netdev - Re: [PATCH] net: bridge: disable multicast while delete bridge

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Date:   Tue, 3 Nov 2020 16:26:25 +0000
From:   Nikolay Aleksandrov <nikolay@...dia.com>
To:     "menglong8.dong@...il.com" <menglong8.dong@...il.com>,
        Roopa Prabhu <roopa@...dia.com>
CC:     "bridge@...ts.linux-foundation.org" 
        <bridge@...ts.linux-foundation.org>,
        "dong.menglong@....com.cn" <dong.menglong@....com.cn>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: bridge: disable multicast while delete bridge

On Mon, 2020-11-02 at 22:38 +0800, Menglong Dong wrote:
> From: Menglong Dong <dong.menglong@....com.cn>
> 
> This commit seems make no sense, as bridge is destroyed when
> br_multicast_dev_del is called.
> 
> In commit b1b9d366028f
> ("bridge: move bridge multicast cleanup to ndo_uninit"), Xin Long
> fixed the use-after-free panic in br_multicast_group_expired by
> moving br_multicast_dev_del to ndo_uninit. However, that patch is
> not applied to 4.4.X, and the bug exists.
> 
> Fix that bug by disabling multicast in br_multicast_dev_del for
> 4.4.X, and there is no harm for other branches.
> 
> Signed-off-by: Menglong Dong <dong.menglong@....com.cn>
> ---
>  net/bridge/br_multicast.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
> index eae898c3cff7..9992fdff2951 100644
> --- a/net/bridge/br_multicast.c
> +++ b/net/bridge/br_multicast.c
> @@ -3369,6 +3369,7 @@ void br_multicast_dev_del(struct net_bridge *br)
>  	hlist_for_each_entry_safe(mp, tmp, &br->mdb_list, mdb_node)
>  		br_multicast_del_mdb_entry(mp);
>  	hlist_move_list(&br->mcast_gc_list, &deleted_head);
> +	br_opt_toggle(br, BROPT_MULTICAST_ENABLED, false);
>  	spin_unlock_bh(&br->multicast_lock);
>  
>  	br_multicast_gc(&deleted_head);

This doesn't make any sense. It doesn't fix anything.
If 4.4 has a problem then the relevant patches should get backported to it.
We don't add random changes to fix older releases.

Cheers,
 Nik

Nacked-by: Nikolay Aleksandrov <nikolay@...dia.com>