netlink: allow extack cookie also for error messages

Commit ba0dc5f6e0 ("netlink: allow sending extended ACK with cookie on
success") introduced a cookie which can be sent to userspace as part of
extended ack message in the form of NLMSGERR_ATTR_COOKIE attribute.
Currently the cookie is ignored if error code is non-zero but there is
no technical reason for such limitation and it can be useful to provide
machine parseable information as part of an error message.

Include NLMSGERR_ATTR_COOKIE whenever the cookie has been set,
regardless of error code.

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netlink/af_netlink.c

@@ -2392,19 +2392,14 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
 	if (nlk_has_extack && extack && extack->_msg)
 		tlvlen += nla_total_size(strlen(extack->_msg) + 1);
 
-	if (err) {
-		if (!(nlk->flags & NETLINK_F_CAP_ACK))
+	if (err && !(nlk->flags & NETLINK_F_CAP_ACK))
 		payload += nlmsg_len(nlh);
 	else
 		flags |= NLM_F_CAPPED;
-		if (nlk_has_extack && extack && extack->bad_attr)
+	if (err && nlk_has_extack && extack && extack->bad_attr)
 		tlvlen += nla_total_size(sizeof(u32));
-	} else {
-		flags |= NLM_F_CAPPED;
-
 	if (nlk_has_extack && extack && extack->cookie_len)
 		tlvlen += nla_total_size(extack->cookie_len);
-	}
 
 	if (tlvlen)
 		flags |= NLM_F_ACK_TLVS;
@@ -2427,20 +2422,16 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
 			WARN_ON(nla_put_string(skb, NLMSGERR_ATTR_MSG,
 					       extack->_msg));
 		}
-		if (err) {
-			if (extack->bad_attr &&
+		if (err && 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 -
 					    (u8 *)nlh));
-		} else {
 		if (extack->cookie_len)
 			WARN_ON(nla_put(skb, NLMSGERR_ATTR_COOKIE,
-						extack->cookie_len,
-						extack->cookie));
-		}
+					extack->cookie_len, extack->cookie));
 	}
 
 	nlmsg_end(skb, rep);