net/sched: cls_route: make netlink errors meaningful

Use netlink extended ack and parsing policies to return more meaningful
errors instead of the relying solely on errnos.

Reviewed-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_route.c

@@ -375,9 +375,9 @@ static int route4_delete(struct tcf_proto *tp, void *arg, bool *last,
 
 static const struct nla_policy route4_policy[TCA_ROUTE4_MAX + 1] = {
 	[TCA_ROUTE4_CLASSID]	= { .type = NLA_U32 },
-	[TCA_ROUTE4_TO]		= { .type = NLA_U32 },
-	[TCA_ROUTE4_FROM]	= { .type = NLA_U32 },
-	[TCA_ROUTE4_IIF]	= { .type = NLA_U32 },
+	[TCA_ROUTE4_TO]		= NLA_POLICY_MAX(NLA_U32, 0xFF),
+	[TCA_ROUTE4_FROM]	= NLA_POLICY_MAX(NLA_U32, 0xFF),
+	[TCA_ROUTE4_IIF]	= NLA_POLICY_MAX(NLA_U32, 0x7FFF),
 };
 
 static int route4_set_parms(struct net *net, struct tcf_proto *tp,
@@ -397,33 +397,37 @@ static int route4_set_parms(struct net *net, struct tcf_proto *tp,
 		return err;
 
 	if (tb[TCA_ROUTE4_TO]) {
-		if (new && handle & 0x8000)
+		if (new && handle & 0x8000) {
+			NL_SET_ERR_MSG(extack, "Invalid handle");
 			return -EINVAL;
+		}
 		to = nla_get_u32(tb[TCA_ROUTE4_TO]);
-		if (to > 0xFF)
-			return -EINVAL;
 		nhandle = to;
 	}
 
+	if (tb[TCA_ROUTE4_FROM] && tb[TCA_ROUTE4_IIF]) {
+		NL_SET_ERR_MSG_ATTR(extack, tb[TCA_ROUTE4_FROM],
+				    "'from' and 'fromif' are mutually exclusive");
+		return -EINVAL;
+	}
+
 	if (tb[TCA_ROUTE4_FROM]) {
-		if (tb[TCA_ROUTE4_IIF])
-			return -EINVAL;
 		id = nla_get_u32(tb[TCA_ROUTE4_FROM]);
-		if (id > 0xFF)
-			return -EINVAL;
 		nhandle |= id << 16;
 	} else if (tb[TCA_ROUTE4_IIF]) {
 		id = nla_get_u32(tb[TCA_ROUTE4_IIF]);
-		if (id > 0x7FFF)
-			return -EINVAL;
 		nhandle |= (id | 0x8000) << 16;
 	} else
 		nhandle |= 0xFFFF << 16;
 
 	if (handle && new) {
 		nhandle |= handle & 0x7F00;
-		if (nhandle != handle)
+		if (nhandle != handle) {
+			NL_SET_ERR_MSG_FMT(extack,
+					   "Handle mismatch constructed: %x (expected: %x)",
+					   handle, nhandle);
 			return -EINVAL;
+		}
 	}
 
 	if (!nhandle) {
@@ -478,7 +482,6 @@ static int route4_change(struct net *net, struct sk_buff *in_skb,
 	struct route4_filter __rcu **fp;
 	struct route4_filter *fold, *f1, *pfp, *f = NULL;
 	struct route4_bucket *b;
-	struct nlattr *opt = tca[TCA_OPTIONS];
 	struct nlattr *tb[TCA_ROUTE4_MAX + 1];
 	unsigned int h, th;
 	int err;
@@ -489,10 +492,12 @@ static int route4_change(struct net *net, struct sk_buff *in_skb,
 		return -EINVAL;
 	}
 
-	if (opt == NULL)
+	if (NL_REQ_ATTR_CHECK(extack, NULL, tca, TCA_OPTIONS)) {
+		NL_SET_ERR_MSG_MOD(extack, "Missing options");
 		return -EINVAL;
+	}
 
-	err = nla_parse_nested_deprecated(tb, TCA_ROUTE4_MAX, opt,
+	err = nla_parse_nested_deprecated(tb, TCA_ROUTE4_MAX, tca[TCA_OPTIONS],
 					  route4_policy, NULL);
 	if (err < 0)
 		return err;