[PATCH][V2] net: dsa: mv88e6xxx: avoid unintended sign extension on a 16 bit shift

[Colin King]

From: Colin Ian King <colin.king@xxxxxxxxxxxxx>

The shifting of timehi by 16 bits to the left will be promoted to
a 32 bit signed int and then sign-extended to an u64. If the top bit
of timehi is set then all then all the upper bits of ns end up as also
being set because of the sign-extension. Fix this by making timehi and
timelo u64.  Also move the declaration of ns.

Detected by CoverityScan, CID#1465288 ("Unintended sign extension")

Fixes: c6fe0ad2c349 ("net: dsa: mv88e6xxx: add rx/tx timestamping support")
Signed-off-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
---
 drivers/net/dsa/mv88e6xxx/hwtstamp.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/dsa/mv88e6xxx/hwtstamp.c b/drivers/net/dsa/mv88e6xxx/hwtstamp.c
index b251d534b70d..2149d332dea0 100644
--- a/drivers/net/dsa/mv88e6xxx/hwtstamp.c
+++ b/drivers/net/dsa/mv88e6xxx/hwtstamp.c
@@ -293,7 +293,8 @@ static void mv88e6xxx_get_rxts(struct mv88e6xxx_chip *chip,
 			       struct sk_buff *skb, u16 reg,
 			       struct sk_buff_head *rxq)
 {
-	u16 buf[4] = { 0 }, status, timelo, timehi, seq_id;
+	u16 buf[4] = { 0 }, status, seq_id;
+	u64 ns, timelo, timehi;
 	struct skb_shared_hwtstamps *shwt;
 	int err;
 
@@ -321,7 +322,7 @@ static void mv88e6xxx_get_rxts(struct mv88e6xxx_chip *chip,
 	 */
 	for ( ; skb; skb = skb_dequeue(rxq)) {
 		if (mv88e6xxx_ts_valid(status) && seq_match(skb, seq_id)) {
-			u64 ns = timehi << 16 | timelo;
+			ns = timehi << 16 | timelo;
 
 			mutex_lock(&chip->reg_lock);
 			ns = timecounter_cyc2time(&chip->tstamp_tc, ns);
-- 
2.15.1