[PATCH net 1/2] net: fix mac_len of skbs copied by generic XDP

[Tianyi Gao <tianyi@cloudflare.com>]

skb_pp_cow_data() copies the header fields of the old skb with
skb_copy_header(). skb_copy_header() does not copy mac_len.

Generic XDP uses skb_pp_cow_data() for programs with frags support.
After such a program, the skb can have mac_len 0.
cpu_map_generic_redirect() and tc ingress then get the position of the
Ethernet header wrong.

Copy mac_len in skb_pp_cow_data(), as dev_map_generic_redirect() does
after skb_copy().

Fixes: e6d5dbdd20aa ("xdp: add multi-buff support for xdp running in generic mode")
Signed-off-by: Tianyi Gao <tianyi@cloudflare.com>
---
 net/core/skbuff.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 48f676411724..aa0b11204708 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -967,6 +967,7 @@ int skb_pp_cow_data(struct page_pool *pool, struct sk_buff **pskb,
 
 	skb_reserve(nskb, headroom);
 	skb_copy_header(nskb, skb);
+	nskb->mac_len = skb->mac_len;
 	skb_mark_for_recycle(nskb);
 
 	err = skb_copy_bits(skb, 0, nskb->data, size);
-- 
2.55.0