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From:   Cong Wang <xiyou.wangcong@gmail.com>
Date:   Sat, 25 Jul 2020 22:35:12 -0700
Message-ID: <CAM_iQpUFL7VdCKSgUa6N3pg7ijjZRu6-6UAs2oNosM-EzgXbaQ@mail.gmail.com>
Subject: Re: [PATCH v2] net: ipv6: fix use-after-free Read in __xfrm6_tunnel_spi_lookup
To:     B K Karthik <bkkarthik@pesu.pes.edu>
Cc:     Steffen Klassert <steffen.klassert@secunet.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Linux Kernel Network Developers <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        skhan@linuxfoundation.org,
        linux-kernel-mentees@lists.linuxfoundation.org
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On Sat, Jul 25, 2020 at 8:09 PM B K Karthik <bkkarthik@pesu.pes.edu> wrote:
> @@ -103,10 +103,10 @@ static int __xfrm6_tunnel_spi_check(struct net *net, u32 spi)
>  {
>         struct xfrm6_tunnel_net *xfrm6_tn = xfrm6_tunnel_pernet(net);
>         struct xfrm6_tunnel_spi *x6spi;
> -       int index = xfrm6_tunnel_spi_hash_byspi(spi);
> +       int index = xfrm6_tunnel_spi_hash_byaddr((const xfrm_address_t *)spi);
>
>         hlist_for_each_entry(x6spi,
> -                            &xfrm6_tn->spi_byspi[index],
> +                            &xfrm6_tn->spi_byaddr[index],
>                              list_byspi) {
>                 if (x6spi->spi == spi)

How did you convince yourself this is correct? This lookup is still
using spi. :)

More importantly, can you explain how UAF happens? Apparently
the syzbot stack traces you quote make no sense at all. I also
looked at other similar reports, none of them makes sense to me.

Thanks.