net/sched: act_pedit: Add size check for TCA_PEDIT_PARMS_EX

The attribute TCA_PEDIT_PARMS_EX is not be included in pedit_policy and
one malicious user could fake a TCA_PEDIT_PARMS_EX whose length is
smaller than the intended sizeof(struct tc_pedit). Hence, the
dereference in tcf_pedit_init() could access dirty heap data.

static int tcf_pedit_init(...)
{
  // ...
  pattr = tb[TCA_PEDIT_PARMS]; // TCA_PEDIT_PARMS is included
  if (!pattr)
    pattr = tb[TCA_PEDIT_PARMS_EX]; // but this is not

  // ...
  parm = nla_data(pattr);

  index = parm->index; // parm is able to be smaller than 4 bytes
                       // and this dereference gets dirty skb_buff
                       // data created in netlink_sendmsg
}

This commit adds TCA_PEDIT_PARMS_EX length in pedit_policy which avoid
the above case, just like the TCA_PEDIT_PARMS.

Fixes: 71d0ed70 ("net/act_pedit: Support using offset relative to the conventional network headers")
Signed-off-by: Lin Ma <linma@zju.edu.cn>
Reviewed-by: Pedro Tammela <pctammela@mojatatu.com>
Link: https://lore.kernel.org/r/20230703110842.590282-1-linma@zju.edu.cn


Signed-off-by: Paolo Abeni <pabeni@redhat.com>