Commit c1102e9d authored by Di Zhu's avatar Di Zhu Committed by David S. Miller
Browse files

net: fix a data race when get vlan device 



We encountered a crash: in the packet receiving process, we got an
illegal VLAN device address, but the VLAN device address saved in vmcore
is correct. After checking the code, we found a possible data
competition:
CPU 0:                             CPU 1:
    (RCU read lock)                  (RTNL lock)
    vlan_do_receive()		       register_vlan_dev()
      vlan_find_dev()

        ->__vlan_group_get_device()	 ->vlan_group_prealloc_vid()

In vlan_group_prealloc_vid(), We need to make sure that memset()
in kzalloc() is executed before assigning  value to vlan devices array:
=================================
kzalloc()
    ->memset(object, 0, size)

smp_wmb()

vg->vlan_devices_arrays[pidx][vidx] = array;
==================================

Because __vlan_group_get_device() function depends on this order.
otherwise we may get a wrong address from the hardware cache on
another cpu.

So fix it by adding memory barrier instruction to ensure the order
of memory operations.

Signed-off-by: default avatarDi Zhu <zhudi21@huawei.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 7ad18ff6

net/8021q/vlan.c

+3 −0
Original line number Diff line number Diff line
@@ -71,6 +71,9 @@ static int vlan_group_prealloc_vid(struct vlan_group *vg, 
	if (array == NULL)

		return -ENOBUFS;



	/* paired with smp_rmb() in __vlan_group_get_device() */

	smp_wmb();



	vg->vlan_devices_arrays[pidx][vidx] = array;

	return 0;

}

net/8021q/vlan.h

+4 −0
Original line number Diff line number Diff line
@@ -57,6 +57,10 @@ static inline struct net_device *__vlan_group_get_device(struct vlan_group *vg, 


	array = vg->vlan_devices_arrays[pidx]

				       [vlan_id / VLAN_GROUP_ARRAY_PART_LEN];



	/* paired with smp_wmb() in vlan_group_prealloc_vid() */

	smp_rmb();



	return array ? array[vlan_id % VLAN_GROUP_ARRAY_PART_LEN] : NULL;

}