[PATCH net] RDMA/core: fix UAF in ib_get_eth_speed

[Denis Kirjanov <kirjanov@gmail.com>]

call to ib_device_get_netdev from ib_get_eth_speed
may lead to a race condition while accessing a netdevice
instance since we don't hold the rtnl lock while checking
the registration state:
	if (res && res->reg_state != NETREG_REGISTERED) {

Reported-by: syzbot+5fe14f2ff4ccbace9a26@syzkaller.appspotmail.com
Fixes: d41861942fc55 ("IB/core: Add generic function to extract IB speed from netdev")
Signed-off-by: Denis Kirjanov <dkirjanov@suse.de>
---
 drivers/infiniband/core/verbs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/infiniband/core/verbs.c b/drivers/infiniband/core/verbs.c
index 94a7f3b0c71c..aa4f642e7de9 100644
--- a/drivers/infiniband/core/verbs.c
+++ b/drivers/infiniband/core/verbs.c
@@ -1976,11 +1976,11 @@ int ib_get_eth_speed(struct ib_device *dev, u32 port_num, u16 *speed, u8 *width)
 	if (rdma_port_get_link_layer(dev, port_num) != IB_LINK_LAYER_ETHERNET)
 		return -EINVAL;
 
+	rtnl_lock();
 	netdev = ib_device_get_netdev(dev, port_num);
 	if (!netdev)
 		return -ENODEV;
 
-	rtnl_lock();
 	rc = __ethtool_get_link_ksettings(netdev, &lksettings);
 	rtnl_unlock();
 
-- 
2.30.2