3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Hangbin Liu <liuhang...@gmail.com>

[ Upstream commit e8238fc2bd7b4c3c7554fa2df067e796610212fc ]

When we set a bond slave's master to bridge via ioctl, we only check
the IFF_BRIDGE_PORT flag. Although we will find the slave's real master
at netdev_master_upper_dev_link() later, it already does some settings
and allocates some resources. It would be better to return as early
as possible.

v1 -> v2:
use netdev_master_upper_dev_get() instead of netdev_has_any_upper_dev()
to check if we have a master, because not all upper devs are masters,
e.g. vlan device.

Reported-by: syzbot+de73361ee4971b6e6...@syzkaller.appspotmail.com
Signed-off-by: Hangbin Liu <liuhang...@gmail.com>
Acked-by: Nikolay Aleksandrov <niko...@cumulusnetworks.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 net/bridge/br_if.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/net/bridge/br_if.c
+++ b/net/bridge/br_if.c
@@ -445,8 +445,8 @@ int br_add_if(struct net_bridge *br, str
        if (dev->netdev_ops->ndo_start_xmit == br_dev_xmit)
                return -ELOOP;
 
-       /* Device is already being bridged */
-       if (br_port_exists(dev))
+       /* Device has master upper dev */
+       if (netdev_master_upper_dev_get(dev))
                return -EBUSY;
 
        /* No bridging devices that dislike that (e.g. wireless) */


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