On Mon, 31 Jul 2023 20:12:47 +0800 Lin Ma wrote:

In short, the very direct idea to fix such lengh-check-forgotten bug is
add nla_len() checks like

  if (nla_len(nla) < SOME_LEN)
    return -EINVAL;

However, this is tedious and just like Leon said: add another layer of
cabal knowledge. The better solution should leverage the nla_policy and
discard nlattr whose length is invalid when doing parsing. That is, we
should defined a nested_policy for the X above like

Hard no. Putting array index into attr type is an advanced case and the
parsing code has to be able to deal with low level netlink details.
Higher level API should remove the nla_for_each_nested() completely
which is rather hard to achieve here.

Nacked-by: Jakub Kicinski [off-list ref]