From: Shmulik Ladkani <shmulik.ladk...@gmail.com>
In case 'skb_vlan_push' is called on an skb with a hw-accel vlan tag
present, the existing hw-accel tag is inserted into the payload, and
the new given tag is placed as new hw-accel tag.
In order to insert the existing hw-accel tag, 'skb_vlan_push' adjusts
the 'data' pointer at the mac_header (if needed), invokes __vlan_insert_tag,
and finally re-adjusts 'data' back to its original position (according
to the remembered "adjustment offset").
However, successful '__vlan_insert_tag' pushes 4 more bytes at start of
frame.
Alas, the remembered "adjustment offset" is NOT fixed to account for
these additional 4 bytes, so the subsequent '__skb_pull(skb, offset)'
fails to unwind 'data' back to its original location.
Since 'skb->mac_len' IS fixed to account for the additional 4 bytes
(incremented to a total of 18 bytes), any access to
'skb->data - skb->mac_len' points to bytes PRIOR start of frame.
This is problematic, as many constructs in the stack are issuing
'skb_push(skb, skb->mac_len)' prior xmit to a device (e.g tcf_mirred,
tcf_bpf, nf_dup_netdev_egress), resulting in bogus frames being
xmitted (having random 4 bytes at start of frame).
For example:
# ip l add dev d0 type dummy
# tc filter add dev eth0 parent ffff: pref 1 basic \
action vlan push protocol 802.1ad id 5 pipe \
action mirred egress redirect dev d0
Any 802.1q (hw-accel) tagged frames arriving on eth0 are xmitted as
bogus frames on d0; whereas the expected behavior is having QinQ frames.
Fix, by properly accouting the additionally pushed 4 bytes (in the case
where an adjustment to point at mac_header was done).
Fixes: 93515d53b1 ("net: move vlan pop/push functions into common code")
Signed-off-by: Shmulik Ladkani <shmulik.ladk...@gmail.com>
Cc: Pravin Shelar <pshe...@ovn.org>
Cc: Jiri Pirko <j...@mellanox.com>
---
v2: Instead of reducing mac_len by 4 bytes, which was found incorrect,
fix the problem of wrong unwinding of 'skb->data'
David, if patch ok, suggest this goes to -stable
net/core/skbuff.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index d36c754..3926b79 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4608,6 +4608,8 @@ int skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto,
u16 vlan_tci)
skb->protocol = skb->vlan_proto;
skb->mac_len += VLAN_HLEN;
+ if (offset)
+ offset += VLAN_HLEN;
skb_postpush_rcsum(skb, skb->data + (2 * ETH_ALEN), VLAN_HLEN);
__skb_pull(skb, offset);
--
1.9.1
