Messages in this thread | | | From | Vladimir Oltean <> | Date | Tue, 3 Sep 2019 13:12:41 +0300 | Subject | Re: [PATCH] net: sched: taprio: Fix potential integer overflow in taprio_set_picos_per_byte |
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On Tue, 3 Sep 2019 at 10:19, Eric Dumazet <eric.dumazet@gmail.com> wrote: > > > > On 9/3/19 3:08 AM, Gustavo A. R. Silva wrote: > > Add suffix LL to constant 1000 in order to avoid a potential integer > > overflow and give the compiler complete information about the proper > > arithmetic to use. Notice that this constant is being used in a context > > that expects an expression of type s64, but it's currently evaluated > > using 32-bit arithmetic. > > > > Addresses-Coverity-ID: 1453459 ("Unintentional integer overflow") > > Fixes: f04b514c0ce2 ("taprio: Set default link speed to 10 Mbps in taprio_set_picos_per_byte") > > Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com> > > --- > > net/sched/sch_taprio.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c > > index 8d8bc2ec5cd6..956f837436ea 100644 > > --- a/net/sched/sch_taprio.c > > +++ b/net/sched/sch_taprio.c > > @@ -966,7 +966,7 @@ static void taprio_set_picos_per_byte(struct net_device *dev, > > > > skip: > > picos_per_byte = div64_s64(NSEC_PER_SEC * 1000LL * 8, > > - speed * 1000 * 1000); > > + speed * 1000LL * 1000); > > > > atomic64_set(&q->picos_per_byte, picos_per_byte); > > netdev_dbg(dev, "taprio: set %s's picos_per_byte to: %lld, linkspeed: %d\n", > > > > But, why even multiplying by 1,000,000 in the first place, this seems silly, > a standard 32 bit divide could be used instead. > > -> > > diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c > index 8d8bc2ec5cd6281d811fd5d8a5c5211ebb0edd73..944b1af3215668e927d486b6c6c65c4599fb9539 100644 > --- a/net/sched/sch_taprio.c > +++ b/net/sched/sch_taprio.c > @@ -965,8 +965,7 @@ static void taprio_set_picos_per_byte(struct net_device *dev, > speed = ecmd.base.speed; > > skip: > - picos_per_byte = div64_s64(NSEC_PER_SEC * 1000LL * 8, > - speed * 1000 * 1000); > + picos_per_byte = (USEC_PER_SEC * 8) / speed; > > atomic64_set(&q->picos_per_byte, picos_per_byte); > netdev_dbg(dev, "taprio: set %s's picos_per_byte to: %lld, linkspeed: %d\n", > > >
Right. And while we're at it, there's still the potential division-by-zero problem which I still don't know how to solve without implementing a full-blown __ethtool_get_link_ksettings parser that checks against all the possible outputs it can have under the "no carrier" condition - see "[RFC PATCH 1/1] phylink: Set speed to SPEED_UNKNOWN when there is no PHY connected" for details. And there's also a third fix to be made: the netdev_dbg should be made to print "speed" instead of "ecmd.base.speed".
Thanks, -Vladimir
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