e1000e: fix flow control denial of service possibility

this patch avoids a denial of service from an evildoer sending a
continuous stream of flow control at our adapter that is plugged
into a non-flow control enabled switch.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

diff --git a/drivers/net/e1000e/lib.c b/drivers/net/e1000e/lib.c
index 0860b5f..341d74e 100644 (file)
--- a/drivers/net/e1000e/lib.c
+++ b/drivers/net/e1000e/lib.c
@@ -1104,34 +1104,13 @@ s32 e1000e_config_fc_after_link_up(struct e1000_hw *hw)
                         (mii_nway_lp_ability_reg & NWAY_LPAR_ASM_DIR)) {
                        mac->fc = e1000_fc_rx_pause;
                        hw_dbg(hw, "Flow Control = RX PAUSE frames only.\r\n");
-               }
-               /* Per the IEEE spec, at this point flow control should be
-                * disabled.  However, we want to consider that we could
-                * be connected to a legacy switch that doesn't advertise
-                * desired flow control, but can be forced on the link
-                * partner.  So if we advertised no flow control, that is
-                * what we will resolve to.  If we advertised some kind of
-                * receive capability (Rx Pause Only or Full Flow Control)
-                * and the link partner advertised none, we will configure
-                * ourselves to enable Rx Flow Control only.  We can do
-                * this safely for two reasons:  If the link partner really
-                * didn't want flow control enabled, and we enable Rx, no
-                * harm done since we won't be receiving any PAUSE frames
-                * anyway.  If the intent on the link partner was to have
-                * flow control enabled, then by us enabling RX only, we
-                * can at least receive pause frames and process them.
-                * This is a good idea because in most cases, since we are
-                * predominantly a server NIC, more times than not we will
-                * be asked to delay transmission of packets than asking
-                * our link partner to pause transmission of frames.
-                */
-               else if ((mac->original_fc == e1000_fc_none) ||
-                        (mac->original_fc == e1000_fc_tx_pause)) {
+               } else {
+                       /*
+                        * Per the IEEE spec, at this point flow control
+                        * should be disabled.
+                        */
                        mac->fc = e1000_fc_none;
                        hw_dbg(hw, "Flow Control = NONE.\r\n");
-               } else {
-                       mac->fc = e1000_fc_rx_pause;
-                       hw_dbg(hw, "Flow Control = RX PAUSE frames only.\r\n");
                }
 
                /* Now we need to do one last check...  If we auto-