[PATCH net] bonding: do not clear curr_active_slave prematurely when releasing all slaves

[Eric Dumazet <edumazet@google.com>]

When releasing all slaves during bond destruction (all == true),
__bond_release_one() unconditionally clears bond->curr_active_slave to
NULL in every iteration.

If a backup slave is released before the active slave,
bond_alb_deinit_slave() triggers rlb_teach_disabled_mac_on_primary(),
which increments the active slave dev promiscuity counter and sets
bond_info->primary_is_promisc = 1.

Because bond->curr_active_slave was prematurely cleared to NULL when
releasing the backup slave, the subsequent iteration releasing the active
slave evaluates oldcurrent as NULL, so bond_change_active_slave(bond, NULL)
is skipped. Consequently, bond_alb_handle_active_change() is never called
to decrement the promiscuity counter, permanently leaking promiscuous
mode on the physical device after bond teardown.

When oldcurrent == slave, bond_change_active_slave(bond, NULL) already sets
bond->curr_active_slave to NULL. We only need to avoid selecting a new
active slave when all == true. Replace the if (all) branch with
if (!all && oldcurrent == slave).

Fixes: 0896341a44bf ("bonding: fix bond_release_all inconsistencies")
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
Cc: Jay Vosburgh <jv@jvosburgh.net>
---
 drivers/net/bonding/bond_main.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index c23cf18a996a..1e5ab3454872 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -2517,9 +2517,7 @@ static int __bond_release_one(struct net_device *bond_dev,
 		bond_alb_deinit_slave(bond, slave);
 	}
 
-	if (all) {
-		RCU_INIT_POINTER(bond->curr_active_slave, NULL);
-	} else if (oldcurrent == slave) {
+	if (!all && oldcurrent == slave) {
 		/* Note that we hold RTNL over this sequence, so there
 		 * is no concern that another slave add/remove event
 		 * will interfere.
-- 
2.55.0.970.g62bdec98f9-goog