netlink: Allow ext_ack to carry non-error messages

The NLMSGERR API already carries data (eg, a cookie) on the success path.
Allow a message string to be returned as well.

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 767c84e..26ded42 100644 (file)
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2313,17 +2313,16 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
         * requests to cap the error message, and get extra error data if
         * requested.
         */
+       if (nlk_has_extack && extack && extack->_msg)
+               tlvlen += nla_total_size(strlen(extack->_msg) + 1);
+
        if (err) {
                if (!(nlk->flags & NETLINK_F_CAP_ACK))
                        payload += nlmsg_len(nlh);
                else
                        flags |= NLM_F_CAPPED;
-               if (nlk_has_extack && extack) {
-                       if (extack->_msg)
-                               tlvlen += nla_total_size(strlen(extack->_msg) + 1);
-                       if (extack->bad_attr)
-                               tlvlen += nla_total_size(sizeof(u32));
-               }
+               if (nlk_has_extack && extack && extack->bad_attr)
+                       tlvlen += nla_total_size(sizeof(u32));
        } else {
                flags |= NLM_F_CAPPED;
 
@@ -2348,10 +2347,11 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
        memcpy(&errmsg->msg, nlh, payload > sizeof(*errmsg) ? nlh->nlmsg_len : sizeof(*nlh));
 
        if (nlk_has_extack && extack) {
+               if (extack->_msg) {
+                       WARN_ON(nla_put_string(skb, NLMSGERR_ATTR_MSG,
+                                              extack->_msg));
+               }
                if (err) {
-                       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 +