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Subject[PATCH 4.14 258/496] net: Fix vlan untag for bridge and vlan_dev with reorder_hdr off
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

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

From: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>

[ Upstream commit 4bbb3e0e8239f9079bf1fe20b3c0cb598714ae61 ]

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: a6e18ff11170 ("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>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/uapi/linux/if_ether.h | 1 +
net/core/skbuff.c | 7 +++++--
2 files changed, 6 insertions(+), 2 deletions(-)

--- a/include/uapi/linux/if_ether.h
+++ b/include/uapi/linux/if_ether.h
@@ -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 */
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4939,13 +4939,16 @@ EXPORT_SYMBOL_GPL(skb_gso_validate_mtu);

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;
}

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