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network: do not regenerate MAC address if already set by userspace

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When MACAddress= is unspecified, a stable MAC is generated to seed a newly
created netdev. Since existing netdevs are reconfigured on reload/restart,
this seed got re-applied to an already existing interface, conflicting with
an explicit MACAddress= from the matching .network file and flipping MAC.

Now, when MACAddress= is unspecified, only generate a new address if
addr_assign_type is not NET_ADDR_SET (i.e. not already set by userspace). On
first creation the interface does not exist yet, so this is a no-op and the
address is generated as before. Mirrors src/udev/net/link-config.c.

Fixes: #42457
This commit is contained in:
Shihao Ren
2026-07-10 15:26:27 +08:00
committed by Yu Watanabe
parent 70cfb11d4b
commit dbb59dab73
1 changed files with 24 additions and 0 deletions
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24
src/network/netdev/netdev.c
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@@ -1,6 +1,7 @@
/* SPDX-License-Identifier: LGPL-2.1-or-later */
#include <linux/if_arp.h>
#include <linux/netdevice.h>
#include <unistd.h>
#include "sd-netlink.h"
@@ -14,6 +15,7 @@
#include "condition.h"
#include "conf-files.h"
#include "conf-parser.h"
#include "device-private.h"
#include "dummy.h"
#include "fou-tunnel.h"
#include "geneve.h"
@@ -575,6 +577,21 @@ int netdev_generate_hw_addr(
if (!IN_SET(NETDEV_VTABLE(netdev)->iftype, ARPHRD_ETHER, ARPHRD_INFINIBAND))
goto finalize;
/* If the interface already exists and its MAC address has been set by userspace
* (e.g. through MACAddress= in the matching .network file, or manually), do not
* generate a new address. Otherwise, on reconfiguration the generated address would
* override the one set by userspace and, as they differ, both would be re-applied on
* every reload/restart. See issue #42457. */
Link *link;
unsigned addr_assign_type;
if (link_get_by_index(netdev->manager, netdev->ifindex, &link) >= 0 &&
link->dev &&
device_get_sysattr_unsigned(link->dev, "addr_assign_type", &addr_assign_type) >= 0 &&
addr_assign_type == NET_ADDR_SET) {
log_netdev_debug(netdev, "MAC address is already set by userspace, not generating a new one.");
goto finalize;
}
r = net_get_unique_predictable_data_from_name(name, &HASH_KEY, &result);
if (r < 0) {
log_netdev_warning_errno(netdev, r,
@@ -964,6 +981,13 @@ static int independent_netdev_process_request(Request *req, Link *link, void *us
return 1; /* Skip this request. */
}
Link *existing;
if (link_get_by_index(netdev->manager, netdev->ifindex, &existing) >= 0 &&
IN_SET(existing->state,
LINK_STATE_PENDING, /* Already exists and is being processed by udevd. Postpone the request. */
LINK_STATE_LINGER)) /* Already removed; wait for the stale information to be cleared. */
return 0;
r = netdev_is_ready_to_create(netdev, NULL);
if (r <= 0)
return r;