linux-kernel - Re: [PATCH v2] net: ipv6: fix use-after-free Read in __xfrm6_tunnel_spi

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Message-ID: <20200727095043.GA20687@gauss3.secunet.de>
Date:   Mon, 27 Jul 2020 11:50:43 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
CC:     B K Karthik <bkkarthik@...u.pes.edu>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>,
        "Linux Kernel Network Developers" <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        <skhan@...uxfoundation.org>,
        <linux-kernel-mentees@...ts.linuxfoundation.org>
Subject: Re: [PATCH v2] net: ipv6: fix use-after-free Read in
 __xfrm6_tunnel_spi_lookup

On Sat, Jul 25, 2020 at 10:35:12PM -0700, Cong Wang wrote:
> On Sat, Jul 25, 2020 at 8:09 PM B K Karthik <bkkarthik@...u.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. :)

This can not be correct, it takes a u32 spi value and casts it to a
pointer to an IP address.