netlink: move extack setting into validate_nla()

This unifies the code between nla_parse() which sets the bad
attribute pointer and an error message, and nla_validate()
which only sets the bad attribute pointer.

It also cleans up the code for NLA_REJECT and paves the way
for nested policy validation, as it will allow us to easily
skip setting the "generic" message without any extra args
like the **error_msg now, just passing the extack through is
now enough.

While at it, remove the unnecessary label in nla_parse().
Suggested-by: NDavid Ahern <dsahern@gmail.com>
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

lib/nlattr.c

@@ -69,10 +69,11 @@ static int validate_nla_bitfield32(const struct nlattr *nla,
 
 static int validate_nla(const struct nlattr *nla, int maxtype,
 			const struct nla_policy *policy,
-			const char **error_msg)
+			struct netlink_ext_ack *extack)
 {
 	const struct nla_policy *pt;
 	int minlen = 0, attrlen = nla_len(nla), type = nla_type(nla);
+	int err = -ERANGE;
 
 	if (type <= 0 || type > maxtype)
 		return 0;
@@ -90,24 +91,31 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
 	switch (pt->type) {
 	case NLA_EXACT_LEN:
 		if (attrlen != pt->len)
-			return -ERANGE;
+			goto out_err;
 		break;
 
 	case NLA_REJECT:
-		if (pt->validation_data && error_msg)
-			*error_msg = pt->validation_data;
-		return -EINVAL;
+		if (extack && pt->validation_data) {
+			NL_SET_BAD_ATTR(extack, nla);
+			extack->_msg = pt->validation_data;
+			return -EINVAL;
+		}
+		err = -EINVAL;
+		goto out_err;
 
 	case NLA_FLAG:
 		if (attrlen > 0)
-			return -ERANGE;
+			goto out_err;
 		break;
 
 	case NLA_BITFIELD32:
 		if (attrlen != sizeof(struct nla_bitfield32))
-			return -ERANGE;
+			goto out_err;
 
-		return validate_nla_bitfield32(nla, pt->validation_data);
+		err = validate_nla_bitfield32(nla, pt->validation_data);
+		if (err)
+			goto out_err;
+		break;
 
 	case NLA_NUL_STRING:
 		if (pt->len)
@@ -115,13 +123,15 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
 		else
 			minlen = attrlen;
 
-		if (!minlen || memchr(nla_data(nla), '\0', minlen) == NULL)
-			return -EINVAL;
+		if (!minlen || memchr(nla_data(nla), '\0', minlen) == NULL) {
+			err = -EINVAL;
+			goto out_err;
+		}
 		/* fall through */
 
 	case NLA_STRING:
 		if (attrlen < 1)
-			return -ERANGE;
+			goto out_err;
 
 		if (pt->len) {
 			char *buf = nla_data(nla);
@@ -130,13 +140,13 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
 				attrlen--;
 
 			if (attrlen > pt->len)
-				return -ERANGE;
+				goto out_err;
 		}
 		break;
 
 	case NLA_BINARY:
 		if (pt->len && attrlen > pt->len)
-			return -ERANGE;
+			goto out_err;
 		break;
 
 	case NLA_NESTED:
@@ -152,10 +162,13 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
 			minlen = nla_attr_minlen[pt->type];
 
 		if (attrlen < minlen)
-			return -ERANGE;
+			goto out_err;
 	}
 
 	return 0;
+out_err:
+	NL_SET_ERR_MSG_ATTR(extack, nla, "Attribute failed policy validation");
+	return err;
 }
 
 /**
@@ -180,12 +193,10 @@ int nla_validate(const struct nlattr *head, int len, int maxtype,
 	int rem;
 
 	nla_for_each_attr(nla, head, len, rem) {
-		int err = validate_nla(nla, maxtype, policy, NULL);
+		int err = validate_nla(nla, maxtype, policy, extack);
 
-		if (err < 0) {
-			NL_SET_BAD_ATTR(extack, nla);
+		if (err < 0)
 			return err;
-		}
 	}
 
 	return 0;
@@ -241,7 +252,7 @@ int nla_parse(struct nlattr **tb, int maxtype, const struct nlattr *head,
 	      struct netlink_ext_ack *extack)
 {
 	const struct nlattr *nla;
-	int rem, err;
+	int rem;
 
 	memset(tb, 0, sizeof(struct nlattr *) * (maxtype + 1));
 
@@ -249,17 +260,12 @@ int nla_parse(struct nlattr **tb, int maxtype, const struct nlattr *head,
 		u16 type = nla_type(nla);
 
 		if (type > 0 && type <= maxtype) {
-			static const char _msg[] = "Attribute failed policy validation";
-			const char *msg = _msg;
-
 			if (policy) {
-				err = validate_nla(nla, maxtype, policy, &msg);
-				if (err < 0) {
-					NL_SET_BAD_ATTR(extack, nla);
-					if (extack)
-						extack->_msg = msg;
-					goto errout;
-				}
+				int err = validate_nla(nla, maxtype, policy,
+						       extack);
+
+				if (err < 0)
+					return err;
 			}
 
 			tb[type] = (struct nlattr *)nla;
@@ -270,9 +276,7 @@ int nla_parse(struct nlattr **tb, int maxtype, const struct nlattr *head,
 		pr_warn_ratelimited("netlink: %d bytes leftover after parsing attributes in process `%s'.\n",
 				    rem, current->comm);
 
-	err = 0;
-errout:
-	return err;
+	return 0;
 }
 EXPORT_SYMBOL(nla_parse);