Re: [PATCH v2] net: ipv6: fix use-after-free Read in __xfrm6_tunnel_spi_lookup

[Cong Wang]

On Sat, Jul 25, 2020 at 8:09 PM B K Karthik <bkkarthik@xxxxxxxxxxxx> 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.