Re: [BUG] vrf: attaching a packet tap to a VRF device corrupts skb->csum for packets from L3 ingress devices (Udp6InCsumErrors, packets dropped)

[Ido Schimmel <idosch@idosch.org>]

On Sat, Sep 05, 2026 at 02:59:13PM +0200, Stefano Sasso wrote:
> Naively, the fix looks like it should be to make the accounting symmetric:
> either drop the `skb_postpush_rcsum()` call, since the push/pull pair leaves the
> packet unchanged, or add the matching `skb_postpull_rcsum()` before
> `skb_pull_inline()`. I do not feel qualified to say which is correct, or whether
> there are other callers/paths that rely on the current behaviour, so I am not
> sending a patch.

I believe your analysis is correct. I will test [1]. Drivers that
support CHECKSUM_COMPLETE don't include the checksum of the Ethernet
header in skb->csum.

[1]
diff --git a/drivers/net/vrf.c b/drivers/net/vrf.c
index a0557a3a7026..d4dc6d690a75 100644
--- a/drivers/net/vrf.c
+++ b/drivers/net/vrf.c
@@ -1175,8 +1175,6 @@ static int vrf_prepare_mac_header(struct sk_buff *skb,
 	skb->protocol = eth->h_proto;
 	skb->pkt_type = PACKET_HOST;
 
-	skb_postpush_rcsum(skb, skb->data, ETH_HLEN);
-
 	skb_pull_inline(skb, ETH_HLEN);
 
 	return 0;