Subject: Re: [PATCH v3 net] net: ipv4/ipv6 addrconf: call igmp{,6}_group_dropped() while dev is still up

From: Ido Schimmel <[email-masked]>
Date: Wed, 12 Apr 2023 16:34:00 +0300

On Tue, Apr 11, 2023 at 05:49:55PM +0300, Vladimir Oltean wrote:
> ipv4 devinet calls ip_mc_down(), and ipv6 calls addrconf_ifdown(), and
> both of these eventually result in calls to dev_mc_del(), either through
> igmp_group_dropped() or igmp6_group_dropped().
> 
> The problem is that dev_mc_del() does call __dev_set_rx_mode(), but this
> will not propagate all the way to the ndo_set_rx_mode() of the device,
> because of this check:
> 
>         /* dev_open will call this function so the list will stay sane. */
>         if (!(dev->flags&IFF_UP))
>                 return;
> 
> and the NETDEV_DOWN notifier is emitted while the interface is already
> down. OTOH we have NETDEV_GOING_DOWN which is emitted a bit earlier -
> see:
> 
> dev_close_many()
> -> __dev_close_many()
>    -> call_netdevice_notifiers(NETDEV_GOING_DOWN, dev);
>    -> dev->flags &= ~IFF_UP;
> -> call_netdevice_notifiers(NETDEV_DOWN, dev);
> 
> Normally this oversight is easy to miss, because the addresses aren't
> lost, just not synced to the device until the next up event.
> 
> DSA does some processing in its dsa_slave_set_rx_mode(), and assumes
> that all addresses that were synced are also unsynced by the time the
> device is unregistered. Due to that assumption not being satisfied,
> the WARN_ON(!list_empty(&dp->mdbs)); from dsa_switch_release_ports()
> triggers, and we leak memory corresponding to the multicast addresses
> that were never synced.
> 
> Minimal reproducer:
> ip link set swp0 up
> ip link set swp0 down
> echo 0000:00:00.5 > /sys/bus/pci/drivers/mscc_felix/unbind

Even with the proposed fix, wouldn't you get the same leak with the
following reproducer?

ip link set dev swp0 up
bridge fdb add 01:02:03:04:05:06 dev swp0 self local
ip link set dev swp0 down
echo 0000:00:00.5 > /sys/bus/pci/drivers/mscc_felix/unbind

If so, I wonder how other drivers that allocate memory in their
ndo_set_rx_mode() deal with this problem. I would imagine that they
flush the addresses in their ndo_stop() or as part of device dismantle.

> 
> The proposal is to respond to that slightly earlier notifier with the
> IGMP address deletion, so that the ndo_set_rx_mode() of the device does
> actually get called.
> 
> Fixes: 5e8a1e03aa4d ("net: dsa: install secondary unicast and multicast addresses as host FDB/MDB")
> Signed-off-by: Vladimir Oltean <[email-masked]>
> ---
> v2->v3:
> Returned to the original strategy, with Ido's modification applied
> (to only touch the netdev notifier values, not the inetaddr notifier
> values).
> 
> v2 at:
> https://patchwork.kernel.org/project/netdevbpf/patch/[email-masked]/
> 
>  net/ipv4/devinet.c  | 2 +-
>  net/ipv6/addrconf.c | 6 +++---
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
> index 5deac0517ef7..679c9819f25b 100644
> --- a/net/ipv4/devinet.c
> +++ b/net/ipv4/devinet.c
> @@ -1588,7 +1588,7 @@ static int inetdev_event(struct notifier_block *this, unsigned long event,
>  		/* Send gratuitous ARP to notify of link change */
>  		inetdev_send_gratuitous_arp(dev, in_dev);
>  		break;
> -	case NETDEV_DOWN:
> +	case NETDEV_GOING_DOWN:
>  		ip_mc_down(in_dev);
>  		break;
>  	case NETDEV_PRE_TYPE_CHANGE:
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 3797917237d0..f4a3b2693d6a 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -3670,12 +3670,12 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
>  		}
>  		break;
>  
> -	case NETDEV_DOWN:
> +	case NETDEV_GOING_DOWN:
>  	case NETDEV_UNREGISTER:
>  		/*
>  		 *	Remove all addresses from this interface.
>  		 */
> -		addrconf_ifdown(dev, event != NETDEV_DOWN);
> +		addrconf_ifdown(dev, event != NETDEV_GOING_DOWN);
>  		break;
>  
>  	case NETDEV_CHANGENAME:
> @@ -6252,7 +6252,7 @@ static void dev_disable_change(struct inet6_dev *idev)
>  
>  	netdev_notifier_info_init(&info, idev->dev);
>  	if (idev->cnf.disable_ipv6)
> -		addrconf_notify(NULL, NETDEV_DOWN, &info);
> +		addrconf_notify(NULL, NETDEV_GOING_DOWN, &info);
>  	else
>  		addrconf_notify(NULL, NETDEV_UP, &info);
>  }
> -- 
> 2.34.1
>