net: bridge: fix ioctl locking

Before commit ad2f99aedf8f ("net: bridge: move bridge ioctls out of
.ndo_do_ioctl") the bridge ioctl calls were divided in two parts:
one was deviceless called by sock_ioctl and didn't expect rtnl to be held,
the other was with a device called by dev_ifsioc() and expected rtnl to be
held. After the commit above they were united in a single ioctl stub, but
it didn't take care of the locking expectations.
For sock_ioctl now we acquire  (1) br_ioctl_mutex, (2) rtnl
and for dev_ifsioc we acquire  (1) rtnl,           (2) br_ioctl_mutex

The fix is to get a refcnt on the netdev for dev_ifsioc calls and drop rtnl
then to reacquire it in the bridge ioctl stub after br_ioctl_mutex has
been acquired. That will avoid playing locking games and make the rules
straight-forward: we always take br_ioctl_mutex first, and then rtnl.

Reported-by: syzbot+34fe5894623c4ab1b379@syzkaller.appspotmail.com
Fixes: ad2f99aedf8f ("net: bridge: move bridge ioctls out of .ndo_do_ioctl")
Signed-off-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
index 86f6d7e..67c6024 100644 (file)
--- a/net/bridge/br_if.c
+++ b/net/bridge/br_if.c
@@ -456,7 +456,7 @@ int br_add_bridge(struct net *net, const char *name)
        dev_net_set(dev, net);
        dev->rtnl_link_ops = &br_link_ops;
 
-       res = register_netdev(dev);
+       res = register_netdevice(dev);
        if (res)
                free_netdev(dev);
        return res;
@@ -467,7 +467,6 @@ int br_del_bridge(struct net *net, const char *name)
        struct net_device *dev;
        int ret = 0;
 
-       rtnl_lock();
        dev = __dev_get_by_name(net, name);
        if (dev == NULL)
                ret =  -ENXIO;  /* Could not find device */
@@ -485,7 +484,6 @@ int br_del_bridge(struct net *net, const char *name)
        else
                br_dev_delete(dev, NULL);
 
-       rtnl_unlock();
        return ret;
 }
 

diff --git a/net/bridge/br_ioctl.c b/net/bridge/br_ioctl.c
index 46a24c2..2f848de 100644 (file)
--- a/net/bridge/br_ioctl.c
+++ b/net/bridge/br_ioctl.c
@@ -369,33 +369,44 @@ static int old_deviceless(struct net *net, void __user *uarg)
 int br_ioctl_stub(struct net *net, struct net_bridge *br, unsigned int cmd,
                  struct ifreq *ifr, void __user *uarg)
 {
+       int ret = -EOPNOTSUPP;
+
+       rtnl_lock();
+
        switch (cmd) {
        case SIOCGIFBR:
        case SIOCSIFBR:
-               return old_deviceless(net, uarg);
-
+               ret = old_deviceless(net, uarg);
+               break;
        case SIOCBRADDBR:
        case SIOCBRDELBR:
        {
                char buf[IFNAMSIZ];
 
-               if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
-                       return -EPERM;
+               if (!ns_capable(net->user_ns, CAP_NET_ADMIN)) {
+                       ret = -EPERM;
+                       break;
+               }
 
-               if (copy_from_user(buf, uarg, IFNAMSIZ))
-                       return -EFAULT;
+               if (copy_from_user(buf, uarg, IFNAMSIZ)) {
+                       ret = -EFAULT;
+                       break;
+               }
 
                buf[IFNAMSIZ-1] = 0;
                if (cmd == SIOCBRADDBR)
-                       return br_add_bridge(net, buf);
-
-               return br_del_bridge(net, buf);
+                       ret = br_add_bridge(net, buf);
+               else
+                       ret = br_del_bridge(net, buf);
        }
-
+               break;
        case SIOCBRADDIF:
        case SIOCBRDELIF:
-               return add_del_if(br, ifr->ifr_ifindex, cmd == SIOCBRADDIF);
-
+               ret = add_del_if(br, ifr->ifr_ifindex, cmd == SIOCBRADDIF);
+               break;
        }
-       return -EOPNOTSUPP;
+
+       rtnl_unlock();
+
+       return ret;
 }

diff --git a/net/core/dev_ioctl.c b/net/core/dev_ioctl.c
index 4035bce..ff16326 100644 (file)
--- a/net/core/dev_ioctl.c
+++ b/net/core/dev_ioctl.c
@@ -379,7 +379,12 @@ static int dev_ifsioc(struct net *net, struct ifreq *ifr, void __user *data,
        case SIOCBRDELIF:
                if (!netif_device_present(dev))
                        return -ENODEV;
-               return br_ioctl_call(net, netdev_priv(dev), cmd, ifr, NULL);
+               dev_hold(dev);
+               rtnl_unlock();
+               err = br_ioctl_call(net, netdev_priv(dev), cmd, ifr, NULL);
+               dev_put(dev);
+               rtnl_lock();
+               return err;
 
        case SIOCSHWTSTAMP:
                err = net_hwtstamp_validate(ifr);