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Sender: Guenter Roeck <groeck7@gmail.com>
Subject: Re: [PATCH] watchdog: aspeed: fix integer overflow in set_timeout
 handler
To:     rentao.bupt@gmail.com, Wim Van Sebroeck <wim@linux-watchdog.org>,
        Joel Stanley <joel@jms.id.au>,
        Andrew Jeffery <andrew@aj.id.au>,
        linux-watchdog@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-aspeed@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        openbmc@lists.ozlabs.org, Tao Ren <taoren@fb.com>,
        Amithash Prasad <amithash@fb.com>
References: <20210416001208.16788-1-rentao.bupt@gmail.com>
From:   Guenter Roeck <linux@roeck-us.net>
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Message-ID: <469ac948-d65b-471f-102f-726466c19c5c@roeck-us.net>
Date:   Thu, 15 Apr 2021 17:50:32 -0700
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On 4/15/21 5:12 PM, rentao.bupt@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