netdev - Re: [PATCH net] net: sched: prevent a use after free

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Date:   Mon, 3 Feb 2020 12:33:30 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>, Jiri Pirko <jiri@...nulli.us>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Mohit Bhasi <mohitbhasi1998@...il.com>,
        "Mohit P. Tahiliani" <tahiliani@...k.edu.in>,
        "V. Saicharan" <vsaicharan1998@...il.com>,
        Gautam Ramakrishnan <gautamramk@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH net] net: sched: prevent a use after free

On Mon, Feb 3, 2020 at 11:58 AM Cong Wang <xiyou.wangcong@...il.com> wrote:
>
> On Mon, Feb 3, 2020 at 12:39 AM Dan Carpenter <dan.carpenter@...cle.com> wrote:
> > Why is that better?
>
> Because it is designed to be used in this scenario,
> as it defers the free after RTNL unlock which is after
> sch_tree_unlock() too.

Just in case of misunderstanding: I am _not_ suggesting to
use rtnl_kfree_skbs() to workaround this use-after-free,
rtnl_kfree_skbs() still has to be called after qdisc_pkt_len(),
at least for readability, despite that it could indeed
workaround the bug.

Thanks.