netlink: extended ACK reporting

Add the base infrastructure and UAPI for netlink extended ACK
reporting. All "manual" calls to netlink_ack() pass NULL for now and
thus don't get extended ACK reporting.

Big thanks goes to Pablo Neira Ayuso for not only bringing up the
whole topic at netconf (again) but also coming up with the nlattr
passing trick and various other ideas.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Reviewed-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 62 insertions, 9 deletions

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index fc232441cf23..c1564768000e 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1652,6 +1652,13 @@ static int netlink_setsockopt(struct socket *sock, int level, int optname,
 			nlk->flags &= ~NETLINK_F_CAP_ACK;
 		err = 0;
 		break;
+	case NETLINK_EXT_ACK:
+		if (val)
+			nlk->flags |= NETLINK_F_EXT_ACK;
+		else
+			nlk->flags &= ~NETLINK_F_EXT_ACK;
+		err = 0;
+		break;
 	default:
 		err = -ENOPROTOOPT;
 	}
@@ -1736,6 +1743,15 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
 			return -EFAULT;
 		err = 0;
 		break;
+	case NETLINK_EXT_ACK:
+		if (len < sizeof(int))
+			return -EINVAL;
+		len = sizeof(int);
+		val = nlk->flags & NETLINK_F_EXT_ACK ? 1 : 0;
+		if (put_user(len, optlen) || put_user(val, optval))
+			return -EFAULT;
+		err = 0;
+		break;
 	default:
 		err = -ENOPROTOOPT;
 	}
@@ -2267,21 +2283,40 @@ error_free:
 }
 EXPORT_SYMBOL(__netlink_dump_start);
 
-void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err)
+void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
+		 const struct netlink_ext_ack *extack)
 {
 	struct sk_buff *skb;
 	struct nlmsghdr *rep;
 	struct nlmsgerr *errmsg;
 	size_t payload = sizeof(*errmsg);
+	size_t tlvlen = 0;
 	struct netlink_sock *nlk = nlk_sk(NETLINK_CB(in_skb).sk);
+	unsigned int flags = 0;
 
 	/* Error messages get the original request appened, unless the user
-	 * requests to cap the error message.
+	 * requests to cap the error message, and get extra error data if
+	 * requested.
 	 */
-	if (!(nlk->flags & NETLINK_F_CAP_ACK) && err)
-		payload += nlmsg_len(nlh);
+	if (err) {
+		if (!(nlk->flags & NETLINK_F_CAP_ACK))
+			payload += nlmsg_len(nlh);
+		else
+			flags |= NLM_F_CAPPED;
+		if (nlk->flags & NETLINK_F_EXT_ACK && extack) {
+			if (extack->_msg)
+				tlvlen += nla_total_size(strlen(extack->_msg) + 1);
+			if (extack->bad_attr)
+				tlvlen += nla_total_size(sizeof(u32));
+		}
+	} else {
+		flags |= NLM_F_CAPPED;
+	}
 
-	skb = nlmsg_new(payload, GFP_KERNEL);
+	if (tlvlen)
+		flags |= NLM_F_ACK_TLVS;
+
+	skb = nlmsg_new(payload + tlvlen, GFP_KERNEL);
 	if (!skb) {
 		struct sock *sk;
 
@@ -2297,17 +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);
+			  NLMSG_ERROR, payload, flags);
 	errmsg = nlmsg_data(rep);
 	errmsg->error = err;
 	memcpy(&errmsg->msg, nlh, payload > sizeof(*errmsg) ? 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));
+	}
+
+	nlmsg_end(skb, rep);
+
 	netlink_unicast(in_skb->sk, skb, NETLINK_CB(in_skb).portid, MSG_DONTWAIT);
 }
 EXPORT_SYMBOL(netlink_ack);
 
 int netlink_rcv_skb(struct sk_buff *skb, int (*cb)(struct sk_buff *,
-						     struct nlmsghdr *))
+						   struct nlmsghdr *,
+						   struct netlink_ext_ack *))
 {
+	struct netlink_ext_ack extack = {};
 	struct nlmsghdr *nlh;
 	int err;
 
@@ -2328,13 +2381,13 @@ int netlink_rcv_skb(struct sk_buff *skb, int (*cb)(struct sk_buff *,
 		if (nlh->nlmsg_type < NLMSG_MIN_TYPE)
 			goto ack;
 
-		err = cb(skb, nlh);
+		err = cb(skb, nlh, &extack);
 		if (err == -EINTR)
 			goto skip;
 
 ack:
 		if (nlh->nlmsg_flags & NLM_F_ACK || err)
-			netlink_ack(skb, nlh, err);
+			netlink_ack(skb, nlh, err, &extack);
 
 skip:
 		msglen = NLMSG_ALIGN(nlh->nlmsg_len);