net: fix bpf_xdp_adjust_head regression for generic-XDP

When generic-XDP was moved to a later processing step by commit
458bf2f224f0 ("net: core: support XDP generic on stacked devices.")
a regression was introduced when using bpf_xdp_adjust_head.

The issue is that after this commit the skb->network_header is now
changed prior to calling generic XDP and not after. Thus, if the header
is changed by XDP (via bpf_xdp_adjust_head), then skb->network_header
also need to be updated again.  Fix by calling skb_reset_network_header().

Fixes: 458bf2f224f0 ("net: core: support XDP generic on stacked devices.")
Reported-by: Brandon Cazander <brandon.cazander@multapplied.net>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev.c b/net/core/dev.c
index 2f341b8508456ecc110302fb1959703735540b96..0891f499c1bb7cdb85490a681b21895f2206bcba 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4374,12 +4374,17 @@ static u32 netif_receive_generic_xdp(struct sk_buff *skb,
 
        act = bpf_prog_run_xdp(xdp_prog, xdp);
 
+       /* check if bpf_xdp_adjust_head was used */
        off = xdp->data - orig_data;
-       if (off > 0)
-               __skb_pull(skb, off);
-       else if (off < 0)
-               __skb_push(skb, -off);
-       skb->mac_header += off;
+       if (off) {
+               if (off > 0)
+                       __skb_pull(skb, off);
+               else if (off < 0)
+                       __skb_push(skb, -off);
+
+               skb->mac_header += off;
+               skb_reset_network_header(skb);
+       }
 
        /* check if bpf_xdp_adjust_tail was used. it can only "shrink"
         * pckt.