netdev - Re: [PATCH net] net: dsa: fix panic when port leaves a bridge

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Date:   Mon, 14 Mar 2022 16:42:37 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Marek Behún <kabel@...nel.org>
CC:     Tobias Waldekranz <tobias@...dekranz.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Andrew Lunn <andrew@...n.ch>,
        Jan Bětík <hagrid@...ne.us>
Subject: Re: [PATCH net] net: dsa: fix panic when port leaves a bridge

On Mon, Mar 14, 2022 at 05:34:33PM +0100, Marek Behún wrote:
> On Mon, 14 Mar 2022 16:17:06 +0000
> Vladimir Oltean <vladimir.oltean@....com> wrote:
> 
> > On Mon, Mar 14, 2022 at 05:05:29PM +0100, Marek Behún wrote:
> > > On Mon, 14 Mar 2022 16:48:47 +0100
> > > Tobias Waldekranz <tobias@...dekranz.com> wrote:
> > >   
> > > > On Mon, Mar 14, 2022 at 16:34, Marek Behún <kabel@...nel.org> wrote:  
> > > > > Fix a data structure breaking / NULL-pointer dereference in
> > > > > dsa_switch_bridge_leave().
> > > > >
> > > > > When a DSA port leaves a bridge, dsa_switch_bridge_leave() is called by
> > > > > notifier for every DSA switch that contains ports that are in the
> > > > > bridge.
> > > > >
> > > > > But the part of the code that unsets vlan_filtering expects that the ds
> > > > > argument refers to the same switch that contains the leaving port.
> > > > >
> > > > > This leads to various problems, including a NULL pointer dereference,
> > > > > which was observed on Turris MOX with 2 switches (one with 8 user ports
> > > > > and another with 4 user ports).
> > > > >
> > > > > Thus we need to move the vlan_filtering change code to the non-crosschip
> > > > > branch.
> > > > >
> > > > > Fixes: d371b7c92d190 ("net: dsa: Unset vlan_filtering when ports leave the bridge")
> > > > > Reported-by: Jan Bětík <hagrid@...ne.us>
> > > > > Signed-off-by: Marek Behún <kabel@...nel.org>
> > > > > ---    
> > > > 
> > > > Hi Marek,
> > > > 
> > > > I ran into the same issue a while back and fixed it (or at least thought
> > > > I did) in 108dc8741c20. Has that been applied to your tree? Maybe I
> > > > missed some tag that caused it to not be back-ported?  
> > > 
> > > It wasn't applied because I was working with net, not net-next.
> > > 
> > > Very well. We will need to get this backported to stable, though.
> > > 
> > > Marek  
> > 
> > Who can send Tobias's 2 patches to linux-stable branches for 5.4 and higher?
> 
> I can, but I thought it should only be done after it gets merged to
> Linus' master.

Ah, now I re-read Tobias' discussion with Jakub from the cover letter.
I've never seen that procedure in action, to be honest, let's see how it goes.