On Thu, 2020-10-15 at 20:33 +0300, Vladimir Oltean wrote: > Switchdev drivers often have different VLAN semantics than the bridge. > For example, consider this: > > ip link add br0 type bridge > ip link set swp0 master br0 > bridge mdb add dev br0 port swp0 grp 01:02:03:04:05:06 permanent > ip link del br0 > [ 26.085816] mscc_felix 0000:00:00.5 swp0: failed (err=-2) to del object (id=2) > > This is because the mscc_ocelot driver, when VLAN awareness is disabled, > classifies all traffic to the port-based VLAN (pvid). The pvid is 0 when > the port is standalone, and it is inherited from the bridge default pvid > (which is 1 by default, but it may take other values) when it joins the > VLAN-unaware bridge, and then the pvid resets to 0 when the port leaves > the bridge again. > > Now because the mscc_ocelot switch classifies all traffic to its private > pvid, it needs to translate between the vid that the mdb comes with, and > the vid that will actually be programmed into hardware. The bridge uses > the vid of 0 in VLAN-unaware mode, while the hardware uses the pvid > inherited from the bridge, that's the difference. > > So what will happen is: > > Step 1 (addition): > br_mdb_notify(RTM_NEWMDB) > -> ocelot_port_mdb_add(mdb->addr=01:02:03:04:05:06, mdb->vid=0) > -> mdb->vid is remapped from 0 to 1 and installed into ocelot->multicast > > Step 2 (removal): > del_nbp > -> netdev_upper_dev_unlink(dev, br->dev) > -> ocelot_port_bridge_leave > -> ocelot_port_set_pvid(ocelot, port, 0) > -> br_multicast_del_port is called and the switchdev notifier is > deferred for some time later > -> ocelot_port_mdb_del(mdb->addr=01:02:03:04:05:06, mdb->vid=0) > -> mdb->vid is remapped from 0 to 0, the port pvid (!!!) > -> the remapped mdb (addr=01:02:03:04:05:06, vid=0) is not found > inside the ocelot->multicast list, and -ENOENT is returned > > So the problem is that mscc_ocelot assumes that the port is removed > _after_ the multicast entries have been deleted. And this is not an > unreasonable assumption, presumably it isn't the only switchdev that > needs to remap the vid. So we can reorder the teardown path in order > for that assumption to hold true. > > Since br_mdb_notify() issues a SWITCHDEV_F_DEFER operation, we must move > the call not only before netdev_upper_dev_unlink(), but in fact before > switchdev_deferred_process(). > > Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx> > --- > net/bridge/br_if.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > It can potentially use after free, multicast resources (per-cpu stats) are freed in br_multicast_del_port() and can be used due to a race with port state sync on other CPUs since the handler can still process packets. That has a chance of happening if vlans are not used. Interesting that br_stp_disable_port() calls br_multicast_disable_port() which flushes all non-permanent mdb entries, so I'm guessing you have problem only with permanent ones? Perhaps we can flush them all before. Either by passing an argument to br_stp_disable_port() that we're deleting the port which will be passed down to br_multicast_disable_port() or by calling an additional helper to flush all which can be re-used by both disable_port() and stop_multicast() calls. Adding an argument to br_stp_disable_port() to be passed down sounds cleaner to me. What do you think? Cheers, Nik
