Re: [PATCH] Input: MT - use __GFP_NOWARN allocation at input_mt_init_slots()

From: Dmitry Torokhov <dmitry.torokhov@gmail.com>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Henrik Rydberg <rydberg@bitmath.org>,
	syzkaller-bugs@googlegroups.com,
	syzbot <syzbot+0122fa359a69694395d5@syzkaller.appspotmail.com>,
	akpm@linux-foundation.org,
	"linux-input@vger.kernel.org" <linux-input@vger.kernel.org>
Subject: Re: [PATCH] Input: MT - use __GFP_NOWARN allocation at input_mt_init_slots()
Date: Tue, 22 Nov 2022 15:23:07 -0800	[thread overview]
Message-ID: <Y31Z29bSaH38WuAt@google.com> (raw)
In-Reply-To: <6d878e01-6c2f-8766-2578-c95030442369@I-love.SAKURA.ne.jp>

Hi Tetsuo,

On Sat, Nov 19, 2022 at 04:09:56PM +0900, Tetsuo Handa wrote:
> syzbot is reporting too large allocation at input_mt_init_slots() {1], for
> num_slots is supplied from userspace using ioctl(UI_DEV_CREATE).
> Also, replace n2 with array_size(), for 32bits variable n2 will overflow
> if num_slots >= 65536.

Not really keen on fiddling with the memory allocator flags just to
appease syzbot. Maybe keep them as is, and simply limit the number of
slots to something more reasonable, like 64, and return -EINVAL if it is
above?

> 
> Link: https://syzkaller.appspot.com/bug?extid=0122fa359a69694395d5 [1]
> Reported-by: syzbot <syzbot+0122fa359a69694395d5@syzkaller.appspotmail.com>
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> ---
>  drivers/input/input-mt.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/input/input-mt.c b/drivers/input/input-mt.c
> index 14b53dac1253..cf74579462ba 100644
> --- a/drivers/input/input-mt.c
> +++ b/drivers/input/input-mt.c
> @@ -47,7 +47,7 @@ int input_mt_init_slots(struct input_dev *dev, unsigned int num_slots,
>  	if (mt)
>  		return mt->num_slots != num_slots ? -EINVAL : 0;
>  
> -	mt = kzalloc(struct_size(mt, slots, num_slots), GFP_KERNEL);
> +	mt = kzalloc(struct_size(mt, slots, num_slots), GFP_KERNEL | __GFP_NOWARN);
>  	if (!mt)
>  		goto err_mem;
>  
> @@ -80,8 +80,8 @@ int input_mt_init_slots(struct input_dev *dev, unsigned int num_slots,
>  	if (flags & INPUT_MT_SEMI_MT)
>  		__set_bit(INPUT_PROP_SEMI_MT, dev->propbit);
>  	if (flags & INPUT_MT_TRACK) {
> -		unsigned int n2 = num_slots * num_slots;
> -		mt->red = kcalloc(n2, sizeof(*mt->red), GFP_KERNEL);
> +		mt->red = kcalloc(array_size(num_slots, num_slots),
> +				  sizeof(*mt->red), GFP_KERNEL | __GFP_NOWARN);
>  		if (!mt->red)
>  			goto err_mem;
>  	}
> -- 
> 2.34.1
> 
> 

Thanks.

-- 
Dmitry