[PATCH] net/sched: cbs: perform rate conversions in signed 64-bit arithmetic

[Jack Wang <163wangjack@gmail.com>]

cbs_set_port_rate() and cbs_change() multiply link rates and slope values
by BYTES_PER_KBIT, an unsigned long constant.  On 32-bit architectures,
the multiplications therefore take place in 32-bit unsigned arithmetic
before the results are assigned to s64 fields.

For port rates above approximately 34.36 Gbit/s this wraps port_rate.
The same conversion turns a negative sendslope into a large positive
value, reversing the CBS credit adjustment.  This affects software CBS;
port_rate is also refreshed on NETDEV_UP and NETDEV_CHANGE notifications.

Cast the first operand of each multiplication to s64 so all intermediate
operations use signed 64-bit arithmetic and preserve the value's sign on
every architecture.

Fixes: 585d763af09c ("net/sched: Introduce Credit Based Shaper (CBS) qdisc")
Fixes: 397006ba5d918 ("net/sched: cbs: Fix integer overflow in cbs_set_port_rate()")

Signed-off-by: Jack Wang <163wangjack@gmail.com>
---
 net/sched/sch_cbs.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/sched/sch_cbs.c b/net/sched/sch_cbs.c
index 1c93469c56e3..9ef31ecdaa05 100644
--- a/net/sched/sch_cbs.c
+++ b/net/sched/sch_cbs.c
@@ -335,7 +335,7 @@ static void cbs_set_port_rate(struct net_device *dev, struct cbs_sched_data *q)
 		speed = ecmd.base.speed;
 
 skip:
-	port_rate = speed * 1000 * BYTES_PER_KBIT;
+	port_rate = (s64)speed * 1000 * BYTES_PER_KBIT;
 
 	atomic64_set(&q->port_rate, port_rate);
 	netdev_dbg(dev, "cbs: set %s's port_rate to: %lld, linkspeed: %d\n",
@@ -405,8 +405,8 @@ static int cbs_change(struct Qdisc *sch, struct nlattr *opt,
 	/* Everything went OK, save the parameters used. */
 	WRITE_ONCE(q->hicredit, qopt->hicredit);
 	WRITE_ONCE(q->locredit, qopt->locredit);
-	WRITE_ONCE(q->idleslope, qopt->idleslope * BYTES_PER_KBIT);
-	WRITE_ONCE(q->sendslope, qopt->sendslope * BYTES_PER_KBIT);
+	WRITE_ONCE(q->idleslope, (s64)qopt->idleslope * BYTES_PER_KBIT);
+	WRITE_ONCE(q->sendslope, (s64)qopt->sendslope * BYTES_PER_KBIT);
 	WRITE_ONCE(q->offload, qopt->offload);
 
 	return 0;
-- 
2.53.0