netdev - Re: [PATCH net] net: sched: fix use-after-free in tc_new

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Message-ID: <ygnhtudjofyg.fsf@nvidia.com>
Date:   Mon, 31 Jan 2022 21:36:23 +0200
From:   Vlad Buslov <vladbu@...dia.com>
To:     Eric Dumazet <edumazet@...gle.com>
CC:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Vlad Buslov <vladbu@...lanox.com>,
        Jiri Pirko <jiri@...lanox.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH net] net: sched: fix use-after-free in tc_new_tfilter()

On Mon 31 Jan 2022 at 21:31, Eric Dumazet <edumazet@...gle.com> wrote:
> On Mon, Jan 31, 2022 at 11:28 AM Vlad Buslov <vladbu@...dia.com> wrote:
>>
>> Yeah, but I also didn't get how the "chain" variable can get reused in
>> that other function (tcf_new_tfilter()). It seems to always be
>> unconditionally assigned with return value of tcf_chain_get().
>>
>
> This is why I removed the chain=NULL initialization which is not needed.
>
> The potential issue about replay was really about @q variable.

Got it. Initially it wasn't clear because I got the impression from
commit message that reuse of both variables can lead to use-after-free:
"we need to make sure @q and @chain local variables are cleared again,
or risk use-after-free".