netlink: introduce NLA_POLICY_MAX_BE

netlink allows to specify allowed ranges for integer types.
Unfortunately, nfnetlink passes integers in big endian, so the existing
NLA_POLICY_MAX() cannot be used.

At the moment, nfnetlink users, such as nf_tables, need to resort to
programmatic checking via helpers such as nft_parse_u32_check().

This is both cumbersome and error prone.  This adds NLA_POLICY_MAX_BE
which adds range check support for BE16, BE32 and BE64 integers.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/netlink.h

@@ -325,6 +325,7 @@ struct nla_policy {
 		struct netlink_range_validation_signed *range_signed;
 		struct {
 			s16 min, max;
+			u8 network_byte_order:1;
 		};
 		int (*validate)(const struct nlattr *attr,
 				struct netlink_ext_ack *extack);
@@ -418,6 +419,14 @@ struct nla_policy {
 	.type = NLA_ENSURE_INT_OR_BINARY_TYPE(tp),	\
 	.validation_type = NLA_VALIDATE_MAX,		\
 	.max = _max,					\
+	.network_byte_order = 0,			\
+}
+
+#define NLA_POLICY_MAX_BE(tp, _max) {			\
+	.type = NLA_ENSURE_UINT_TYPE(tp),		\
+	.validation_type = NLA_VALIDATE_MAX,		\
+	.max = _max,					\
+	.network_byte_order = 1,			\
 }
 
 #define NLA_POLICY_MASK(tp, _mask) {			\

lib/nlattr.c

@@ -159,6 +159,31 @@ void nla_get_range_unsigned(const struct nla_policy *pt,
 	}
 }
 
+static u64 nla_get_attr_bo(const struct nla_policy *pt,
+			   const struct nlattr *nla)
+{
+	switch (pt->type) {
+	case NLA_U16:
+		if (pt->network_byte_order)
+			return ntohs(nla_get_be16(nla));
+
+		return nla_get_u16(nla);
+	case NLA_U32:
+		if (pt->network_byte_order)
+			return ntohl(nla_get_be32(nla));
+
+		return nla_get_u32(nla);
+	case NLA_U64:
+		if (pt->network_byte_order)
+			return be64_to_cpu(nla_get_be64(nla));
+
+		return nla_get_u64(nla);
+	}
+
+	WARN_ON_ONCE(1);
+	return 0;
+}
+
 static int nla_validate_range_unsigned(const struct nla_policy *pt,
 				       const struct nlattr *nla,
 				       struct netlink_ext_ack *extack,
@@ -172,12 +197,10 @@ static int nla_validate_range_unsigned(const struct nla_policy *pt,
 		value = nla_get_u8(nla);
 		break;
 	case NLA_U16:
-		value = nla_get_u16(nla);
-		break;
 	case NLA_U32:
-		value = nla_get_u32(nla);
-		break;
 	case NLA_U64:
+		value = nla_get_attr_bo(pt, nla);
+		break;
 	case NLA_MSECS:
 		value = nla_get_u64(nla);
 		break;