macvlan: fix passthru promiscuity accounting while down

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: df8ef8f3aaa6 ("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>

0 files changed, 0 insertions, 0 deletions