Subject: [PATCH RFC v2 net-next 06/25] rtnetlink: Update rtnl_dump_ifinfo to support NLM_F_DUMP_PROPER_HDR

From: David Ahern <[email-masked]>
Date: Mon, 1 Oct 2018 17:28:32 -0700

From: David Ahern <[email-masked]>

Update rtnl_dump_ifinfo to check for NLM_F_DUMP_PROPER_HDR in the netlink
message header. If the flag is set, the dump request is expected to have
an ifinfomsg struct as the header potentially followed by one or more
attributes. Any data passed in the header or as an attribute is taken as
a request to influence the data returned. Only values supported by the
dump handler are allowed to be non-0 or set in the request. At the moment
only the IFA_TARGET_NETNSID, IFLA_EXT_MASK, IFLA_MASTER, and IFLA_LINKINFO
attributes are supported.

Signed-off-by: David Ahern <[email-masked]>
---
 net/core/rtnetlink.c | 106 ++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 75 insertions(+), 31 deletions(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index da91b38297d3..2bf4b9916ca2 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1880,6 +1880,9 @@ EXPORT_SYMBOL_GPL(rtnl_get_net_ns_capable);
 
 static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
 {
+	struct netlink_ext_ack *extack = cb->extack;
+	const struct nlmsghdr *nlh = cb->nlh;
+	bool proper_hdr = !!(nlh->nlmsg_flags & NLM_F_DUMP_PROPER_HDR);
 	struct net *net = sock_net(skb->sk);
 	struct net *tgt_net = net;
 	int h, s_h;
@@ -1892,46 +1895,88 @@ static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
 	unsigned int flags = NLM_F_MULTI;
 	int master_idx = 0;
 	int netnsid = -1;
-	int err;
+	int err, i;
 	int hdrlen;
 
 	s_h = cb->args[0];
 	s_idx = cb->args[1];
 
-	/* A hack to preserve kernel<->userspace interface.
-	 * The correct header is ifinfomsg. It is consistent with rtnl_getlink.
-	 * However, before Linux v3.9 the code here assumed rtgenmsg and that's
-	 * what iproute2 < v3.9.0 used.
-	 * We can detect the old iproute2. Even including the IFLA_EXT_MASK
-	 * attribute, its netlink message is shorter than struct ifinfomsg.
-	 */
-	hdrlen = nlmsg_len(cb->nlh) < sizeof(struct ifinfomsg) ?
-		 sizeof(struct rtgenmsg) : sizeof(struct ifinfomsg);
+	if (proper_hdr) {
+		struct ifinfomsg *ifm;
 
-	if (nlmsg_parse(cb->nlh, hdrlen, tb, IFLA_MAX,
-			ifla_policy, NULL) >= 0) {
-		if (tb[IFLA_TARGET_NETNSID]) {
-			netnsid = nla_get_s32(tb[IFLA_TARGET_NETNSID]);
-			tgt_net = rtnl_get_net_ns_capable(skb->sk, netnsid);
-			if (IS_ERR(tgt_net)) {
-				tgt_net = net;
-				netnsid = -1;
-			}
+		hdrlen = sizeof(*ifm);
+		if (nlh->nlmsg_len < nlmsg_msg_size(hdrlen)) {
+			NL_SET_ERR_MSG(extack, "Invalid header");
+			return -EINVAL;
 		}
 
-		if (tb[IFLA_EXT_MASK])
-			ext_filter_mask = nla_get_u32(tb[IFLA_EXT_MASK]);
-
-		if (tb[IFLA_MASTER])
-			master_idx = nla_get_u32(tb[IFLA_MASTER]);
-
-		if (tb[IFLA_LINKINFO])
-			kind_ops = linkinfo_to_kind_ops(tb[IFLA_LINKINFO]);
+		ifm = nlmsg_data(nlh);
+		if (ifm->__ifi_pad || ifm->ifi_type || ifm->ifi_flags ||
+		    ifm->ifi_change) {
+			NL_SET_ERR_MSG(extack, "Invalid values in header for dump request");
+			return -EINVAL;
+		}
+		if (ifm->ifi_index) {
+			NL_SET_ERR_MSG(extack, "Filter by device index not supported");
+			return -EINVAL;
+		}
+	} else {
+		/* A hack to preserve kernel<->userspace interface.
+		 * The correct header is ifinfomsg. It is consistent with
+		 * rtnl_getlink. However, before Linux v3.9 the code here
+		 * assumed rtgenmsg and that's what iproute2 < v3.9.0 used.
+		 * We can detect the old iproute2. Even including the
+		 * IFLA_EXT_MASK attribute, its netlink message is shorter
+		 * than struct ifinfomsg.
+		 */
+		hdrlen = nlmsg_len(nlh) < sizeof(struct ifinfomsg) ?
+			 sizeof(struct rtgenmsg) : sizeof(struct ifinfomsg);
+	}
 
-		if (master_idx || kind_ops)
-			flags |= NLM_F_DUMP_FILTERED;
+	err = nlmsg_parse(nlh, hdrlen, tb, IFLA_MAX, ifla_policy, extack);
+	if (err < 0) {
+		if (proper_hdr) {
+			NL_SET_ERR_MSG(extack, "Failed to parse link attributes");
+			return -EINVAL;
+		}
+		goto walk_entries;
+	}
+
+	for (i = 0; i <= IFLA_MAX; ++i) {
+		switch (i) {
+		case IFLA_TARGET_NETNSID:
+			if (tb[i]) {
+				netnsid = nla_get_s32(tb[i]);
+				tgt_net = rtnl_get_net_ns_capable(skb->sk,
+								  netnsid);
+				if (IS_ERR(tgt_net))
+					return PTR_ERR(tgt_net);
+			}
+			break;
+		case IFLA_EXT_MASK:
+			if (tb[i])
+				ext_filter_mask = nla_get_u32(tb[i]);
+			break;
+		case IFLA_MASTER:
+			if (tb[i])
+				master_idx = nla_get_u32(tb[i]);
+			break;
+		case IFLA_LINKINFO:
+			if (tb[i])
+				kind_ops = linkinfo_to_kind_ops(tb[i]);
+			break;
+		default:
+			if (proper_hdr && tb[i]) {
+				NL_SET_ERR_MSG(extack, "Unsupported attribute in dump request");
+				return -EINVAL;
+			}
+		}
 	}
 
+	if (master_idx || kind_ops || netnsid >= 0)
+		flags |= NLM_F_DUMP_FILTERED;
+
+walk_entries:
 	for (h = s_h; h < NETDEV_HASHENTRIES; h++, s_idx = 0) {
 		idx = 0;
 		head = &tgt_net->dev_index_head[h];
@@ -1943,8 +1988,7 @@ static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
 			err = rtnl_fill_ifinfo(skb, dev, net,
 					       RTM_NEWLINK,
 					       NETLINK_CB(cb->skb).portid,
-					       cb->nlh->nlmsg_seq, 0,
-					       flags,
+					       nlh->nlmsg_seq, 0, flags,
 					       ext_filter_mask, 0, NULL, 0,
 					       netnsid);
 
-- 
2.11.0