Ipvlan should return an error when an address is already in use.

The ipvlan code already knows how to detect when a duplicate address is
about to be assigned to an ipvlan device.  However, that failure is not
propogated outward and leads to a silent failure.

Introduce a validation step at ip address creation time and allow device
drivers to register to validate the incoming ip addresses.  The ipvlan
code is the first consumer.  If it detects an address in use, we can
return an error to the user before beginning to commit the new ifa in
the networking code.

This can be especially useful if it is necessary to provision many
ipvlans in containers.  The provisioning software (or operator) can use
this to detect situations where an ip address is unexpectedly in use.

Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 33 insertions, 0 deletions

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index df14815a3b8c..a7dd088d5fc9 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -176,6 +176,7 @@ EXPORT_SYMBOL(__ip_dev_find);
 static void rtmsg_ifa(int event, struct in_ifaddr *, struct nlmsghdr *, u32);
 
 static BLOCKING_NOTIFIER_HEAD(inetaddr_chain);
+static BLOCKING_NOTIFIER_HEAD(inetaddr_validator_chain);
 static void inet_del_ifa(struct in_device *in_dev, struct in_ifaddr **ifap,
 			 int destroy);
 #ifdef CONFIG_SYSCTL
@@ -441,6 +442,8 @@ static int __inet_insert_ifa(struct in_ifaddr *ifa, struct nlmsghdr *nlh,
 {
 	struct in_device *in_dev = ifa->ifa_dev;
 	struct in_ifaddr *ifa1, **ifap, **last_primary;
+	struct in_validator_info ivi;
+	int ret;
 
 	ASSERT_RTNL();
 
@@ -471,6 +474,23 @@ static int __inet_insert_ifa(struct in_ifaddr *ifa, struct nlmsghdr *nlh,
 		}
 	}
 
+	/* Allow any devices that wish to register ifaddr validtors to weigh
+	 * in now, before changes are committed.  The rntl lock is serializing
+	 * access here, so the state should not change between a validator call
+	 * and a final notify on commit.  This isn't invoked on promotion under
+	 * the assumption that validators are checking the address itself, and
+	 * not the flags.
+	 */
+	ivi.ivi_addr = ifa->ifa_address;
+	ivi.ivi_dev = ifa->ifa_dev;
+	ret = blocking_notifier_call_chain(&inetaddr_validator_chain,
+					   NETDEV_UP, &ivi);
+	ret = notifier_to_errno(ret);
+	if (ret) {
+		inet_free_ifa(ifa);
+		return ret;
+	}
+
 	if (!(ifa->ifa_flags & IFA_F_SECONDARY)) {
 		prandom_seed((__force u32) ifa->ifa_local);
 		ifap = last_primary;
@@ -1356,6 +1376,19 @@ int unregister_inetaddr_notifier(struct notifier_block *nb)
 }
 EXPORT_SYMBOL(unregister_inetaddr_notifier);
 
+int register_inetaddr_validator_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&inetaddr_validator_chain, nb);
+}
+EXPORT_SYMBOL(register_inetaddr_validator_notifier);
+
+int unregister_inetaddr_validator_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&inetaddr_validator_chain,
+	    nb);
+}
+EXPORT_SYMBOL(unregister_inetaddr_validator_notifier);
+
 /* Rename ifa_labels for a device name change. Make some effort to preserve
  * existing alias numbering and to create unique labels if possible.
 */