Merge branch 'ethtool-fail-with-error-if-request-has-unknown-flags'

Michal Kubecek says:

====================
ethtool: fail with error if request has unknown flags

Jakub Kicinski pointed out that if unrecognized flags are set in netlink
header request, kernel shoud fail with an error rather than silently
ignore them so that we have more freedom in future flags semantics.

To help userspace with handling such errors, inform the client which
flags are supported by kernel. For that purpose, we need to allow
passing cookies as part of extack also in case of error (they can be
only passed on success now).
====================

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index 205fa7b..4090524 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -119,6 +119,15 @@
 	extack->cookie_len = sizeof(__cookie);
 }
 
+static inline void nl_set_extack_cookie_u32(struct netlink_ext_ack *extack,
+					    u32 cookie)
+{
+	u32 __cookie = cookie;
+
+	memcpy(extack->cookie, &__cookie, sizeof(__cookie));
+	extack->cookie_len = sizeof(__cookie);
+}
+
 void netlink_kernel_release(struct sock *sk);
 int __netlink_change_ngroups(struct sock *sk, unsigned int groups);
 int netlink_change_ngroups(struct sock *sk, unsigned int groups);
diff --git a/net/ethtool/netlink.c b/net/ethtool/netlink.c
index 180c194..fc9e0b8 100644
--- a/net/ethtool/netlink.c
+++ b/net/ethtool/netlink.c
@@ -40,6 +40,7 @@
 	struct nlattr *tb[ETHTOOL_A_HEADER_MAX + 1];
 	const struct nlattr *devname_attr;
 	struct net_device *dev = NULL;
+	u32 flags = 0;
 	int ret;
 
 	if (!header) {
@@ -50,8 +51,17 @@
 			       ethnl_header_policy, extack);
 	if (ret < 0)
 		return ret;
-	devname_attr = tb[ETHTOOL_A_HEADER_DEV_NAME];
+	if (tb[ETHTOOL_A_HEADER_FLAGS]) {
+		flags = nla_get_u32(tb[ETHTOOL_A_HEADER_FLAGS]);
+		if (flags & ~ETHTOOL_FLAG_ALL) {
+			NL_SET_ERR_MSG_ATTR(extack, tb[ETHTOOL_A_HEADER_FLAGS],
+					    "unrecognized request flags");
+			nl_set_extack_cookie_u32(extack, ETHTOOL_FLAG_ALL);
+			return -EOPNOTSUPP;
+		}
+	}
 
+	devname_attr = tb[ETHTOOL_A_HEADER_DEV_NAME];
 	if (tb[ETHTOOL_A_HEADER_DEV_INDEX]) {
 		u32 ifindex = nla_get_u32(tb[ETHTOOL_A_HEADER_DEV_INDEX]);
 
@@ -90,9 +100,7 @@
 	}
 
 	req_info->dev = dev;
-	if (tb[ETHTOOL_A_HEADER_FLAGS])
-		req_info->flags = nla_get_u32(tb[ETHTOOL_A_HEADER_FLAGS]);
-
+	req_info->flags = flags;
 	return 0;
 }
 
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 5313f1c..2f23479 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2392,19 +2392,14 @@
 	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 && extack->bad_attr)
-			tlvlen += nla_total_size(sizeof(u32));
-	} else {
+	if (err && !(nlk->flags & NETLINK_F_CAP_ACK))
+		payload += nlmsg_len(nlh);
+	else
 		flags |= NLM_F_CAPPED;
-
-		if (nlk_has_extack && extack && extack->cookie_len)
-			tlvlen += nla_total_size(extack->cookie_len);
-	}
+	if (err && nlk_has_extack && extack && extack->bad_attr)
+		tlvlen += nla_total_size(sizeof(u32));
+	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 @@
 			WARN_ON(nla_put_string(skb, NLMSGERR_ATTR_MSG,
 					       extack->_msg));
 		}
-		if (err) {
-			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 -
-						    (u8 *)nlh));
-		} else {
-			if (extack->cookie_len)
-				WARN_ON(nla_put(skb, NLMSGERR_ATTR_COOKIE,
-						extack->cookie_len,
-						extack->cookie));
-		}
+		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));
+		if (extack->cookie_len)
+			WARN_ON(nla_put(skb, NLMSGERR_ATTR_COOKIE,
+					extack->cookie_len, extack->cookie));
 	}
 
 	nlmsg_end(skb, rep);