netlink: add nested array policy validation

Sometimes nested netlink attributes are just used as arrays, with
the nla_type() of each not being used; we have this in nl80211 and
e.g. NFTA_SET_ELEM_LIST_ELEMENTS.

Add the ability to validate this type of message directly in the
policy, by adding the type NLA_NESTED_ARRAY which does exactly
this: require a first level of nesting but ignore the attribute
type, and then inside each require a second level of nested and
validate those attributes against a given policy (if present).

Note that some nested array types actually require that all of
the entries have the same index, this is possible to express in
a nested policy already, apart from the validation that only the
one allowed type is used.

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

1 files changed, 51 insertions, 0 deletions

diff --git a/lib/nlattr.c b/lib/nlattr.c
index 04750f88477c..2f8feff669a7 100644
--- a/lib/nlattr.c
+++ b/lib/nlattr.c
@@ -67,6 +67,34 @@ static int validate_nla_bitfield32(const struct nlattr *nla,
 	return 0;
 }
 
+static int nla_validate_array(const struct nlattr *head, int len, int maxtype,
+			      const struct nla_policy *policy,
+			      struct netlink_ext_ack *extack)
+{
+	const struct nlattr *entry;
+	int rem;
+
+	nla_for_each_attr(entry, head, len, rem) {
+		int ret;
+
+		if (nla_len(entry) == 0)
+			continue;
+
+		if (nla_len(entry) < NLA_HDRLEN) {
+			NL_SET_ERR_MSG_ATTR(extack, entry,
+					    "Array element too short");
+			return -ERANGE;
+		}
+
+		ret = nla_validate(nla_data(entry), nla_len(entry),
+				   maxtype, policy, extack);
+		if (ret < 0)
+			return ret;
+	}
+
+	return 0;
+}
+
 static int validate_nla(const struct nlattr *nla, int maxtype,
 			const struct nla_policy *policy,
 			struct netlink_ext_ack *extack)
@@ -169,6 +197,29 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
 			}
 		}
 		break;
+	case NLA_NESTED_ARRAY:
+		/* a nested array attribute is allowed to be empty; if its not,
+		 * it must have a size of at least NLA_HDRLEN.
+		 */
+		if (attrlen == 0)
+			break;
+		if (attrlen < NLA_HDRLEN)
+			goto out_err;
+		if (pt->validation_data) {
+			int err;
+
+			err = nla_validate_array(nla_data(nla), nla_len(nla),
+						 pt->len, pt->validation_data,
+						 extack);
+			if (err < 0) {
+				/*
+				 * return directly to preserve the inner
+				 * error message/attribute pointer
+				 */
+				return err;
+			}
+		}
+		break;
 	default:
 		if (pt->len)
 			minlen = pt->len;