From: David Gibson <david@gibson.dropbear.id.au>
To: Stefano Brivio <sbrivio@redhat.com>, passt-dev@passt.top
Cc: Paul Holzinger <pholzing@redhat.com>,
David Gibson <david@gibson.dropbear.id.au>
Subject: [PATCH 18/22] Don't take "our" MAC address from the host
Date: Fri, 16 Aug 2024 15:39:59 +1000 [thread overview]
Message-ID: <20240816054004.1335006-19-david@gibson.dropbear.id.au> (raw)
In-Reply-To: <20240816054004.1335006-1-david@gibson.dropbear.id.au>
When sending frames to the guest over the tap link, we need a source MAC
address. Currently we take that from the MAC address of the main interface
on the host, but that doesn't actually make much sense:
* We can't preserve the real MAC address of packets from anywhere
external so there's no transparency case here
* In fact, it's confusingly different from how we handle IP addresses:
whereas we give the guest the same IP as the host, we're making the
host's MAC the one MAC that the guest *can't* use for itself.
* We already need a fallback case if the host doesn't have an Ethernet
like MAC (e.g. if it's connected via a point to point interface, such
as a wireguard VPN).
Change to just just use an arbitrary fixed MAC address - I've picked
9a:55:9a:55:9a:55. It's simpler and has the small advantage of making
the fact that passt/pasta is in use typically obvious from guest side
packet dumps. This can still, of course, be overridden with the -M option.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
conf.c | 40 +++++-----------------------------------
passt.h | 7 +++++++
util.h | 1 -
3 files changed, 12 insertions(+), 36 deletions(-)
diff --git a/conf.c b/conf.c
index 9f962fc8..b1c58d5b 100644
--- a/conf.c
+++ b/conf.c
@@ -612,12 +612,10 @@ static int conf_ip4_prefix(const char *arg)
* conf_ip4() - Verify or detect IPv4 support, get relevant addresses
* @ifi: Host interface to attempt (0 to determine one)
* @ip4: IPv4 context (will be written)
- * @mac: MAC address to use (written if unset)
*
* Return: Interface index for IPv4, or 0 on failure.
*/
-static unsigned int conf_ip4(unsigned int ifi,
- struct ip4_ctx *ip4, unsigned char *mac)
+static unsigned int conf_ip4(unsigned int ifi, struct ip4_ctx *ip4)
{
if (!ifi)
ifi = nl_get_ext_if(nl_sock, AF_INET);
@@ -662,20 +660,6 @@ static unsigned int conf_ip4(unsigned int ifi,
ip4->our_tap_addr = ip4->gw;
- if (MAC_IS_ZERO(mac)) {
- int rc = nl_link_get_mac(nl_sock, ifi, mac);
- if (rc < 0) {
- char ifname[IFNAMSIZ];
-
- err("Couldn't discover MAC address for %s: %s",
- if_indextoname(ifi, ifname), strerror(-rc));
- return 0;
- }
-
- if (MAC_IS_ZERO(mac))
- memcpy(mac, MAC_LAA, ETH_ALEN);
- }
-
if (IN4_IS_ADDR_UNSPECIFIED(&ip4->addr))
return 0;
@@ -686,12 +670,10 @@ static unsigned int conf_ip4(unsigned int ifi,
* conf_ip6() - Verify or detect IPv6 support, get relevant addresses
* @ifi: Host interface to attempt (0 to determine one)
* @ip6: IPv6 context (will be written)
- * @mac: MAC address to use (written if unset)
*
* Return: Interface index for IPv6, or 0 on failure.
*/
-static unsigned int conf_ip6(unsigned int ifi,
- struct ip6_ctx *ip6, unsigned char *mac)
+static unsigned int conf_ip6(unsigned int ifi, struct ip6_ctx *ip6)
{
int prefix_len = 0;
int rc;
@@ -726,19 +708,6 @@ static unsigned int conf_ip6(unsigned int ifi,
if (IN6_IS_ADDR_LINKLOCAL(&ip6->gw))
ip6->our_tap_ll = ip6->gw;
- if (MAC_IS_ZERO(mac)) {
- rc = nl_link_get_mac(nl_sock, ifi, mac);
- if (rc < 0) {
- char ifname[IFNAMSIZ];
- err("Couldn't discover MAC address for %s: %s",
- if_indextoname(ifi, ifname), strerror(-rc));
- return 0;
- }
-
- if (MAC_IS_ZERO(mac))
- memcpy(mac, MAC_LAA, ETH_ALEN);
- }
-
if (IN6_IS_ADDR_UNSPECIFIED(&ip6->addr) ||
IN6_IS_ADDR_UNSPECIFIED(&ip6->our_tap_ll))
return 0;
@@ -1289,6 +1258,7 @@ void conf(struct ctx *c, int argc, char **argv)
c->tcp.fwd_in.mode = c->tcp.fwd_out.mode = FWD_UNSET;
c->udp.fwd_in.mode = c->udp.fwd_out.mode = FWD_UNSET;
+ memcpy(c->our_tap_mac, MAC_OUR_LAA, ETH_ALEN);
optind = 1;
do {
@@ -1659,9 +1629,9 @@ void conf(struct ctx *c, int argc, char **argv)
nl_sock_init(c, false);
if (!v6_only)
- c->ifi4 = conf_ip4(ifi4, &c->ip4, c->our_tap_mac);
+ c->ifi4 = conf_ip4(ifi4, &c->ip4);
if (!v4_only)
- c->ifi6 = conf_ip6(ifi6, &c->ip6, c->our_tap_mac);
+ c->ifi6 = conf_ip6(ifi6, &c->ip6);
if ((!c->ifi4 && !c->ifi6) ||
(*c->ip4.ifname_out && !c->ifi4) ||
(*c->ip6.ifname_out && !c->ifi6))
diff --git a/passt.h b/passt.h
index ecfed1e7..c6c67ffc 100644
--- a/passt.h
+++ b/passt.h
@@ -26,6 +26,13 @@ union epoll_ref;
#include "tcp.h"
#include "udp.h"
+/* Default address for our end on the tap interface. Bit 0 of byte 0 must be 0
+ * (unicast) and bit 1 of byte 1 must be 1 (locally administered). Otherwise
+ * it's arbitrary.
+ */
+#define MAC_OUR_LAA \
+ ((uint8_t [ETH_ALEN]){0x9a, 0x55, 0x9a, 0x55, 0x9a, 0x55})
+
/**
* union epoll_ref - Breakdown of reference for epoll fd bookkeeping
* @type: Type of fd (tells us what to do with events)
diff --git a/util.h b/util.h
index c1748074..899496e3 100644
--- a/util.h
+++ b/util.h
@@ -96,7 +96,6 @@
#define PORT_IS_EPHEMERAL(port) ((port) >= PORT_EPHEMERAL_MIN)
#define MAC_ZERO ((uint8_t [ETH_ALEN]){ 0 })
-#define MAC_LAA ((uint8_t [ETH_ALEN]){ BIT(1), 0, 0, 0, 0, 0 })
#define MAC_IS_ZERO(addr) (!memcmp((addr), MAC_ZERO, ETH_ALEN))
#ifndef __bswap_constant_16
--
@@ -96,7 +96,6 @@
#define PORT_IS_EPHEMERAL(port) ((port) >= PORT_EPHEMERAL_MIN)
#define MAC_ZERO ((uint8_t [ETH_ALEN]){ 0 })
-#define MAC_LAA ((uint8_t [ETH_ALEN]){ BIT(1), 0, 0, 0, 0, 0 })
#define MAC_IS_ZERO(addr) (!memcmp((addr), MAC_ZERO, ETH_ALEN))
#ifndef __bswap_constant_16
--
2.46.0
next prev parent reply other threads:[~2024-08-16 5:40 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-08-16 5:39 [PATCH 00/22] RFC: Allow configuration of special case NATs David Gibson
2024-08-16 5:39 ` [PATCH 01/22] treewide: Use "our address" instead of "forwarding address" David Gibson
2024-08-18 15:44 ` Stefano Brivio
2024-08-19 1:28 ` David Gibson
2024-08-16 5:39 ` [PATCH 02/22] util: Helper for formatting MAC addresses David Gibson
2024-08-18 15:44 ` Stefano Brivio
2024-08-19 1:29 ` David Gibson
2024-08-16 5:39 ` [PATCH 03/22] treewide: Rename MAC address fields for clarity David Gibson
2024-08-18 15:45 ` Stefano Brivio
2024-08-19 1:36 ` David Gibson
2024-08-16 5:39 ` [PATCH 04/22] treewide: Use struct assignment instead of memcpy() for IP addresses David Gibson
2024-08-18 15:45 ` Stefano Brivio
2024-08-19 1:38 ` David Gibson
2024-08-16 5:39 ` [PATCH 05/22] conf: Use array indices rather than pointers for DNS array slots David Gibson
2024-08-16 5:39 ` [PATCH 06/22] conf: More accurately count entries added in get_dns() David Gibson
2024-08-16 5:39 ` [PATCH 07/22] conf: Move DNS array bounds checks into add_dns[46] David Gibson
2024-08-16 5:39 ` [PATCH 08/22] conf: Move adding of a nameserver from resolv.conf into subfunction David Gibson
2024-08-16 5:39 ` [PATCH 09/22] conf: Correct setting of dns_match address in add_dns6() David Gibson
2024-08-16 5:39 ` [PATCH 10/22] conf: Treat --dns addresses as guest visible addresses David Gibson
2024-08-16 5:39 ` [PATCH 11/22] conf: Remove incorrect initialisation of addr_ll_seen David Gibson
2024-08-16 5:39 ` [PATCH 12/22] util: Correct sock_l4() binding for link local addresses David Gibson
2024-08-20 0:14 ` Stefano Brivio
2024-08-20 1:29 ` David Gibson
2024-08-16 5:39 ` [PATCH 13/22] treewide: Change misleading 'addr_ll' name David Gibson
2024-08-20 0:15 ` Stefano Brivio
2024-08-20 1:30 ` David Gibson
2024-08-16 5:39 ` [PATCH 14/22] Clarify which addresses in ip[46]_ctx are meaningful where David Gibson
2024-08-16 5:39 ` [PATCH 15/22] Initialise our_tap_ll to ip6.gw when suitable David Gibson
2024-08-16 5:39 ` [PATCH 16/22] fwd: Helpers to clarify what host addresses aren't guest accessible David Gibson
2024-08-20 19:56 ` Stefano Brivio
2024-08-21 1:40 ` David Gibson
2024-08-16 5:39 ` [PATCH 17/22] fwd: Split notion of "our tap address" from gateway for IPv4 David Gibson
2024-08-20 19:56 ` Stefano Brivio
2024-08-21 1:56 ` David Gibson
2024-08-16 5:39 ` David Gibson [this message]
2024-08-16 5:40 ` [PATCH 19/22] conf, fwd: Split notion of gateway/router from guest-visible host address David Gibson
2024-08-20 19:56 ` Stefano Brivio
2024-08-21 1:59 ` David Gibson
2024-08-16 5:40 ` [PATCH 20/22] conf: Allow address remapped to host to be configured David Gibson
2024-08-20 19:56 ` Stefano Brivio
2024-08-21 2:23 ` David Gibson
2024-08-16 5:40 ` [PATCH 21/22] fwd: Distinguish translatable from untranslatable addresses on inbound David Gibson
2024-08-16 5:40 ` [PATCH 22/22] fwd, conf: Allow NAT of the guest's assigned address David Gibson
2024-08-20 19:56 ` Stefano Brivio
2024-08-21 2:28 ` David Gibson
2024-08-16 14:45 ` [PATCH 00/22] RFC: Allow configuration of special case NATs Paul Holzinger
2024-08-16 15:03 ` Stefano Brivio
2024-08-17 8:01 ` David Gibson
2024-08-19 8:46 ` David Gibson
2024-08-19 9:27 ` Stefano Brivio
2024-08-19 9:52 ` David Gibson
2024-08-19 13:01 ` Stefano Brivio
2024-08-20 0:42 ` David Gibson
2024-08-20 20:39 ` Stefano Brivio
2024-08-21 2:51 ` David Gibson
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