linux-kernel - Re: [PATCH] media: cec: avoid wraparound in timer interval calculation

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Message-ID: <cff4d412-abbf-44b5-9705-ba14dff7d5d0@wanadoo.fr>
Date: Sat, 1 Mar 2025 12:32:30 +0100
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Vitaliy Shevtsov <v.shevtsov@...integration.ru>,
 Hans Verkuil <hverkuil@...all.nl>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>,
 Jani Nikula <jani.nikula@...el.com>, linux-media@...r.kernel.org,
 linux-kernel@...r.kernel.org, lvc-project@...uxtesting.org
Subject: Re: [PATCH] media: cec: avoid wraparound in timer interval
 calculation

Le 01/03/2025 à 12:09, Vitaliy Shevtsov a écrit :
> [Why]
> The timer function code may have an integer wraparound issue. Since both
> pin->tx_custom_low_usecs and pin->tx_custom_high_usecs can be set to up to
> 9999999 from the user space via cec_pin_error_inj_parse_line(), this may
> cause usecs to be overflowed when adap->monitor_pin_cnt is zero and usecs
> is multiplied by 1000.
> 
> [How]
> Fix this by casting usecs to u64 when it is being converted from
> microseconds to nanoseconds.
> 
> Found by Linux Verification Center (linuxtesting.org) with Svace.
> 
> Fixes: 865463fc03ed ("media: cec-pin: add error injection support")
> Signed-off-by: Vitaliy Shevtsov <v.shevtsov@...integration.ru>
> ---
>   drivers/media/cec/core/cec-pin.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/media/cec/core/cec-pin.c b/drivers/media/cec/core/cec-pin.c
> index a70451d99ebc..f15ed5c67a65 100644
> --- a/drivers/media/cec/core/cec-pin.c
> +++ b/drivers/media/cec/core/cec-pin.c
> @@ -1021,7 +1021,7 @@ static enum hrtimer_restart cec_pin_timer(struct hrtimer *timer)
>   		pin->wait_usecs = 0;
>   		pin->timer_ts = ktime_add_us(ts, usecs);
>   		hrtimer_forward_now(timer,
> -				ns_to_ktime(usecs * 1000));
> +				ns_to_ktime((u64)usecs * 1000));

Or maybe us_to_ktime() to be less verbose?

CJ

>   		return HRTIMER_RESTART;
>   	}
>   	pin->wait_usecs = usecs - 100;