From: Vladimir Oltean <vladimir.oltean@xxxxxxx> commit 8940e6b669ca1196ce0a0549c819078096390f76 upstream. If the DSA master doesn't support IFF_UNICAST_FLT, then the following call path is possible: dsa_slave_switchdev_event_work -> dsa_port_host_fdb_add -> dev_uc_add -> __dev_set_rx_mode -> __dev_set_promiscuity Since the blamed commit, dsa_slave_switchdev_event_work() no longer holds rtnl_lock(), which triggers the ASSERT_RTNL() from __dev_set_promiscuity(). Taking rtnl_lock() around dev_uc_add() is impossible, because all the code paths that call dsa_flush_workqueue() do so from contexts where the rtnl_mutex is already held - so this would lead to an instant deadlock. dev_uc_add() in itself doesn't require the rtnl_mutex for protection. There is this comment in __dev_set_rx_mode() which assumes so: /* Unicast addresses changes may only happen under the rtnl, * therefore calling __dev_set_promiscuity here is safe. */ but it is from commit 4417da668c00 ("[NET]: dev: secondary unicast address support") dated June 2007, and in the meantime, commit f1f28aa3510d ("netdev: Add addr_list_lock to struct net_device."), dated July 2008, has added &dev->addr_list_lock to protect this instead of the global rtnl_mutex. Nonetheless, __dev_set_promiscuity() does assume rtnl_mutex protection, but it is the uncommon path of what we typically expect dev_uc_add() to do. So since only the uncommon path requires rtnl_lock(), just check ahead of time whether dev_uc_add() would result into a call to __dev_set_promiscuity(), and handle that condition separately. DSA already configures the master interface to be promiscuous if the tagger requires this. We can extend this to also cover the case where the master doesn't handle dev_uc_add() (doesn't support IFF_UNICAST_FLT), and on the premise that we'd end up making it promiscuous during operation anyway, either if a DSA slave has a non-inherited MAC address, or if the bridge notifies local FDB entries for its own MAC address, the address of a station learned on a foreign port, etc. Fixes: 0faf890fc519 ("net: dsa: drop rtnl_lock from dsa_slave_switchdev_event_work") Reported-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx> Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/dsa/master.c | 7 ++++++- net/dsa/port.c | 20 ++++++++++++++------ 2 files changed, 20 insertions(+), 7 deletions(-) --- a/net/dsa/master.c +++ b/net/dsa/master.c @@ -260,11 +260,16 @@ static void dsa_netdev_ops_set(struct ne dev->dsa_ptr->netdev_ops = ops; } +/* Keep the master always promiscuous if the tagging protocol requires that + * (garbles MAC DA) or if it doesn't support unicast filtering, case in which + * it would revert to promiscuous mode as soon as we call dev_uc_add() on it + * anyway. + */ static void dsa_master_set_promiscuity(struct net_device *dev, int inc) { const struct dsa_device_ops *ops = dev->dsa_ptr->tag_ops; - if (!ops->promisc_on_master) + if ((dev->priv_flags & IFF_UNICAST_FLT) && !ops->promisc_on_master) return; rtnl_lock(); --- a/net/dsa/port.c +++ b/net/dsa/port.c @@ -777,9 +777,15 @@ int dsa_port_host_fdb_add(struct dsa_por struct dsa_port *cpu_dp = dp->cpu_dp; int err; - err = dev_uc_add(cpu_dp->master, addr); - if (err) - return err; + /* Avoid a call to __dev_set_promiscuity() on the master, which + * requires rtnl_lock(), since we can't guarantee that is held here, + * and we can't take it either. + */ + if (cpu_dp->master->priv_flags & IFF_UNICAST_FLT) { + err = dev_uc_add(cpu_dp->master, addr); + if (err) + return err; + } return dsa_port_notify(dp, DSA_NOTIFIER_HOST_FDB_ADD, &info); } @@ -796,9 +802,11 @@ int dsa_port_host_fdb_del(struct dsa_por struct dsa_port *cpu_dp = dp->cpu_dp; int err; - err = dev_uc_del(cpu_dp->master, addr); - if (err) - return err; + if (cpu_dp->master->priv_flags & IFF_UNICAST_FLT) { + err = dev_uc_del(cpu_dp->master, addr); + if (err) + return err; + } return dsa_port_notify(dp, DSA_NOTIFIER_HOST_FDB_DEL, &info); } Patches currently in stable-queue which might be from vladimir.oltean@xxxxxxx are queue-5.16/net-dsa-avoid-call-to-__dev_set_promiscuity-while-rtnl_mutex-isn-t-held.patch