[PATCH 4.14 002/110] ixgbe: fix crash in build_skb Rx code path

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Emil Tantilov <emil.s.tantilov@xxxxxxxxx>

commit 0c5661ecc5dd7ce296870a3eb7b62b1b280a5e89 upstream.

Add check for build_skb enabled ring in ixgbe_dma_sync_frag().
In that case &skb_shinfo(skb)->frags[0] may not always be set which
can lead to a crash. Instead we derive the page offset from skb->data.

Fixes: 42073d91a214 ("ixgbe: Have the CPU take ownership of the buffers sooner")
CC: stable <stable@xxxxxxxxxxxxxxx>
Reported-by: Ambarish Soman <asoman@xxxxxxxxxx>
Suggested-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxx>
Signed-off-by: Emil Tantilov <emil.s.tantilov@xxxxxxxxx>
Tested-by: Andrew Bowers <andrewx.bowers@xxxxxxxxx>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -1877,6 +1877,14 @@ static void ixgbe_dma_sync_frag(struct i
 				     ixgbe_rx_pg_size(rx_ring),
 				     DMA_FROM_DEVICE,
 				     IXGBE_RX_DMA_ATTR);
+	} else if (ring_uses_build_skb(rx_ring)) {
+		unsigned long offset = (unsigned long)(skb->data) & ~PAGE_MASK;
+
+		dma_sync_single_range_for_cpu(rx_ring->dev,
+					      IXGBE_CB(skb)->dma,
+					      offset,
+					      skb_headlen(skb),
+					      DMA_FROM_DEVICE);
 	} else {
 		struct skb_frag_struct *frag = &skb_shinfo(skb)->frags[0];