[PATCH] watchdog: aspeed: fix integer overflow in set_timeout handler

[Tao Ren <rentao.bupt@gmail.com>]

On Thu, Apr 15, 2021 at 05:50:32PM -0700, Guenter Roeck wrote:
> On 4/15/21 5:12 PM, rentao.bupt at gmail.com wrote:
> > From: Tao Ren <rentao.bupt@gmail.com>
> > 
> > Fix the time comparison (timeout vs. max_hw_heartbeat_ms) in set_timeout
> > handler to avoid potential integer overflow when the supplied timeout is
> > greater than aspeed's maximum allowed timeout (4294 seconds).
> > 
> > Fixes: efa859f7d786 ("watchdog: Add Aspeed watchdog driver")
> > Reported-by: Amithash Prasad <amithash@fb.com>
> > Signed-off-by: Tao Ren <rentao.bupt@gmail.com>
> > ---
> >  drivers/watchdog/aspeed_wdt.c | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/watchdog/aspeed_wdt.c b/drivers/watchdog/aspeed_wdt.c
> > index 7e00960651fa..9f77272dc906 100644
> > --- a/drivers/watchdog/aspeed_wdt.c
> > +++ b/drivers/watchdog/aspeed_wdt.c
> > @@ -145,9 +145,8 @@ static int aspeed_wdt_set_timeout(struct watchdog_device *wdd,
> >  	struct aspeed_wdt *wdt = to_aspeed_wdt(wdd);
> >  	u32 actual;
> >  
> > -	wdd->timeout = timeout;
> > -
> > -	actual = min(timeout, wdd->max_hw_heartbeat_ms * 1000);
> > +	actual = min(timeout, wdd->max_hw_heartbeat_ms / 1000);
> > +	wdd->timeout = actual;
> >  
> >  	writel(actual * WDT_RATE_1MHZ, wdt->base + WDT_RELOAD_VALUE);
> >  	writel(WDT_RESTART_MAGIC, wdt->base + WDT_RESTART);
> > 
> 
> If the provided timeout is larger than the supported hardware timeout,
> the watchdog core will ping the hardware on behalf of userspace.
> The above code would defeat that mechanism for no good reason.
> 
> NACK.
> 
> Guenter

Thanks Guenter for Joel for the quick review!

The integer overflow happens at (actual * WDT_RATE_1MHZ). For example,
if a user tries to set timeout to 4295 seconds, then the hardware would
be programmed to timeout after about 32 milliseconds. I would say this
behavior is not expected?


Cheers,

Tao