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net: Fix vlan untag for bridge and vlan_dev with reorder_hdr off

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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>
This commit is contained in:
Toshiaki Makita 2018-03-13 14:51:27 +09:00 committed by David S. Miller
parent 51d4740f88
commit 4bbb3e0e82
2 changed files with 6 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/uapi/linux/if_ether.h
View File

@ -30,6 +30,7 @@
*/
#define ETH_ALEN 6 /* Octets in one ethernet addr */
#define ETH_TLEN 2 /* Octets in ethernet type field */
#define ETH_HLEN 14 /* Total octets in header. */
#define ETH_ZLEN 60 /* Min. octets in frame sans FCS */
#define ETH_DATA_LEN 1500 /* Max. octets in payload */

7
net/core/skbuff.c
View File

@ -5020,13 +5020,16 @@ EXPORT_SYMBOL_GPL(skb_gso_validate_mac_len);
static struct sk_buff *skb_reorder_vlan_header(struct sk_buff *skb)
{
int mac_len;
if (skb_cow(skb, skb_headroom(skb)) < 0) {
kfree_skb(skb);
return NULL;
}
memmove(skb->data - ETH_HLEN, skb->data - skb->mac_len - VLAN_HLEN,
2 * ETH_ALEN);
mac_len = skb->data - skb_mac_header(skb);
memmove(skb_mac_header(skb) + VLAN_HLEN, skb_mac_header(skb),
mac_len - VLAN_HLEN - ETH_TLEN);
skb->mac_header += VLAN_HLEN;
return skb;
}