linux-kernel - Re:Re: drivers/s390/char/keyboard.c NULL pointer reference

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Date:   Sat, 5 Aug 2017 09:44:45 +0800 (CST)
From:   sohu0106 <sohu0106@....com>
To:     "Heiko Carstens" <heiko.carstens@...ibm.com>
Cc:     schwidefsky@...ibm.com, linux-s390@...r.kernel.org,
        torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re:Re: drivers/s390/char/keyboard.c NULL pointer reference



I don't understand a bit,My idea is 

in userland

fd=open("tty3270",O_RDONLY)
...
ret=ioctl(fd,KDGKBDIACR,NULL)
...

then here 
drivers/s390/char/keyboard.c
477 
case KDGKBDIACR:
	{
		struct kbdiacrs __user *a = argp;
		struct kbdiacr diacr;
		int i;
		
		//a is NULL,a->kb_cnt will crash
		if (put_user(kbd->accent_table_size, &a->kb_cnt))




At 2017-08-04 17:26:08, "Heiko Carstens" <heiko.carstens@...ibm.com> wrote:
>On Thu, Aug 03, 2017 at 09:57:38PM +0800, sohu0106 wrote:
>> 
>> 
>> Local users able to send the NULL arg argument to kbd_ioctl(), which could cause kernel crash
>> 
>> 
>> 
>> 
>> diff --git a/keyboard.c 
>> b/keyboard.c
>> index ba0e4f9..3ec16b1 100644
>> --- a/keyboard.c
>> +++ b/keyboard.c
>> @@ -456,6 +456,8 @@ int kbd_ioctl(struct kbd_data *kbd, unsigned int cmd, unsigned long arg)
>>         int perm;
>>  
>>         argp = (void __user *)arg;
>> +       if( !argp )
>> +               return -EFAULT;
>
>This doesn't make sense as well. All uaccess functions are able to handle
>NULL pointers within user space.
>