bnxt_en: Drop oversize TX packets to prevent errors. [Linux 5.0]

bnxt_en: Drop oversize TX packets to prevent errors. [Linux 5.0]

This Linux kernel change "bnxt_en: Drop oversize TX packets to prevent errors" is included in the Linux 5.0 release. This change is authored by Michael Chan <michael.chan [at] broadcom.com> on Wed Feb 27 03:58:53 2019 -0500. The commit for this change in Linux stable tree is 2b3c688 (patch).

bnxt_en: Drop oversize TX packets to prevent errors.

There have been reports of oversize UDP packets being sent to the
driver to be transmitted, causing error conditions.  The issue is
likely caused by the dst of the SKB switching between 'lo' with
64K MTU and the hardware device with a smaller MTU.  Patches are
being proposed by Mahesh Bandewar <[email protected]> to fix the
issue.

In the meantime, add a quick length check in the driver to prevent
the error.  The driver uses the TX packet size as index to look up an
array to setup the TX BD.  The array is large enough to support all MTU
sizes supported by the driver.  The oversize TX packet causes the
driver to index beyond the array and put garbage values into the
TX BD.  Add a simple check to prevent this.

Signed-off-by: Michael Chan <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

There are 6 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/net/ethernet/broadcom/bnxt/bnxt.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
index d95730c..803f799 100644
--- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c
+++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
@@ -500,6 +500,12 @@ static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
    }

    length >>= 9;
+   if (unlikely(length >= ARRAY_SIZE(bnxt_lhint_arr))) {
+       dev_warn_ratelimited(&pdev->dev, "Dropped oversize %d bytes TX packet.\n",
+                    skb->len);
+       i = 0;
+       goto tx_dma_error;
+   }
    flags |= bnxt_lhint_arr[length];
    txbd->tx_bd_len_flags_type = cpu_to_le32(flags);

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