8139cp: Fix GSO MSS handling

When fixing the TSO support I noticed we just mask ->gso_size with the
MSSMask value and don't care about the consequences.

Provide a .ndo_features_check() method which drops the NETIF_F_TSO
feature for any skb which would exceed the maximum, and thus forces it
to be segmented by software.

Then we can stop the masking in cp_start_xmit(), and just WARN if the
maximum is exceeded, which should now never happen.

Finally, Francois Romieu noticed that we didn't even have the right
value for MSSMask anyway; it should be 0x7ff (11 bits) not 0xfff.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 18 insertions, 2 deletions

diff --git a/drivers/net/ethernet/realtek/8139cp.c b/drivers/net/ethernet/realtek/8139cp.c
index e5173f33428b..deae10d7426d 100644
--- a/drivers/net/ethernet/realtek/8139cp.c
+++ b/drivers/net/ethernet/realtek/8139cp.c
@@ -175,7 +175,7 @@ enum {
         LastFrag        = (1 << 28), /* Final segment of a packet */
         LargeSend       = (1 << 27), /* TCP Large Send Offload (TSO) */
         MSSShift        = 16,        /* MSS value position */
-        MSSMask         = 0xfff,     /* MSS value: 11 bits */
+        MSSMask         = 0x7ff,     /* MSS value: 11 bits */
         TxError         = (1 << 23), /* Tx error summary */
         RxError         = (1 << 20), /* Rx error summary */
         IPCS            = (1 << 18), /* Calculate IP checksum */
@@ -754,10 +754,16 @@ static netdev_tx_t cp_start_xmit (struct sk_buff *skb,
         eor = (entry == (CP_TX_RING_SIZE - 1)) ? RingEnd : 0;
         mss = skb_shinfo(skb)->gso_size;
 
+        if (mss > MSSMask) {
+                WARN_ONCE(1, "Net bug: GSO size %d too large for 8139CP\n",
+                          mss);
+                goto out_dma_error;
+        }
+
         opts2 = cpu_to_le32(cp_tx_vlan_tag(skb));
         opts1 = DescOwn;
         if (mss)
-                opts1 |= LargeSend | ((mss & MSSMask) << MSSShift);
+                opts1 |= LargeSend | (mss << MSSShift);
         else if (skb->ip_summed == CHECKSUM_PARTIAL) {
                 const struct iphdr *ip = ip_hdr(skb);
                 if (ip->protocol == IPPROTO_TCP)
@@ -1852,6 +1858,15 @@ static void cp_set_d3_state (struct cp_private *cp)
         pci_set_power_state (cp->pdev, PCI_D3hot);
 }
 
+static netdev_features_t cp_features_check(struct sk_buff *skb,
+                                           struct net_device *dev,
+                                           netdev_features_t features)
+{
+        if (skb_shinfo(skb)->gso_size > MSSMask)
+                features &= ~NETIF_F_TSO;
+
+        return vlan_features_check(skb, features);
+}
 static const struct net_device_ops cp_netdev_ops = {
         .ndo_open               = cp_open,
         .ndo_stop               = cp_close,
@@ -1864,6 +1879,7 @@ static const struct net_device_ops cp_netdev_ops = {
         .ndo_tx_timeout         = cp_tx_timeout,
         .ndo_set_features       = cp_set_features,
         .ndo_change_mtu         = cp_change_mtu,
+        .ndo_features_check     = cp_features_check,
 
 #ifdef CONFIG_NET_POLL_CONTROLLER
         .ndo_poll_controller    = cp_poll_controller,