netdev - Re: KASAN: use-after-free Read in cipso_v4

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Date:   Tue, 2 Mar 2021 19:13:23 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzbot <syzbot+9ec037722d2603a9f52e@...kaller.appspotmail.com>,
        David Miller <davem@...emloft.net>, dsahern@...nel.org,
        Jakub Kicinski <kuba@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>
Subject: Re: KASAN: use-after-free Read in cipso_v4_genopt

On Tue, Mar 2, 2021 at 2:15 PM Dmitry Vyukov <dvyukov@...gle.com> wrote:

...

> Not sure if it's the root cause or not, but I am looking at this
> reference drop in cipso_v4_doi_remove:
> https://elixir.bootlin.com/linux/v5.12-rc1/source/net/ipv4/cipso_ipv4.c#L522
> The thing is that it does not remove from the list if reference is not
> 0, right? So what if I send 1000 of netlink remove messages? Will it
> drain refcount to 0?
> I did not read all involved code, but the typical pattern is to drop
> refcount and always remove from the list. Then the last use will
> delete the object.
> Does it make any sense?

Looking at it quickly, the logic above seems sane.  I wrote this code
a *long* time ago, so let me get my head back into it and make sure
that still holds.

-- 
paul moore
www.paul-moore.com