netdev - Re: [PATCH] appletalk: Fix potential refcount leak

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Message-ID: <CANn89iL==crwYiOpcgx=zVG1porMpMt23RCp=_JGpQmxOwK04w@mail.gmail.com>
Date:   Mon, 24 Oct 2022 08:36:13 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Liang He <windhl@....com>
Cc:     davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
        netdev@...r.kernel.org
Subject: Re: [PATCH] appletalk: Fix potential refcount leak

On Mon, Oct 24, 2022 at 8:25 AM Liang He <windhl@....com> wrote:
>
> In atrtr_create(), we have added a dev_hold for the new reference.
> However, based on the code, if the 'rt' is not NULL and its 'dev'
> is not NULL, we should use dev_put() for the replaced reference.
>
> Signed-off-by: Liang He <windhl@....com>
> ---
>  net/appletalk/ddp.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/net/appletalk/ddp.c b/net/appletalk/ddp.c
> index a06f4d4a6f47..7e317d6448d1 100644
> --- a/net/appletalk/ddp.c
> +++ b/net/appletalk/ddp.c
> @@ -564,6 +564,7 @@ static int atrtr_create(struct rtentry *r, struct net_device *devhint)
>         /* Fill in the routing entry */
>         rt->target  = ta->sat_addr;
>         dev_hold(devhint);
> +       dev_put(rt->dev);
>         rt->dev     = devhint;
>         rt->flags   = r->rt_flags;
>         rt->gateway = ga->sat_addr;
>

IMO appletalk is probably completely broken.

atalk_routes_lock is not held while other threads might use rt->dev
and would not expect rt->dev to be changed under them
(atalk_route_packet() )

I would vote to remove it completely, unless someone is willing to
test any change in it.