linux-kernel - Re: [PATCH] drm/repaper: fix integer overflows in repeat functions

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Message-ID: <cac5924e-5653-4385-b18f-6c7f1f8d6e8b@tronnes.org>
Date: Thu, 13 Feb 2025 18:08:32 +0100
From: Noralf Trønnes <noralf@...nnes.org>
To: Nikita Zhandarovich <n.zhandarovich@...tech.ru>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 Alex Lanzano <lanzano.alex@...il.com>
Cc: David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 lvc-project@...uxtesting.org
Subject: Re: [PATCH] drm/repaper: fix integer overflows in repeat functions

Adding Alex who is now the driver maintainer.


On 13.02.2025 17:57, Nikita Zhandarovich wrote:
> Gentle ping :)
> 
> On 1/16/25 16:48, Nikita Zhandarovich wrote:
>> There are conditions, albeit somewhat unlikely, under which right hand
>> expressions, calculating the end of time period in functions like
>> repaper_frame_fixed_repeat(), may overflow.
>>
>> For instance, if 'factor10x' in repaper_get_temperature() is high
>> enough (170), as is 'epd->stage_time' in repaper_probe(), then the
>> resulting value of 'end' will not fit in unsigned int expression.
>>
>> Mitigate this by casting 'epd->factored_stage_time' to wider type before
>> any multiplication is done.
>>
>> Found by Linux Verification Center (linuxtesting.org) with static
>> analysis tool SVACE.
>>
>> Fixes: 3589211e9b03 ("drm/tinydrm: Add RePaper e-ink driver")
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Nikita Zhandarovich <n.zhandarovich@...tech.ru>
>> ---
>>  drivers/gpu/drm/tiny/repaper.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/tiny/repaper.c b/drivers/gpu/drm/tiny/repaper.c
>> index 77944eb17b3c..d76c0e8e05f5 100644
>> --- a/drivers/gpu/drm/tiny/repaper.c
>> +++ b/drivers/gpu/drm/tiny/repaper.c
>> @@ -456,7 +456,7 @@ static void repaper_frame_fixed_repeat(struct repaper_epd *epd, u8 fixed_value,
>>  				       enum repaper_stage stage)
>>  {
>>  	u64 start = local_clock();
>> -	u64 end = start + (epd->factored_stage_time * 1000 * 1000);
>> +	u64 end = start + ((u64)epd->factored_stage_time * 1000 * 1000);
>>  
>>  	do {
>>  		repaper_frame_fixed(epd, fixed_value, stage);
>> @@ -467,7 +467,7 @@ static void repaper_frame_data_repeat(struct repaper_epd *epd, const u8 *image,
>>  				      const u8 *mask, enum repaper_stage stage)
>>  {
>>  	u64 start = local_clock();
>> -	u64 end = start + (epd->factored_stage_time * 1000 * 1000);
>> +	u64 end = start + ((u64)epd->factored_stage_time * 1000 * 1000);
>>  
>>  	do {
>>  		repaper_frame_data(epd, image, mask, stage);
>