From mboxrd@z Thu Jan  1 00:00:00 1970
From: Johannes Berg <johannes@sipsolutions.net>
Subject: Re: [PATCH v2 1/5] netlink: extended ACK reporting
Date: Mon, 10 Apr 2017 12:15:40 +0200
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Cc: pablo@netfilter.org, Jamal Hadi Salim <jhs@mojatatu.com>,
        Jiri Benc <jbenc@redhat.com>,
        David Ahern <dsa@cumulusnetworks.com>, jiri@resnulli.us
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> @@ -2300,14 +2332,35 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err)
        rep = __nlmsg_put(skb, NETLINK_CB(in_skb).portid, nlh->nlmsg_seq,
>  			  NLMSG_ERROR, payload, 0);
>  	errmsg = nlmsg_data(rep);
>  	errmsg->error = err;

This is still wrong - now the message length is too short.

At the very least,

> -	memcpy(&errmsg->msg, nlh, payload > sizeof(*errmsg) ? nlh-
> >nlmsg_len : sizeof(*nlh));
> +	memcpy(&errmsg->msg, nlh,
> +	       !(nlk->flags & NETLINK_F_CAP_ACK) ? nlh->nlmsg_len
> +						 : sizeof(*nlh));
> +
> +	if (err && nlk->flags & NETLINK_F_EXT_ACK && extack) {
> +		if (extack->_msg)
> +			WARN_ON(nla_put_string(skb,
> NLMSGERR_ATTR_MSG,
> +					       extack->_msg));
> +		if (extack->bad_attr &&
> +		    !WARN_ON((u8 *)extack->bad_attr < in_skb->data
> ||
> +			     (u8 *)extack->bad_attr >= in_skb->data
> +
> +						       in_skb->len))
> +			WARN_ON(nla_put_u32(skb, NLMSGERR_ATTR_OFFS,
> +					    (u8 *)extack->bad_attr -
> +					    in_skb->data));
> +		if (extack->missing_attr)
> +			WARN_ON(nla_put_u16(skb, NLMSGERR_ATTR_ATTR,
> +					    extack->missing_attr));
> +	}

I need to add
 rep->nlmsg_len = skb->len;

>  	netlink_unicast(in_skb->sk, skb, NETLINK_CB(in_skb).portid,
> MSG_DONTWAIT);

Here, but at that point I think it makes sense to rewrite this nlmsg
put stuff here as well.

johannes