macsec: fix promiscuity refcount leak in macsec_dev_open()

When a MACsec interface with IFF_PROMISC set is brought up on top of a
device that has hardware offload enabled, macsec_dev_open() first calls
dev_set_promiscuity(real_dev, 1) and then propagates the open to the
offload device. If that propagation fails, the error path jumps to the
clear_allmulti label, which only reverts allmulti and the unicast
address. The promiscuity taken on the lower device is never dropped, so
real_dev is left permanently stuck in promiscuous mode. Its promiscuity
count can no longer be balanced from software.

Add a clear_promisc label that drops the promiscuity reference and
route the two offload failure paths to it. The dev_set_promiscuity()
failure itself still jumps to clear_allmulti, since on that failure the
count was not incremented.

Fixes: 3cf3227 ("net: macsec: hardware offloading infrastructure")
Cc: stable@vger.kernel.org
Signed-off-by: James Raphael Tiovalen <jamestiotio@gmail.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://patch.msgid.link/20260705113629.187490-1-jamestiotio@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: jamestiotio

drivers/net/macsec.c

@@ -3615,19 +3615,22 @@ static int macsec_dev_open(struct net_device *dev)
 		ops = macsec_get_ops(netdev_priv(dev), &ctx);
 		if (!ops) {
 			err = -EOPNOTSUPP;
-			goto clear_allmulti;
+			goto clear_promisc;
 		}
 
 		ctx.secy = &macsec->secy;
 		err = macsec_offload(ops->mdo_dev_open, &ctx);
 		if (err)
-			goto clear_allmulti;
+			goto clear_promisc;
 	}
 
 	if (netif_carrier_ok(real_dev))
 		netif_carrier_on(dev);
 
 	return 0;
+clear_promisc:
+	if (dev->flags & IFF_PROMISC)
+		dev_set_promiscuity(real_dev, -1);
 clear_allmulti:
 	if (dev->flags & IFF_ALLMULTI)
 		dev_set_allmulti(real_dev, -1);