Re: [PATCH net-next 3/8] net: bridge: vlan: add rtm definitions and dump support

On 14/01/2020 18:49, David Ahern wrote:

On 1/14/20 9:45 AM, Nikolay Aleksandrov wrote:

quoted

On 14/01/2020 18:36, Nikolay Aleksandrov wrote:

quoted

On 14/01/2020 17:34, David Ahern wrote:

quoted

On 1/14/20 6:55 AM, Jakub Kicinski wrote:

quoted

On Mon, 13 Jan 2020 17:52:28 +0200, Nikolay Aleksandrov wrote:

quoted

+static int br_vlan_rtm_dump(struct sk_buff *skb, struct netlink_callback *cb)
+{
+	int idx = 0, err = 0, s_idx = cb->args[0];
+	struct net *net = sock_net(skb->sk);
+	struct br_vlan_msg *bvm;
+	struct net_device *dev;
+
+	if (cb->nlh->nlmsg_len < nlmsg_msg_size(sizeof(*bvm))) {

I wonder if it'd be useful to make this a strict != check? At least
when strict validation is on? Perhaps we'll one day want to extend 
the request?

+1. All new code should be using the strict checks.

IIRC, I did it to be able to add filter attributes later, but it should just use nlmsg_parse()
instead and all will be taken care of.
I'll respin v2 with that change.

Thanks,
 Nik

Actually nlmsg_parse() uses the same "<" check for the size before parsing. :)
If I change to it and with no attributes to parse would be essentially equal to the
current situation, but if I make it strict "!=" then we won't be able to add
filter attributes later as we won't be backwards compatible. I'll continue looking
into it, but IMO we should leave it as it is in order to be able to add the filtering later.

Thoughts ?

If the header is > sizeof(*bvm) I expect this part of
__nla_validate_parse() to kick in:

        if (unlikely(rem > 0)) {
                pr_warn_ratelimited("netlink: %d bytes leftover after
parsing attributes in process `%s'.\n",
                                    rem, current->comm);
                NL_SET_ERR_MSG(extack, "bytes leftover after parsing
attributes");
                if (validate & NL_VALIDATE_TRAILING)
                        return -EINVAL;
        }

Ah fair enough, so nlmsg_parse() would be better even without attrs.