rtnetlink: require unique netns identifier

Web:        https://git.kernel.org/torvalds/c/4ff66cae7f10b65b028dc3bdaaad9cc2989ef6ae
Commit:     4ff66cae7f10b65b028dc3bdaaad9cc2989ef6ae
Parent:     762c330d670e3d4b795cf7a8d761866fdd1eef49
Refname:    refs/heads/master
Author:     Christian Brauner <[email protected]>
AuthorDate: Wed Feb 7 13:53:20 2018 +0100
Committer:  David S. Miller <[email protected]>
CommitDate: Thu Feb 8 14:33:20 2018 -0500

    rtnetlink: require unique netns identifier
    
    Since we've added support for IFLA_IF_NETNSID for RTM_{DEL,GET,SET,NEW}LINK
    it is possible for userspace to send us requests with three different
    properties to identify a target network namespace. This affects at least
    RTM_{NEW,SET}LINK. Each of them could potentially refer to a different
    network namespace which is confusing. For legacy reasons the kernel will
    pick the IFLA_NET_NS_PID property first and then look for the
    IFLA_NET_NS_FD property but there is no reason to extend this type of
    behavior to network namespace ids. The regression potential is quite
    minimal since the rtnetlink requests in question either won't allow
    IFLA_IF_NETNSID requests before 4.16 is out (RTM_{NEW,SET}LINK) or don't
    support IFLA_NET_NS_{PID,FD} (RTM_{DEL,GET}LINK) in the first place.
    
    Signed-off-by: Christian Brauner <[email protected]>
    Acked-by: Jiri Benc <[email protected]>
    Signed-off-by: David S. Miller <[email protected]>
---
 net/core/rtnetlink.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 56af8e41abfc..bc290413a49d 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1951,6 +1951,38 @@ static struct net *rtnl_link_get_net_capable(const struct sk_buff *skb,
 	return net;
 }
 
+/* Verify that rtnetlink requests do not pass additional properties
+ * potentially referring to different network namespaces.
+ */
+static int rtnl_ensure_unique_netns(struct nlattr *tb[],
+				    struct netlink_ext_ack *extack,
+				    bool netns_id_only)
+{
+
+	if (netns_id_only) {
+		if (!tb[IFLA_NET_NS_PID] && !tb[IFLA_NET_NS_FD])
+			return 0;
+
+		NL_SET_ERR_MSG(extack, "specified netns attribute not supported");
+		return -EOPNOTSUPP;
+	}
+
+	if (tb[IFLA_IF_NETNSID] && (tb[IFLA_NET_NS_PID] || tb[IFLA_NET_NS_FD]))
+		goto invalid_attr;
+
+	if (tb[IFLA_NET_NS_PID] && (tb[IFLA_IF_NETNSID] || tb[IFLA_NET_NS_FD]))
+		goto invalid_attr;
+
+	if (tb[IFLA_NET_NS_FD] && (tb[IFLA_IF_NETNSID] || tb[IFLA_NET_NS_PID]))
+		goto invalid_attr;
+
+	return 0;
+
+invalid_attr:
+	NL_SET_ERR_MSG(extack, "multiple netns identifying attributes specified");
+	return -EINVAL;
+}
+
 static int validate_linkmsg(struct net_device *dev, struct nlattr *tb[])
 {
 	if (dev) {
@@ -2553,6 +2585,10 @@ static int rtnl_setlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 	if (err < 0)
 		goto errout;
 
+	err = rtnl_ensure_unique_netns(tb, extack, false);
+	if (err < 0)
+		goto errout;
+
 	if (tb[IFLA_IFNAME])
 		nla_strlcpy(ifname, tb[IFLA_IFNAME], IFNAMSIZ);
 	else
@@ -2649,6 +2685,10 @@ static int rtnl_dellink(struct sk_buff *skb, struct nlmsghdr *nlh,
 	if (err < 0)
 		return err;
 
+	err = rtnl_ensure_unique_netns(tb, extack, true);
+	if (err < 0)
+		return err;
+
 	if (tb[IFLA_IFNAME])
 		nla_strlcpy(ifname, tb[IFLA_IFNAME], IFNAMSIZ);
 
@@ -2802,6 +2842,10 @@ replay:
 	if (err < 0)
 		return err;
 
+	err = rtnl_ensure_unique_netns(tb, extack, false);
+	if (err < 0)
+		return err;
+
 	if (tb[IFLA_IFNAME])
 		nla_strlcpy(ifname, tb[IFLA_IFNAME], IFNAMSIZ);
 	else
@@ -3045,6 +3089,10 @@ static int rtnl_getlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 	if (err < 0)
 		return err;
 
+	err = rtnl_ensure_unique_netns(tb, extack, true);
+	if (err < 0)
+		return err;
+
 	if (tb[IFLA_IF_NETNSID]) {
 		netnsid = nla_get_s32(tb[IFLA_IF_NETNSID]);
 		tgt_net = get_target_net(NETLINK_CB(skb).sk, netnsid);
--
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