bridge: fix RCU races with bridge port

The macro br_port_exists() is not enough protection when only
RCU is being used. There is a tiny race where other CPU has cleared port
handler hook, but is bridge port flag might still be set.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 4 deletions

diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
index 4a6a378c84e3..e3de0a428f5d 100644
--- a/net/bridge/br_netlink.c
+++ b/net/bridge/br_netlink.c
@@ -119,11 +119,13 @@ static int br_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
 
         idx = 0;
         for_each_netdev(net, dev) {
+                struct net_bridge_port *port = br_port_get(dev);
+
                 /* not a bridge port */
-                if (!br_port_exists(dev) || idx < cb->args[0])
+                if (!port || idx < cb->args[0])
                         goto skip;
 
-                if (br_fill_ifinfo(skb, br_port_get(dev),
+                if (br_fill_ifinfo(skb, port,
                                    NETLINK_CB(cb->skb).pid,
                                    cb->nlh->nlmsg_seq, RTM_NEWLINK,
                                    NLM_F_MULTI) < 0)
@@ -169,9 +171,9 @@ static int br_rtm_setlink(struct sk_buff *skb,  struct nlmsghdr *nlh, void *arg)
         if (!dev)
                 return -ENODEV;
 
-        if (!br_port_exists(dev))
-                return -EINVAL;
         p = br_port_get(dev);
+        if (!p)
+                return -EINVAL;
 
         /* if kernel STP is running, don't allow changes */
         if (p->br->stp_enabled == BR_KERNEL_STP)