];  
> 
> Ditto.
> 
> >  };
> >  
> >  #include <netinet/if_ether.h>
> > diff --git a/tcp.c b/tcp.c
> > index b674311..8e8d653 100644
> > --- a/tcp.c
> > +++ b/tcp.c
> > @@ -1946,6 +1946,61 @@ static uint16_t tcp_conn_tap_mss(const struct ctx *c,
> >  	return MIN(mss, USHRT_MAX);
> >  }
> >  
> > +/**
> > + * tcp_bind_outbound() - Bind socket to outbound address and interface if given
> > + * @c:		Execution context
> > + * @s:		Outbound TCP socket
> > + * @af:		Address family
> > + */
> > +static void tcp_bind_outbound(const struct ctx *c, int s, sa_family_t af)
> > +{
> > +	if (af == AF_INET) {
> > +		if (!IN4_IS_ADDR_UNSPECIFIED(&c->ip4.addr_out)) {
> > +			struct sockaddr_in addr4 = {
> > +				.sin_family = AF_INET,
> > +				.sin_port = 0,
> > +				.sin_addr = c->ip4.addr_out,
> > +			};
> > +
> > +			if (bind(s, (struct sockaddr *)&addr4, sizeof(addr4))) {
> > +				debug("Can't bind IPv4 TCP socket address: %s",
> > +				      strerror(errno));
> > +			}
> > +		}
> > +
> > +		if (*c->ip4.ifname_out) {
> > +			if (setsockopt(s, SOL_SOCKET, SO_BINDTODEVICE,
> > +				       c->ip4.ifname_out,
> > +				       strlen(c->ip4.ifname_out))) {
> > +				debug("Can't bind IPv4 TCP socket to interface:"
> > +				      " %s", strerror(errno));
> > +			}
> > +		}
> > +	} else if (af == AF_INET6) {
> > +		if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr_out)) {
> > +			struct sockaddr_in6 addr6 = {
> > +				.sin6_family = AF_INET6,
> > +				.sin6_port = 0,
> > +				.sin6_addr = c->ip6.addr_out,
> > +			};
> > +
> > +			if (bind(s, (struct sockaddr *)&addr6, sizeof(addr6))) {
> > +				debug("Can't bind IPv6 TCP socket address: %s",
> > +				      strerror(errno));
> > +			}
> > +		}
> > +
> > +		if (*c->ip6.ifname_out) {
> > +			if (setsockopt(s, SOL_SOCKET, SO_BINDTODEVICE,
> > +				       c->ip6.ifname_out,
> > +				       strlen(c->ip6.ifname_out))) {
> > +				debug("Can't bind IPv6 TCP socket to interface:"
> > +				      " %s", strerror(errno));
> > +			}
> > +		}
> > +	}
> > +}
> > +
> >  /**
> >   * tcp_conn_from_tap() - Handle connection request (SYN segment) from tap
> >   * @c:		Execution context
> > @@ -2052,6 +2107,11 @@ static void tcp_conn_from_tap(struct ctx *c, int af, const void *addr,
> >  	if (errno != EADDRNOTAVAIL && errno != EACCES)
> >  		conn_flag(c, conn, LOCAL);
> >  
> > +	if ((af == AF_INET &&  !IN4_IS_ADDR_LOOPBACK(&addr4.sin_addr)) ||
> > +	    (af == AF_INET6 && !IN6_IS_ADDR_LOOPBACK(&addr6.sin6_addr) &&
> > +			       !IN6_IS_ADDR_LINKLOCAL(&addr6.sin6_addr)))
> > +		tcp_bind_outbound(c, s, af);  
> 
> If we have an IPv6 link-local, shouldn't we still do the
> SO_BINDTODEVICE, even though we don't want the bind()?

If an outbound connection uses a link-local address, we use c->ifi6 as
sin6_scope_id (see tcp_conn_from_tap()) -- we need one and it's a
reasonable assumption to use that as that's where we source the first
hop/default gateway from.

But with SO_BINDTODEVICE the kernel resolves the interface name, which
avoids 1. a netlink exchange on every new connection and 2. the need
for the interface to be present at any given time. So I'm not sure we
can actually check that they match in a safe way -- and if there's any
advantage in doing so.

I tend to see the link-local case as completely separate from any
"outbound" consideration, because that's where we make the
guest/container think they're actually talking to a gateway, not to the
"outside world".

> I also wonder if we should allow setting our outbound link-local IPv6
> address, since AIUI there could be multiple on the host.  e.g. allow
> -a to be given three times: one for IPv4, one for IPv6 global and one
> for IPv6 link-local.

Hmm, yes, I guess we should at some point.

> >  	if (connect(s, sa, sl)) {
> >  		if (errno != EINPROGRESS) {
> >  			tcp_rst(c, conn);
> > diff --git a/udp.c b/udp.c
> > index b7cbfdc..99cfc9f 100644
> > --- a/udp.c
> > +++ b/udp.c
> > @@ -843,20 +843,6 @@ int udp_tap_handler(struct ctx *c, int af, const void *addr,
> >  		sa = (struct sockaddr *)&s_in;
> >  		sl = sizeof(s_in);
> >  
> > -		if (!(s = udp_tap_map[V4][src].sock)) {
> > -			union udp_epoll_ref uref = { .udp.port = src };
> > -
> > -			s = sock_l4(c, AF_INET, IPPROTO_UDP, NULL, NULL, src,
> > -				    uref.u32);
> > -			if (s < 0)
> > -				return p->count;
> > -
> > -			udp_tap_map[V4][src].sock = s;
> > -			bitmap_set(udp_act[V4][UDP_ACT_TAP], src);
> > -		}
> > -
> > -		udp_tap_map[V4][src].ts = now->tv_sec;
> > -
> >  		if (IN4_ARE_ADDR_EQUAL(&s_in.sin_addr, &c->ip4.dns_match) &&
> >  		    ntohs(s_in.sin_port) == 53) {
> >  			s_in.sin_addr = c->ip4.dns_host;
> > @@ -868,13 +854,37 @@ int udp_tap_handler(struct ctx *c, int af, const void *addr,
> >  			else
> >  				s_in.sin_addr = c->ip4.addr_seen;
> >  		}
> > +
> > +		if (!(s = udp_tap_map[V4][src].sock)) {
> > +			union udp_epoll_ref uref = { .udp.port = src };
> > +			in_addr_t bind_addr = { 0 };
> > +			const char *bind_if = NULL;
> > +
> > +			if (!IN6_IS_ADDR_LOOPBACK(&s_in.sin_addr) &&
> > +			    *c->ip6.ifname_out)
> > +				bind_if = c->ip6.ifname_out;
> > +
> > +			if (!IN4_IS_ADDR_UNSPECIFIED(&c->ip4.addr_out) &&
> > +			    !IN4_IS_ADDR_LOOPBACK(&s_in.sin_addr))
> > +				bind_addr = c->ip4.addr_out.s_addr;
> > +
> > +			s = sock_l4(c, AF_INET, IPPROTO_UDP, &bind_addr,
> > +				    bind_if, src, uref.u32);
> > +			if (s < 0)
> > +				return p->count;
> > +
> > +			udp_tap_map[V4][src].sock = s;
> > +			bitmap_set(udp_act[V4][UDP_ACT_TAP], src);
> > +		}
> > +
> > +		udp_tap_map[V4][src].ts = now->tv_sec;
> >  	} else {
> >  		s_in6 = (struct sockaddr_in6) {
> >  			.sin6_family = AF_INET6,
> >  			.sin6_port = uh->dest,
> >  			.sin6_addr = *(struct in6_addr *)addr,
> >  		};
> > -		const void *bind_addr = &in6addr_any;
> > +		const struct in6_addr *bind_addr = &in6addr_any;
> >  
> >  		sa = (struct sockaddr *)&s_in6;
> >  		sl = sizeof(s_in6);
> > @@ -898,9 +908,19 @@ int udp_tap_handler(struct ctx *c, int af, const void *addr,
> >  		if (!(s = udp_tap_map[V6][src].sock)) {
> >  			union udp_epoll_ref uref = { .udp.v6 = 1,
> >  						     .udp.port = src };
> > +			const char *bind_if = NULL;
> > +
> > +			if (!IN6_IS_ADDR_LOOPBACK(&s_in6.sin6_addr) &&
> > +			    *c->ip6.ifname_out)
> > +				bind_if = c->ip6.ifname_out;
> > +
> > +			if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr_out) &&
> > +			    !IN6_IS_ADDR_LOOPBACK(&s_in6.sin6_addr) &&
> > +			    !IN6_IS_ADDR_LINKLOCAL(&s_in6.sin6_addr))
> > +				bind_addr = &c->ip6.addr_out;
> >  
> > -			s = sock_l4(c, AF_INET6, IPPROTO_UDP, bind_addr, NULL,
> > -				    src, uref.u32);
> > +			s = sock_l4(c, AF_INET6, IPPROTO_UDP, &bind_addr,  
> 
> bind_addr is already a pointer, I don't think you want the '&' here.

Okay, at least this is fixed. :)

> > +				    bind_if, src, uref.u32);
> >  			if (s < 0)
> >  				return p->count;
> >    

-- 
Stefano