Re: [PATCH nf] netfilter/xt_u32: validate user space input

[Wander Lairson Costa]

+stable as I forgot to add it in the Cc section.

On Mon, Aug 28, 2023 at 10:21 AM Wander Lairson Costa <wander@xxxxxxxxxx> wrote:
>
> The xt_u32 module doesn't validate the fields in the xt_u32 structure.
> An attacker may take advantage of this to trigger an OOB read by setting
> the size fields with a value beyond the arrays boundaries.
>
> Add a checkentry function to validate the structure.
>
> This was originally reported by the ZDI project (ZDI-CAN-18408).
>
> Fixes: 1b50b8a371e9 ("[NETFILTER]: Add u32 match")
> Signed-off-by: Wander Lairson Costa <wander@xxxxxxxxxx>
> ---
>  net/netfilter/xt_u32.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>
> diff --git a/net/netfilter/xt_u32.c b/net/netfilter/xt_u32.c
> index 177b40d08098..117d4615d668 100644
> --- a/net/netfilter/xt_u32.c
> +++ b/net/netfilter/xt_u32.c
> @@ -96,11 +96,32 @@ static bool u32_mt(const struct sk_buff *skb, struct xt_action_param *par)
>         return ret ^ data->invert;
>  }
>
> +static int u32_mt_checkentry(const struct xt_mtchk_param *par)
> +{
> +       const struct xt_u32 *data = par->matchinfo;
> +       const struct xt_u32_test *ct;
> +       unsigned int i;
> +
> +       if (data->ntests > ARRAY_SIZE(data->tests))
> +               return -EINVAL;
> +
> +       for (i = 0; i < data->ntests; ++i) {
> +               ct = &data->tests[i];
> +
> +               if (ct->nnums > ARRAY_SIZE(ct->location) ||
> +                   ct->nvalues > ARRAY_SIZE(ct->value))
> +                       return -EINVAL;
> +       }
> +
> +       return 0;
> +}
> +
>  static struct xt_match xt_u32_mt_reg __read_mostly = {
>         .name       = "u32",
>         .revision   = 0,
>         .family     = NFPROTO_UNSPEC,
>         .match      = u32_mt,
> +       .checkentry = u32_mt_checkentry,
>         .matchsize  = sizeof(struct xt_u32),
>         .me         = THIS_MODULE,
>  };
> --
> 2.41.0
>