[PATCH v3 net 3/7] net: enetc: fix bogus TX ring consumer index after reinitialization

The TBCIR (Transmit Buffer Descriptor Ring Consumer Index) register has
the BD index as the lower 16 bits, but the upper 16 bits contain this
field:

  STAT_ID: Status identifier. Incremented each time the BDR_INDEX is
  updated and an error status bit was set for one of the processed BDs.
  Clears on read.

If there was any transmit error prior to the ring reinitialization and
this is the first time we re-read the TBCIR register, reading it will
give us a value with non-zero upper bits, which is saved in
bdr->next_to_clean.

If subsequently NAPI gets invoked and enetc_clean_tx_ring() runs, this
will dereference the &tx_ring->tx_swbd[] for the bogus (and huge)
next_to_clean index, and will result in an out-of-bounds memory access.

Other places like enetc_bd_ready_count() do mask out the upper bits, so
let's do that here as well.

Fixes: d4fd0404c1c9 ("enetc: Introduce basic PF and VF ENETC ethernet drivers")
Reviewed-by: Wei Fang <wei.fang@nxp.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
v1->v3: none
---
 drivers/net/ethernet/freescale/enetc/enetc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
index c9c23e994f6d..0216f7d08e19 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc.c

@@ -2627,7 +2627,8 @@ static void enetc_setup_txbdr(struct enetc_hw *hw, struct enetc_bdr *tx_ring)
 	 * adjust sw indexes
 	 */
 	tx_ring->next_to_use = enetc_txbdr_rd(hw, idx, ENETC_TBPIR);
-	tx_ring->next_to_clean = enetc_txbdr_rd(hw, idx, ENETC_TBCIR);
+	tx_ring->next_to_clean = enetc_txbdr_rd(hw, idx, ENETC_TBCIR) &
+				 ENETC_TBCIR_IDX_MASK;
 
 	if (tx_ring->next_to_use != tx_ring->next_to_clean &&
 	    !is_enetc_rev1(si)) {

-- 
2.43.0