macvlan: better mode validation

macvlan passthrough mode is special: it's not possible to switch to or
from it through a netlink command.

But if you try, the command will succeed, which is
confusing.

Validate input and return error to user.

Cc:  Sridhar Samudrala <sri@us.ibm.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 14 insertions, 2 deletions

diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
index 18373b6ae37d..13937f9c04ad 100644
--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -863,6 +863,18 @@ static int macvlan_changelink(struct net_device *dev,
                 struct nlattr *tb[], struct nlattr *data[])
 {
         struct macvlan_dev *vlan = netdev_priv(dev);
+        enum macvlan_mode mode;
+        bool set_mode = false;
+
+        /* Validate mode, but don't set yet: setting flags may fail. */
+        if (data && data[IFLA_MACVLAN_MODE]) {
+                set_mode = true;
+                mode = nla_get_u32(data[IFLA_MACVLAN_MODE]);
+                /* Passthrough mode can't be set or cleared dynamically */
+                if ((mode == MACVLAN_MODE_PASSTHRU) !=
+                    (vlan->mode == MACVLAN_MODE_PASSTHRU))
+                        return -EINVAL;
+        }
 
         if (data && data[IFLA_MACVLAN_FLAGS]) {
                 __u16 flags = nla_get_u16(data[IFLA_MACVLAN_FLAGS]);
@@ -879,8 +891,8 @@ static int macvlan_changelink(struct net_device *dev,
                 }
                 vlan->flags = flags;
         }
-        if (data && data[IFLA_MACVLAN_MODE])
-                vlan->mode = nla_get_u32(data[IFLA_MACVLAN_MODE]);
+        if (set_mode)
+                vlan->mode = mode;
         return 0;
 }