[PATCH iwl-net v3 6/6] ixgbe: fix integer overflow and wrong bit position in ixgbe_validate_rtr()

[Aleksandr Loktionov <aleksandr.loktionov@intel.com>]

Two bugs in the same loop in ixgbe_validate_rtr():

1. The 3-bit traffic-class field was extracted by shifting a u32 and
   assigning the result directly to a u8.  For user priority 0 this is
   harmless; for UP[5..7] the shift leaves bits [15..21] in the u32
   which are then silently truncated when stored in u8.  Mask with
   IXGBE_RTRUP2TC_UP_MASK before the assignment so only the intended
   3 bits are kept.

2. When clearing an out-of-bounds entry the mask was always shifted by
   the fixed constant IXGBE_RTRUP2TC_UP_SHIFT (== 3), regardless of
   which loop iteration was being processed.  This means only UP1 (bit
   position 3) was ever cleared; UP0,2..7 (positions 0, 6, 9, ..., 21)
   were left unreset, so invalid TC mappings persisted in hardware and
   could mis-steer received packets to the wrong traffic class.
   Use i * IXGBE_RTRUP2TC_UP_SHIFT to target the correct 3-bit field
   for each iteration.

Swap the operand order in the mask expression to place the constant
on the right per kernel coding style (noted by David Laight).

Fixes: 8b1c0b24d9af ("ixgbe: configure minimal packet buffers to support TC")
Cc: stable@vger.kernel.org
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
---
v2 -> v3:
 - Correct Fixes: tag to 8b1c0b24d9af ("ixgbe: configure minimal packet
   buffers to support TC") -- the previously used e7589eab9291 predates
   the buggy code path (Simon Horman); add Reviewed-by: Simon Horman.

v1 -> v2:
 - Add Fixes: tag; reroute to iwl-net (wrong bit positions cause packet
   mis-steering); swap to (reg >> ...) & MASK operand order per David
   Laight.

 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index 210c7b9..c9e4f12 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -9772,11 +9772,12 @@ static void ixgbe_validate_rtr(struct ixgbe_adapter *adapter, u8 tc)
 	rsave = reg;
 
 	for (i = 0; i < MAX_TRAFFIC_CLASS; i++) {
-		u8 up2tc = reg >> (i * IXGBE_RTRUP2TC_UP_SHIFT);
+		u8 up2tc = (reg >> (i * IXGBE_RTRUP2TC_UP_SHIFT)) &
+			   IXGBE_RTRUP2TC_UP_MASK;
 
 		/* If up2tc is out of bounds default to zero */
 		if (up2tc > tc)
-			reg &= ~(0x7 << IXGBE_RTRUP2TC_UP_SHIFT);
+			reg &= ~(IXGBE_RTRUP2TC_UP_MASK << (i * IXGBE_RTRUP2TC_UP_SHIFT));
 	}
 
 	if (reg != rsave)
-- 
2.52.0