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When we have a bridge with vlan_filtering on and a vlan device on top of
it, packets would be corrupted in skb_vlan_untag() called from
br_dev_xmit().
The problem sits in skb_reorder_vlan_header() used in skb_vlan_untag(),
which makes use of skb->mac_len. In this function mac_len is meant for
handling rx path with vlan devices with reorder_header disabled, but in
tx path mac_len is typically 0 and cannot be used, which is the problem
in this case.
The current code even does not properly handle rx path (skb_vlan_untag()
called from __netif_receive_skb_core()) with reorder_header off actually.
In rx path single tag case, it works as follows:
- Before skb_reorder_vlan_header()
mac_header data
v v
+-------------------+-------------+------+----
| ETH | VLAN | ETH |
| ADDRS | TPID | TCI | TYPE |
+-------------------+-------------+------+----
<-------- mac_len --------->
<------------->
to be removed
- After skb_reorder_vlan_header()
mac_header data
v v
+-------------------+------+----
| ETH | ETH |
| ADDRS | TYPE |
+-------------------+------+----
<-------- mac_len --------->
This is ok, but in rx double tag case, it corrupts packets:
- Before skb_reorder_vlan_header()
mac_header data
v v
+-------------------+-------------+-------------+------+----
| ETH | VLAN | VLAN | ETH |
| ADDRS | TPID | TCI | TPID | TCI | TYPE |
+-------------------+-------------+-------------+------+----
<--------------- mac_len ---------------->
<------------->
should be removed
<--------------------------->
actually will be removed
- After skb_reorder_vlan_header()
mac_header data
v v
+-------------------+------+----
| ETH | ETH |
| ADDRS | TYPE |
+-------------------+------+----
<--------------- mac_len ---------------->
So, two of vlan tags are both removed while only inner one should be
removed and mac_header (and mac_len) is broken.
skb_vlan_untag() is meant for removing the vlan header at (skb->data - 2),
so use skb->data and skb->mac_header to calculate the right offset.
Reported-by: Brandon Carpenter <brandon.carpenter@cypherpath.com>
Fixes: a6e18ff111 ("vlan: Fix untag operations of stacked vlans with REORDER_HEADER off")
Signed-off-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>
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