bridge: Validate IFLA_BRIDGE_FLAGS attribute length

Payload is currently accessed blindly and may exceed valid message
boundaries.

Fixes: 407af32 ("bridge: Add netlink interface to configure vlans on bridge ports")
Cc: Vlad Yasevich <vyasevic@redhat.com>
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/rtnetlink.c

@@ -2798,6 +2798,9 @@ static int rtnl_bridge_setlink(struct sk_buff *skb, struct nlmsghdr *nlh)
 	if (br_spec) {
 		nla_for_each_nested(attr, br_spec, rem) {
 			if (nla_type(attr) == IFLA_BRIDGE_FLAGS) {
+				if (nla_len(attr) < sizeof(flags))
+					return -EINVAL;
+
 				have_flags = true;
 				flags = nla_get_u16(attr);
 				break;
@@ -2868,6 +2871,9 @@ static int rtnl_bridge_dellink(struct sk_buff *skb, struct nlmsghdr *nlh)
 	if (br_spec) {
 		nla_for_each_nested(attr, br_spec, rem) {
 			if (nla_type(attr) == IFLA_BRIDGE_FLAGS) {
+				if (nla_len(attr) < sizeof(flags))
+					return -EINVAL;
+
 				have_flags = true;
 				flags = nla_get_u16(attr);
 				break;