netlink: add ethernet address policy types

Commonly, ethernet addresses are just using a policy of
	{ .len = ETH_ALEN }
which leaves userspace free to send more data than it should,
which may hide bugs.

Introduce NLA_EXACT_LEN which checks for exact size, rejecting
the attribute if it's not exactly that length. Also add
NLA_EXACT_LEN_WARN which requires the minimum length and will
warn on longer attributes, for backward compatibility.

Use these to define NLA_POLICY_ETH_ADDR (new strict policy) and
NLA_POLICY_ETH_ADDR_COMPAT (compatible policy with warning);
these are used like this:

    static const struct nla_policy <name>[...] = {
        [NL_ATTR_NAME] = NLA_POLICY_ETH_ADDR,
        ...
    };

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Reviewed-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 1 deletions

diff --git a/lib/nlattr.c b/lib/nlattr.c
index 36d74b079151..bb6fe5ed4ecf 100644
--- a/lib/nlattr.c
+++ b/lib/nlattr.c
@@ -82,12 +82,18 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
 
 	BUG_ON(pt->type > NLA_TYPE_MAX);
 
-	if (nla_attr_len[pt->type] && attrlen != nla_attr_len[pt->type]) {
+	if ((nla_attr_len[pt->type] && attrlen != nla_attr_len[pt->type]) ||
+	    (pt->type == NLA_EXACT_LEN_WARN && attrlen != pt->len)) {
 		pr_warn_ratelimited("netlink: '%s': attribute type %d has an invalid length.\n",
 				    current->comm, type);
 	}
 
 	switch (pt->type) {
+	case NLA_EXACT_LEN:
+		if (attrlen != pt->len)
+			return -ERANGE;
+		break;
+
 	case NLA_REJECT:
 		if (pt->validation_data && error_msg)
 			*error_msg = pt->validation_data;