netlink: bug fix: don't overrun skbs on vf_port dump

Noticed by Patrick McHardy: was continuing to fill skb after a
nla_put_failure, ignoring the size calculated by upper layer.  Now,
return -EMSGSIZE on any overruns, but also allow netdev to
fail ndo_get_vf_port with error other than -EMSGSIZE, thus unwinding
nest.

Signed-off-by: Scott Feldman <scofeldm@cisco.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 6 deletions

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 7ab86f3a1ea..7331bb2f6b9 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -722,14 +722,13 @@ static int rtnl_vf_ports_fill(struct sk_buff *skb, struct net_device *dev)
 
         for (vf = 0; vf < dev_num_vf(dev->dev.parent); vf++) {
                 vf_port = nla_nest_start(skb, IFLA_VF_PORT);
-                if (!vf_port) {
-                        nla_nest_cancel(skb, vf_ports);
-                        return -EMSGSIZE;
-                }
+                if (!vf_port)
+                        goto nla_put_failure;
                 NLA_PUT_U32(skb, IFLA_PORT_VF, vf);
                 err = dev->netdev_ops->ndo_get_vf_port(dev, vf, skb);
+                if (err == -EMSGSIZE)
+                        goto nla_put_failure;
                 if (err) {
-nla_put_failure:
                         nla_nest_cancel(skb, vf_port);
                         continue;
                 }
@@ -739,6 +738,10 @@ nla_put_failure:
         nla_nest_end(skb, vf_ports);
 
         return 0;
+
+nla_put_failure:
+        nla_nest_cancel(skb, vf_ports);
+        return -EMSGSIZE;
 }
 
 static int rtnl_port_self_fill(struct sk_buff *skb, struct net_device *dev)
@@ -753,7 +756,7 @@ static int rtnl_port_self_fill(struct sk_buff *skb, struct net_device *dev)
         err = dev->netdev_ops->ndo_get_vf_port(dev, PORT_SELF_VF, skb);
         if (err) {
                 nla_nest_cancel(skb, port_self);
-                return err;
+                return (err == -EMSGSIZE) ? err : 0;
         }
 
         nla_nest_end(skb, port_self);