linux-kernel - Re: [PATCH] ds2760: fix integer overflow for time_to_empty

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Message-ID: <20090730141259.GV19257@buzzloop.caiaq.de>
Date:	Thu, 30 Jul 2009 16:12:59 +0200
From:	Daniel Mack <daniel@...aq.de>
To:	Anton Vorontsov <avorontsov@...mvista.com>
Cc:	linux-kernel@...r.kernel.org,
	Szabolcs Gyurko <szabolcs.gyurko@....hu>,
	Matt Reimer <mreimer@...p.net>, Anton Vorontsov <cbou@...l.ru>
Subject: Re: [PATCH] ds2760: fix integer overflow for time_to_empty_now

On Thu, Jul 30, 2009 at 06:00:41PM +0400, Anton Vorontsov wrote:
> On Fri, Jul 24, 2009 at 03:19:33PM +0200, Daniel Mack wrote:
> > On the device we're currently developing, battery sizes of ~2.8Ah and
> > current flow of ~600mA are typical.
> > 
> > With that values, the life_sec computation overflows due to the
> > multiplication by 3600.
> > 
> > Signed-off-by: Daniel Mack <daniel@...aq.de>
> > Cc: Szabolcs Gyurko <szabolcs.gyurko@....hu>
> > Cc: Matt Reimer <mreimer@...p.net>
> > Cc: Anton Vorontsov <cbou@...l.ru>
> > 
> > Signed-off-by: Daniel Mack <daniel@...aq.de>
> > ---
> >  drivers/power/ds2760_battery.c |    4 ++--
> >  1 files changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/power/ds2760_battery.c b/drivers/power/ds2760_battery.c
> > index d545fee..5d30dc0 100644
> > --- a/drivers/power/ds2760_battery.c
> > +++ b/drivers/power/ds2760_battery.c
> > @@ -212,8 +212,8 @@ static int ds2760_battery_read_status(struct ds2760_device_info *di)
> >  		di->rem_capacity = 100;
> >  
> >  	if (di->current_uA)
> > -		di->life_sec = -((di->accum_current_uAh - di->empty_uAh) *
> > -				 3600L) / di->current_uA;
> > +		di->life_sec = -((di->accum_current_uAh - di->empty_uAh) * 36L)
> > +					/ (di->current_uA / 100L);
> 
> Hm... "(di->current_uA / 100L)" might result to 0, so you'll get
> div by zero. Removing the parenthesis will help.

Hmm, no, then it gets the precedence wrong. But checking for values >=
100 of current_uA helps. Thanks for spotting this.

Daniel


>From c60e23e2ba6667bec882338bfe3cb12304ee1ab6 Mon Sep 17 00:00:00 2001
From: Daniel Mack <daniel@...aq.de>
Date: Fri, 24 Jul 2009 15:08:11 +0200
Subject: [PATCH] ds2760: fix integer overflow for time_to_empty_now

On the device we're currently developing, battery sizes of ~2.8Ah and
current flow of ~600mA are typical.

With that values, the life_sec computation overflows due to the
multiplication by 3600.

Signed-off-by: Daniel Mack <daniel@...aq.de>
Cc: Szabolcs Gyurko <szabolcs.gyurko@....hu>
Cc: Matt Reimer <mreimer@...p.net>
Cc: Anton Vorontsov <cbou@...l.ru>

Signed-off-by: Daniel Mack <daniel@...aq.de>
---
 drivers/power/ds2760_battery.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/power/ds2760_battery.c b/drivers/power/ds2760_battery.c
index d545fee..2ef29dd 100644
--- a/drivers/power/ds2760_battery.c
+++ b/drivers/power/ds2760_battery.c
@@ -211,9 +211,9 @@ static int ds2760_battery_read_status(struct ds2760_device_info *di)
 	if (di->rem_capacity > 100)
 		di->rem_capacity = 100;
 
-	if (di->current_uA)
-		di->life_sec = -((di->accum_current_uAh - di->empty_uAh) *
-				 3600L) / di->current_uA;
+	if (di->current_uA >= 100L)
+		di->life_sec = -((di->accum_current_uAh - di->empty_uAh) * 36L)
+					/ (di->current_uA / 100L);
 	else
 		di->life_sec = 0;
 
-- 
1.6.3.3

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