netdev - Re: [PATCH net] net: bridge: validate the NUD_PERMANENT bit when adding an extern

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Date:   Mon, 9 Aug 2021 15:16:40 +0300
From:   Ido Schimmel <idosch@...sch.org>
To:     Vladimir Oltean <vladimir.oltean@....com>, nikolay@...dia.com
Cc:     netdev@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jiri Pirko <jiri@...nulli.us>, Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <nikolay@...dia.com>,
        bridge@...ts.linux-foundation.org,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        syzbot+9ba1174359adba5a5b7c@...kaller.appspotmail.com
Subject: Re: [PATCH net] net: bridge: validate the NUD_PERMANENT bit when
 adding an extern_learn FDB entry

On Mon, Aug 02, 2021 at 02:17:30AM +0300, Vladimir Oltean wrote:
> diff --git a/net/bridge/br.c b/net/bridge/br.c
> index ef743f94254d..bbab9984f24e 100644
> --- a/net/bridge/br.c
> +++ b/net/bridge/br.c
> @@ -166,7 +166,8 @@ static int br_switchdev_event(struct notifier_block *unused,
>  	case SWITCHDEV_FDB_ADD_TO_BRIDGE:
>  		fdb_info = ptr;
>  		err = br_fdb_external_learn_add(br, p, fdb_info->addr,
> -						fdb_info->vid, false);
> +						fdb_info->vid,
> +						fdb_info->is_local, false);

When 'is_local' was added in commit 2c4eca3ef716 ("net: bridge:
switchdev: include local flag in FDB notifications") it was not
initialized in all the call sites that emit
'SWITCHDEV_FDB_ADD_TO_BRIDGE' notification, so it can contain garbage.

>  		if (err) {
>  			err = notifier_from_errno(err);
>  			break;

[...]

> @@ -1281,6 +1292,10 @@ int br_fdb_external_learn_add(struct net_bridge *br, struct net_bridge_port *p,
>  
>  		if (swdev_notify)
>  			flags |= BIT(BR_FDB_ADDED_BY_USER);
> +
> +		if (is_local)
> +			flags |= BIT(BR_FDB_LOCAL);

I have at least once selftest where I forgot the 'static' keyword:

bridge fdb add de:ad:be:ef:13:37 dev $swp1 master extern_learn vlan 1

This patch breaks the test when run against both the kernel and hardware
data paths. I don't mind patching these tests, but we might get more
reports in the future.

Nik, what do you think?

> +
>  		fdb = fdb_create(br, p, addr, vid, flags);
>  		if (!fdb) {
>  			err = -ENOMEM;
> @@ -1307,6 +1322,9 @@ int br_fdb_external_learn_add(struct net_bridge *br, struct net_bridge_port *p,
>  		if (swdev_notify)
>  			set_bit(BR_FDB_ADDED_BY_USER, &fdb->flags);
>  
> +		if (is_local)
> +			set_bit(BR_FDB_LOCAL, &fdb->flags);
> +
>  		if (modified)
>  			fdb_notify(br, fdb, RTM_NEWNEIGH, swdev_notify);
>  	}
> diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
> index 2b48b204205e..aa64d8d63ca3 100644
> --- a/net/bridge/br_private.h
> +++ b/net/bridge/br_private.h
> @@ -711,7 +711,7 @@ int br_fdb_get(struct sk_buff *skb, struct nlattr *tb[], struct net_device *dev,
>  int br_fdb_sync_static(struct net_bridge *br, struct net_bridge_port *p);
>  void br_fdb_unsync_static(struct net_bridge *br, struct net_bridge_port *p);
>  int br_fdb_external_learn_add(struct net_bridge *br, struct net_bridge_port *p,
> -			      const unsigned char *addr, u16 vid,
> +			      const unsigned char *addr, u16 vid, bool is_local,
>  			      bool swdev_notify);
>  int br_fdb_external_learn_del(struct net_bridge *br, struct net_bridge_port *p,
>  			      const unsigned char *addr, u16 vid,
> -- 
> 2.25.1
>