[net] bpf, xdp, i40e: fix i40e_build_skb skb reserve and truesize

[Jeff Kirsher]

From: Daniel Borkmann <dan...@iogearbox.net>

Using skb_reserve(skb, I40E_SKB_PAD + (xdp->data - xdp->data_hard_start))
is clearly wrong since I40E_SKB_PAD already points to the offset where
the original xdp->data was sitting since xdp->data_hard_start is defined
as xdp->data - i40e_rx_offset(rx_ring) where latter offsets to I40E_SKB_PAD
when build skb is used.

However, also before cc5b114dcf98 ("bpf, i40e: add meta data support")
this seems broken since bpf_xdp_adjust_head() helper could have been used
to alter headroom and enlarge / shrink the frame and with that the assumption
that the xdp->data remains unchanged does not hold and would push a bogus
packet to upper stack.

ixgbe got this right in 924708081629 ("ixgbe: add XDP support for pass and
drop actions"). In any case, fix it by removing the I40E_SKB_PAD from both
skb_reserve() and truesize calculation.

Fixes: cc5b114dcf98 ("bpf, i40e: add meta data support")
Fixes: 0c8493d90b6b ("i40e: add XDP support for pass and drop actions")
Reported-by: Keith Busch <keith.bu...@linux.intel.com>
Reported-by: Toshiaki Makita <makita.toshi...@lab.ntt.co.jp>
Signed-off-by: Daniel Borkmann <dan...@iogearbox.net>
Cc: Björn Töpel <bjorn.to...@intel.com>
Cc: John Fastabend <john.fastab...@gmail.com>
Tested-by: Keith Busch <keith.bu...@linux.intel.com>
Acked-by: John Fastabend <john.fastab...@gmail.com>
Acked-by: Alexander Duyck <alexander.h.du...@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirs...@intel.com>
---
 drivers/net/ethernet/intel/i40e/i40e_txrx.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c 
b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
index 8ffb7454e67c..ed6dbcfd4e96 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
@@ -2103,9 +2103,8 @@ static struct sk_buff *i40e_build_skb(struct i40e_ring 
*rx_ring,
        unsigned int truesize = i40e_rx_pg_size(rx_ring) / 2;
 #else
        unsigned int truesize = SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) +
-                               SKB_DATA_ALIGN(I40E_SKB_PAD +
-                                              (xdp->data_end -
-                                               xdp->data_hard_start));
+                               SKB_DATA_ALIGN(xdp->data_end -
+                                              xdp->data_hard_start);
 #endif
        struct sk_buff *skb;
 
@@ -2124,7 +2123,7 @@ static struct sk_buff *i40e_build_skb(struct i40e_ring 
*rx_ring,
                return NULL;
 
        /* update pointers within the skb to store the data */
-       skb_reserve(skb, I40E_SKB_PAD + (xdp->data - xdp->data_hard_start));
+       skb_reserve(skb, xdp->data - xdp->data_hard_start);
        __skb_put(skb, xdp->data_end - xdp->data);
        if (metasize)
                skb_metadata_set(skb, metasize);
-- 
2.17.1