[PATCH v1 iwl-net] ice: fix potential NULL pointer deref in error path of ice_set_ringparam()

[Kohei Enju <kohei@enjuk.jp>]

ice_set_ringparam nullifies tstamp_ring of temporary tx_rings, without
clearing ICE_TX_RING_FLAGS_TXTIME bit.
When ICE_TX_RING_FLAGS_TXTIME is set and the subsequent
ice_setup_tx_ring() call fails, a NULL pointer dereference could happen
in the unwinding sequence:

ice_clean_tx_ring()
-> ice_is_txtime_cfg() == true (ICE_TX_RING_FLAGS_TXTIME is set)
-> ice_free_tx_tstamp_ring()
  -> ice_free_tstamp_ring()
    -> tstamp_ring->desc (NULL deref)

Clear ICE_TX_RING_FLAGS_TXTIME bit to avoid the potential issue.

Note that this potential issue is found by manual code review.
Compile test only since unfortunately I don't have E830 devices.

Fixes: ccde82e90946 ("ice: add E830 Earliest TxTime First Offload support")
Signed-off-by: Kohei Enju <kohei@enjuk.jp>
---
 drivers/net/ethernet/intel/ice/ice_ethtool.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/ethernet/intel/ice/ice_ethtool.c b/drivers/net/ethernet/intel/ice/ice_ethtool.c
index 7f769a90dde1..5ed86648d0d6 100644
--- a/drivers/net/ethernet/intel/ice/ice_ethtool.c
+++ b/drivers/net/ethernet/intel/ice/ice_ethtool.c
@@ -3290,6 +3290,7 @@ ice_set_ringparam(struct net_device *netdev, struct ethtool_ringparam *ring,
 		tx_rings[i].desc = NULL;
 		tx_rings[i].tx_buf = NULL;
 		tx_rings[i].tstamp_ring = NULL;
+		clear_bit(ICE_TX_RING_FLAGS_TXTIME, tx_rings[i].flags);
 		tx_rings[i].tx_tstamps = &pf->ptp.port.tx;
 		err = ice_setup_tx_ring(&tx_rings[i]);
 		if (err) {
-- 
2.51.0