net: ipv4: ipmr: perform strict checks also for doit handlers

Make RTM_GETROUTE's doit handler use strict checks when
NETLINK_F_STRICT_CHK is set.

v2: - improve extack messages (DaveA).
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ipmr.c

@@ -2467,6 +2467,61 @@ static void igmpmsg_netlink_event(struct mr_table *mrt, struct sk_buff *pkt)
 	rtnl_set_sk_err(net, RTNLGRP_IPV4_MROUTE_R, -ENOBUFS);
 }
 
+static int ipmr_rtm_valid_getroute_req(struct sk_buff *skb,
+				       const struct nlmsghdr *nlh,
+				       struct nlattr **tb,
+				       struct netlink_ext_ack *extack)
+{
+	struct rtmsg *rtm;
+	int i, err;
+
+	if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*rtm))) {
+		NL_SET_ERR_MSG(extack, "ipv4: Invalid header for multicast route get request");
+		return -EINVAL;
+	}
+
+	if (!netlink_strict_get_check(skb))
+		return nlmsg_parse(nlh, sizeof(*rtm), tb, RTA_MAX,
+				   rtm_ipv4_policy, extack);
+
+	rtm = nlmsg_data(nlh);
+	if ((rtm->rtm_src_len && rtm->rtm_src_len != 32) ||
+	    (rtm->rtm_dst_len && rtm->rtm_dst_len != 32) ||
+	    rtm->rtm_tos || rtm->rtm_table || rtm->rtm_protocol ||
+	    rtm->rtm_scope || rtm->rtm_type || rtm->rtm_flags) {
+		NL_SET_ERR_MSG(extack, "ipv4: Invalid values in header for multicast route get request");
+		return -EINVAL;
+	}
+
+	err = nlmsg_parse_strict(nlh, sizeof(*rtm), tb, RTA_MAX,
+				 rtm_ipv4_policy, extack);
+	if (err)
+		return err;
+
+	if ((tb[RTA_SRC] && !rtm->rtm_src_len) ||
+	    (tb[RTA_DST] && !rtm->rtm_dst_len)) {
+		NL_SET_ERR_MSG(extack, "ipv4: rtm_src_len and rtm_dst_len must be 32 for IPv4");
+		return -EINVAL;
+	}
+
+	for (i = 0; i <= RTA_MAX; i++) {
+		if (!tb[i])
+			continue;
+
+		switch (i) {
+		case RTA_SRC:
+		case RTA_DST:
+		case RTA_TABLE:
+			break;
+		default:
+			NL_SET_ERR_MSG(extack, "ipv4: Unsupported attribute in multicast route get request");
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
 static int ipmr_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 			     struct netlink_ext_ack *extack)
 {
@@ -2475,18 +2530,14 @@ static int ipmr_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 	struct sk_buff *skb = NULL;
 	struct mfc_cache *cache;
 	struct mr_table *mrt;
-	struct rtmsg *rtm;
 	__be32 src, grp;
 	u32 tableid;
 	int err;
 
-	err = nlmsg_parse(nlh, sizeof(*rtm), tb, RTA_MAX,
-			  rtm_ipv4_policy, extack);
+	err = ipmr_rtm_valid_getroute_req(in_skb, nlh, tb, extack);
 	if (err < 0)
 		goto errout;
 
-	rtm = nlmsg_data(nlh);
-
 	src = tb[RTA_SRC] ? nla_get_in_addr(tb[RTA_SRC]) : 0;
 	grp = tb[RTA_DST] ? nla_get_in_addr(tb[RTA_DST]) : 0;
 	tableid = tb[RTA_TABLE] ? nla_get_u32(tb[RTA_TABLE]) : 0;