Subject: [PATCH net-next 08/20] rtnetlink: Update rtnl_dump_ifinfo for strict data checking

From: David Ahern <[email-masked]>
Date: Thu, 4 Oct 2018 14:33:43 -0700

From: David Ahern <[email-masked]>

Update rtnl_dump_ifinfo for strict data checking. 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.

Existing code does not fail the dump if nlmsg_parse fails. That behavior
is kept for non-strict checking.

Signed-off-by: David Ahern <[email-masked]>
---
 net/core/rtnetlink.c | 97 +++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 69 insertions(+), 28 deletions(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index c3b434d724ea..4fd27b5db787 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1880,6 +1880,8 @@ 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;
 	struct net *net = sock_net(skb->sk);
 	struct net *tgt_net = net;
 	int h, s_h;
@@ -1892,44 +1894,84 @@ 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 (cb->strict_check) {
+		struct ifinfomsg *ifm;
 
-	if (nlmsg_parse(cb->nlh, hdrlen, tb, IFLA_MAX,
-			ifla_policy, cb->extack) >= 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))
-				return PTR_ERR(tgt_net);
+		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]);
+		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 (tb[IFLA_LINKINFO])
-			kind_ops = linkinfo_to_kind_ops(tb[IFLA_LINKINFO]);
+	err = nlmsg_parse(nlh, hdrlen, tb, IFLA_MAX, ifla_policy, extack);
+	if (err < 0) {
+		if (cb->strict_check)
+			return -EINVAL;
+		goto walk_entries;
+	}
 
-		if (master_idx || kind_ops)
-			flags |= NLM_F_DUMP_FILTERED;
+	for (i = 0; i <= IFLA_MAX; ++i) {
+		if (!tb[i])
+			continue;
+		switch (i) {
+		case IFLA_TARGET_NETNSID:
+			netnsid = nla_get_s32(tb[i]);
+			tgt_net = rtnl_get_net_ns_capable(skb->sk, netnsid);
+			if (IS_ERR(tgt_net)) {
+				NL_SET_ERR_MSG(extack, "Invalid target namespace id");
+				return PTR_ERR(tgt_net);
+			}
+			break;
+		case IFLA_EXT_MASK:
+			ext_filter_mask = nla_get_u32(tb[i]);
+			break;
+		case IFLA_MASTER:
+			master_idx = nla_get_u32(tb[i]);
+			break;
+		case IFLA_LINKINFO:
+			kind_ops = linkinfo_to_kind_ops(tb[i]);
+			break;
+		default:
+			if (cb->strict_check) {
+				NL_SET_ERR_MSG(extack, "Unsupported attribute in dump request");
+				return -EINVAL;
+			}
+		}
 	}
 
+	if (master_idx || kind_ops)
+		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];
@@ -1941,8 +1983,7 @@ 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