netdev - Re: [PATCH net] net: bridge: deny dev_set_mac

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Date:   Tue, 03 Dec 2019 11:22:45 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     nikolay@...ulusnetworks.com
Cc:     netdev@...r.kernel.org, roopa@...ulusnetworks.com,
        bridge@...ts.linux-foundation.org, syzkaller-bugs@...glegroups.com,
        stephen@...workplumber.org,
        syzbot+2add91c08eb181fea1bf@...kaller.appspotmail.com
Subject: Re: [PATCH net] net: bridge: deny dev_set_mac_address() when
 unregistering

From: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Date: Tue,  3 Dec 2019 16:48:06 +0200

> We have an interesting memory leak in the bridge when it is being
> unregistered and is a slave to a master device which would change the
> mac of its slaves on unregister (e.g. bond, team). This is a very
> unusual setup but we do end up leaking 1 fdb entry because
> dev_set_mac_address() would cause the bridge to insert the new mac address
> into its table after all fdbs are flushed, i.e. after dellink() on the
> bridge has finished and we call NETDEV_UNREGISTER the bond/team would
> release it and will call dev_set_mac_address() to restore its original
> address and that in turn will add an fdb in the bridge.
> One fix is to check for the bridge dev's reg_state in its
> ndo_set_mac_address callback and return an error if the bridge is not in
> NETREG_REGISTERED.
> 
> Easy steps to reproduce:
>  1. add bond in mode != A/B
>  2. add any slave to the bond
>  3. add bridge dev as a slave to the bond
>  4. destroy the bridge device
> 
> Trace:
>  unreferenced object 0xffff888035c4d080 (size 128):
 ...
> Fixes: 43598813386f ("bridge: add local MAC address to forwarding table (v2)")
> Reported-by: syzbot+2add91c08eb181fea1bf@...kaller.appspotmail.com
> Signed-off-by: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>

Looks good, applied and queued up for -stable.

Thanks.