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

Jack Wang [off-list ref] writes:

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 <redacted>
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Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>


Cheers,
-- 
Vinicius