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macvlan: fix passthru promiscuity accounting while down

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macvlan_changelink() adjusts the lower device's promiscuity count when
NOPROMISC changes, even if the passthru macvlan is down. The reference
is acquired in macvlan_open() and released in macvlan_stop(), so a down
interface has no reference to change.

Clearing NOPROMISC while down leaves an extra reference after the next
open/stop cycle. Setting it while down can remove a reference held by
another user of the lower device.

Guard the count adjustment with netif_running(dev). Keep storing the
requested flags while down so the next open uses the new setting.

Comparing changelink with open/stop exposed the unmatched count changes;
the same issue was also described in earlier macvlan reviews. A netlink
test on UML reproduced both DOWN cases before the fix and verified the
expected counts afterwards. Repeated flag updates, two open/stop cycles,
deletion and bidirectional small-frame delivery were also checked.

Full x86_64 builds completed with WERROR disabled for allmodconfig, and
WERROR and KASAN disabled for allyesconfig, including the resulting
dependency changes. Neither comparison showed new diagnostics.

Fixes: df8ef8f3aa ("macvlan: add FDB bridge ops and macvlan flags")
Link: https://lore.kernel.org/netdev/179170088566.434549.4699134797461783473@kernel.org/
Link: https://lore.kernel.org/netdev/20261016003009.2692872-1-kuba@kernel.org/
Cc: stable@vger.kernel.org
Signed-off-by: Xia Yan <yanxia@cmss.chinamobile.com>
Reviewed-by: Hangbin Liu <liuhangbin@kylinos.cn>
Link: https://patch.msgid.link/20261022090809.12019-1-yanxia@cmss.chinamobile.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Xia Yan 2026-10-22 17:08:09 +08:00 committed by Jakub Kicinski
parent ef8f0a1d88
commit b6743653d1
1 changed files with 2 additions and 1 deletions
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3
drivers/net/macvlan.c
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@ -1664,7 +1664,8 @@ static int macvlan_changelink(struct net_device *dev,
if (data && data[IFLA_MACVLAN_FLAGS]) {
__u16 flags = nla_get_u16(data[IFLA_MACVLAN_FLAGS]);
bool promisc = (flags ^ vlan->flags) & MACVLAN_FLAG_NOPROMISC;
if (macvlan_passthru(vlan->port) && promisc) {
if (macvlan_passthru(vlan->port) && promisc &&
netif_running(dev)) {
int err;
if (flags & MACVLAN_FLAG_NOPROMISC)