[PATCH 4/5] net: ipv4: allow setting address on interface outside current namespace

[Jonas Bonn]

This patch allows an interface outside of the current namespace to be
selected when setting a new IPv4 address for a device.  This uses the
IFA_TARGET_NETNSID attribute to select the namespace in which to search
for the interface to act upon.

Signed-off-by: Jonas Bonn <jonas@xxxxxxxxxxx>
---
 net/ipv4/devinet.c | 56 +++++++++++++++++++++++++++++++++-------------
 1 file changed, 41 insertions(+), 15 deletions(-)

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index a4b5bd4d2c89..459fb39b4a56 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -813,22 +813,17 @@ static void set_ifa_lifetime(struct in_ifaddr *ifa, __u32 valid_lft,
 		ifa->ifa_cstamp = ifa->ifa_tstamp;
 }
 
-static struct in_ifaddr *rtm_to_ifaddr(struct net *net, struct nlmsghdr *nlh,
+static struct in_ifaddr *rtm_to_ifaddr(struct nlattr* tb[],
+					struct net *net, struct nlmsghdr *nlh,
 				       __u32 *pvalid_lft, __u32 *pprefered_lft,
 				       struct netlink_ext_ack *extack)
 {
-	struct nlattr *tb[IFA_MAX+1];
 	struct in_ifaddr *ifa;
 	struct ifaddrmsg *ifm;
 	struct net_device *dev;
 	struct in_device *in_dev;
 	int err;
 
-	err = nlmsg_parse_deprecated(nlh, sizeof(*ifm), tb, IFA_MAX,
-				     ifa_ipv4_policy, extack);
-	if (err < 0)
-		goto errout;
-
 	ifm = nlmsg_data(nlh);
 	err = -EINVAL;
 	if (ifm->ifa_prefixlen > 32 || !tb[IFA_LOCAL])
@@ -922,16 +917,37 @@ static int inet_rtm_newaddr(struct sk_buff *skb, struct nlmsghdr *nlh,
 			    struct netlink_ext_ack *extack)
 {
 	struct net *net = sock_net(skb->sk);
+	struct net *tgt_net = NULL;
 	struct in_ifaddr *ifa;
 	struct in_ifaddr *ifa_existing;
 	__u32 valid_lft = INFINITY_LIFE_TIME;
 	__u32 prefered_lft = INFINITY_LIFE_TIME;
+	struct nlattr *tb[IFA_MAX+1];
+	int err;
 
 	ASSERT_RTNL();
 
-	ifa = rtm_to_ifaddr(net, nlh, &valid_lft, &prefered_lft, extack);
-	if (IS_ERR(ifa))
-		return PTR_ERR(ifa);
+	err = nlmsg_parse_deprecated(nlh, sizeof(struct ifaddrmsg), tb, IFA_MAX,
+				     ifa_ipv4_policy, extack);
+	if (err < 0)
+		return err;
+
+	if (tb[IFA_TARGET_NETNSID]) {
+		int32_t netnsid = nla_get_s32(tb[IFA_TARGET_NETNSID]);
+
+		tgt_net = rtnl_get_net_ns_capable(NETLINK_CB(skb).sk, netnsid);
+		if (IS_ERR(net)) {
+			NL_SET_ERR_MSG(extack, "ipv4: Invalid target network namespace id");
+			return PTR_ERR(net);
+		}
+		net = tgt_net;
+	}
+
+	ifa = rtm_to_ifaddr(tb, net, nlh, &valid_lft, &prefered_lft, extack);
+	if (IS_ERR(ifa)) {
+		err = PTR_ERR(ifa);
+		goto out;
+	}
 
 	ifa_existing = find_matching_ifa(ifa);
 	if (!ifa_existing) {
@@ -945,10 +961,11 @@ static int inet_rtm_newaddr(struct sk_buff *skb, struct nlmsghdr *nlh,
 
 			if (ret < 0) {
 				inet_free_ifa(ifa);
-				return ret;
+				err = ret;
+				goto out;
 			}
 		}
-		return __inet_insert_ifa(ifa, nlh, NETLINK_CB(skb).portid,
+		err = __inet_insert_ifa(ifa, nlh, NETLINK_CB(skb).portid,
 					 extack);
 	} else {
 		u32 new_metric = ifa->ifa_rt_priority;
@@ -956,8 +973,10 @@ static int inet_rtm_newaddr(struct sk_buff *skb, struct nlmsghdr *nlh,
 		inet_free_ifa(ifa);
 
 		if (nlh->nlmsg_flags & NLM_F_EXCL ||
-		    !(nlh->nlmsg_flags & NLM_F_REPLACE))
-			return -EEXIST;
+		    !(nlh->nlmsg_flags & NLM_F_REPLACE)) {
+			err = -EEXIST;
+			goto out;
+		}
 		ifa = ifa_existing;
 
 		if (ifa->ifa_rt_priority != new_metric) {
@@ -971,7 +990,14 @@ static int inet_rtm_newaddr(struct sk_buff *skb, struct nlmsghdr *nlh,
 				&check_lifetime_work, 0);
 		rtmsg_ifa(RTM_NEWADDR, ifa, nlh, NETLINK_CB(skb).portid);
 	}
-	return 0;
+
+	err = 0;
+
+out:
+	if (tgt_net)
+		put_net(tgt_net);
+
+	return err;
 }
 
 /*
-- 
2.20.1