> @@ -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

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