netdev - Re: [PATCH net 1/2] net: tun: avoid disabling NAPI twice

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Date:   Thu, 30 Jun 2022 12:27:02 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        syzbot <syzkaller@...glegroups.com>,
        Petar Penkov <ppenkov@...atrix.com>
Subject: Re: [PATCH net 1/2] net: tun: avoid disabling NAPI twice

On Wed, Jun 29, 2022 at 8:19 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> Eric reports that syzbot made short work out of my speculative
> fix. Indeed when queue gets detached its tfile->tun remains,
> so we would try to stop NAPI twice with a detach(), close()
> sequence.
>
> Alternative fix would be to move tun_napi_disable() to
> tun_detach_all() and let the NAPI run after the queue
> has been detached.
>
> Fixes: a8fc8cb5692a ("net: tun: stop NAPI when detaching queues")

Reviewed-by: Eric Dumazet <edumazet@...gle.com>

> Reported-by: syzbot <syzkaller@...glegroups.com>
> Reported-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
> ---
> Cc: Petar Penkov <ppenkov@...atrix.com>
> ---
> CC: ppenkov@...atrix.com
> ---
>  drivers/net/tun.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index e2eb35887394..259b2b84b2b3 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -640,7 +640,8 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
>         tun = rtnl_dereference(tfile->tun);
>
>         if (tun && clean) {
> -               tun_napi_disable(tfile);
> +               if (!tfile->detached)
> +                       tun_napi_disable(tfile);
>                 tun_napi_del(tfile);
>         }
>
> --
> 2.36.1
>