On Tue, Jan 21, 2025 at 4:15 PM Stephan Wurm [off-list ref] wrote:

I did some additional experiments.

First, I was able to get v6.13 running on the system, although it did
not fix my issue.

Then I played around with VLAN interfaces.

I created an explicit VLAN interface on top of the prp interface. In that
case the VLAN header gets transparently attached to the tx frames and
forwarding through the interface layers works as expected.

It was even possible to get my application working on top of the vlan
interface, but it resulted in two VLAN headers - the inner from the
application, the outer from the vlan interface.

So when sending vlan tagged frames directly from an application through
a prp interface the mac_len field does not get updated, even though the
VLAN protocol header is properly detected; when sending frames through
an explicit vlan interface, the mac_len seems to be properly parsed
into the skb.

Now I am running out of ideas how to proceed.

For the time being I would locally revert this fix, to make my
application working again.
But I can support in testing proposed solutions.

If mac_len can not be used, we need yet another pskb_may_pull()

I am unsure why hsr_get_node() is working, since it also uses skb->mac_len

Please test the following patch :

diff --git a/net/hsr/hsr_forward.c b/net/hsr/hsr_forward.c
index 87bb3a91598ee96b825f7aaff53aafb32ffe4f9..8942592130c151f2c948308e1ae16a6736822d5

100644

--- a/net/hsr/hsr_forward.c
+++ b/net/hsr/hsr_forward.c

@@ -700,9 +700,11 @@ static int fill_frame_info(struct hsr_frame_info *frame,
                frame->is_vlan = true;

        if (frame->is_vlan) {
-               if (skb->mac_len < offsetofend(struct hsr_vlan_ethhdr, vlanhdr))
+               if (pskb_may_pull(skb,
+                                 skb_mac_offset(skb) +
+                                 offsetofend(struct hsr_vlan_ethhdr, vlanhdr)))
                        return -EINVAL;
-               vlan_hdr = (struct hsr_vlan_ethhdr *)ethhdr;
+               vlan_hdr = (struct hsr_vlan_ethhdr *)skb_mac_header(skb);
                proto = vlan_hdr->vlanhdr.h_vlan_encapsulated_proto;
        }