linux-kernel - Re: [PATCH] Input: uinput - fix undefined behavior in uinput_validate

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Date:   Mon, 14 Jan 2019 14:07:56 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     linux-input@...r.kernel.org
Cc:     Byoungyoung Lee <lifeasageek@...il.com>, rydberg@...math.org,
        DaeRyong Jeong <threeearcat@...il.com>,
        syzkaller@...glegroups.com,
        Peter Hutterer <peter.hutterer@...-t.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Input: uinput - fix undefined behavior in
 uinput_validate_absinfo()

On Mon, Jan 14, 2019 at 02:04:48PM -0800, Dmitry Torokhov wrote:
> An integer overflow may arise in uinput_validate_absinfo() if "max - min"
> can't be represented by an "int". We should check for overflow before
> trying to use the result.
> 
> Reported-by: Kyungtae Kim <kt0755@...il.com>
> Cc: stable@...r.kernel.org
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> ---
>  drivers/input/misc/uinput.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c
> index 8ec483e8688b..26ec603fe220 100644
> --- a/drivers/input/misc/uinput.c
> +++ b/drivers/input/misc/uinput.c
> @@ -39,6 +39,7 @@
>  #include <linux/init.h>
>  #include <linux/fs.h>
>  #include <linux/miscdevice.h>
> +#include <linux/overflow.h>
>  #include <linux/input/mt.h>
>  #include "../input-compat.h"
>  
> @@ -405,7 +406,7 @@ static int uinput_open(struct inode *inode, struct file *file)
>  static int uinput_validate_absinfo(struct input_dev *dev, unsigned int code,
>  				   const struct input_absinfo *abs)
>  {
> -	int min, max;
> +	int min, max, range;
>  
>  	min = abs->minimum;
>  	max = abs->maximum;
> @@ -417,7 +418,7 @@ static int uinput_validate_absinfo(struct input_dev *dev, unsigned int code,
>  		return -EINVAL;
>  	}
>  
> -	if (abs->flat > max - min) {
> +	if (check_sub_overflow(max, min, &range) && abs->flat > range) {

This should be !check_sub_overflow(...) of course.

>  		printk(KERN_DEBUG
>  		       "%s: abs_flat #%02x out of range: %d (min:%d/max:%d)\n",
>  		       UINPUT_NAME, code, abs->flat, min, max);
> -- 
> 2.20.1.97.g81188d93c3-goog
> 
> 
> -- 
> Dmitry

-- 
Dmitry