Date:	Wed, 10 Mar 2010 18:19:32 -0600
From:	H Hartley Sweeten <hartleys@...ionengravers.com>
To:	Simon Horman <horms@...ge.net.au>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>,
	"greg@...ah.com" <greg@...ah.com>, "ss@....gov.au" <ss@....gov.au>
Subject: RE: [PATCH] staging/dt3155: make copy_{to/from}_user and put_user
 typesafe

On Wednesday, March 10, 2010 5:01 PM, Simon Horman wrote:
> On Thu, Mar 04, 2010 at 10:20:18AM -0700, H Hartley Sweeten wrote:
>> This makes the kernel to user space data transfers typesafe and removes
>> a number of unnecessary (void *) casts.
>
> Could you be more specific about what you mean by typesafe?
> There still seem to be casts in there. Although fewer than before :-)

>From include/asm-generic/uaccess.h

static inline long copy_from_user(void *to,
		const void __user * from, unsigned long n)
{
	might_sleep();
	if (access_ok(VERIFY_READ, from, n))
		return __copy_from_user(to, from, n);
	else
		return n;
}

static inline long copy_to_user(void __user *to,
		const void *from, unsigned long n)
{
	might_sleep();
	if (access_ok(VERIFY_WRITE, to, n))
		return __copy_to_user(to, from, n);
	else
		return n;
}

>> Signed-off-by: H Hartley Sweeten <hsweeten@...ionengravers.com>
>> Cc: Greg Kroah-Hartman <greg@...ah.com>
>> Cc: Scott Smedley <ss@....gov.au>
>> 
>> ---
>> 
>> diff --git a/drivers/staging/dt3155/dt3155_drv.c b/drivers/staging/dt3155/dt3155_drv.c
>> index a67c622..76c9d94 100644
>> --- a/drivers/staging/dt3155/dt3155_drv.c
>> +++ b/drivers/staging/dt3155/dt3155_drv.c
>> @@ -528,6 +528,7 @@ static int dt3155_ioctl(struct inode *inode,
>>  			unsigned long arg)
>>  {
>>    int minor = MINOR(inode->i_rdev); /* What device are we ioctl()'ing? */
>> +  void __user *up = (void __user *)arg;

This cast is needed, and common, since 'arg' is passed as an unsigned long.
The cast to __user memory space does not produce a sparse error.

>>  
>>    if ( minor >= MAXBOARDS || minor < 0 )
>>      return -ENODEV;
>> @@ -554,7 +555,7 @@ static int dt3155_ioctl(struct inode *inode,
>>  
>>  	{
>>  	  struct dt3155_config_s tmp;
>> -	  if (copy_from_user((void *)&tmp, (void *) arg, sizeof(tmp)))

The fist void * cast is unnecessary, the second produces a sparse warning
since copy_from_user expects 'arg' to be a __user space pointer.

>> +	  if (copy_from_user(&tmp, up, sizeof(tmp)))

Using the 'up' (user pointer) variable quiets the warning and makes the
function call typesafe (ok maybe that's the wrong term...).

>>  	      return -EFAULT;
>>  	  /* check for valid settings */
>>  	  if (tmp.rows > DT3155_MAX_ROWS ||
>> @@ -572,8 +573,7 @@ static int dt3155_ioctl(struct inode *inode,
>>        }
>>      case DT3155_GET_CONFIG:
>>        {
>> -	if (copy_to_user((void *) arg, (void *) &dt3155_status[minor],
>> -		     sizeof(dt3155_status_t) ))

Here 'arg' should be a __user space pointer and the second cast is not
necessary.

>> +	if (copy_to_user(up, &dt3155_status[minor], sizeof(dt3155_status_t)))

Again, using 'up' fixes the sparse warning.

The two below are the same.

>>  	    return -EFAULT;
>>  	return 0;
>>        }
>> @@ -593,8 +593,7 @@ static int dt3155_ioctl(struct inode *inode,
>>  	  return 0;
>>  
>>  	quick_stop(minor);
>> -	if (copy_to_user((void *) arg, (void *) &dt3155_status[minor],
>> -		     sizeof(dt3155_status_t)))
>> +	if (copy_to_user(up, &dt3155_status[minor], sizeof(dt3155_status_t)))
>>  	    return -EFAULT;
>>  	return 0;
>>        }
>> @@ -617,8 +616,7 @@ static int dt3155_ioctl(struct inode *inode,
>>  	  }
>>  
>>  	dt3155_init_isr(minor);
>> -	if (copy_to_user( (void *) arg, (void *) &dt3155_status[minor],
>> -		      sizeof(dt3155_status_t)))
>> +	if (copy_to_user(up, &dt3155_status[minor], sizeof(dt3155_status_t)))
>>  	    return -EFAULT;
>>  	return 0;
>>        }
>> @@ -819,11 +817,11 @@ static ssize_t dt3155_read(struct file *filep, char __user *buf,
>>    /* make this an offset */
>>    offset = frame_info_p->addr - dt3155_status[minor].mem_addr;
>>  
>> -  put_user(offset, (unsigned int *) buf);
>> +  put_user(offset, (unsigned int __user *)buf);

For put_user, the second argument should be a __user pointer. 'buf' comes into the
function correctly (char __user *) but needs the cast here so that the correct
'size' of data is copied to __user space.  Same below.

>>    buf += sizeof(u32);
>> -  put_user( dt3155_status[minor].fbuffer.frame_count, (unsigned int *) buf);
>> +  put_user( dt3155_status[minor].fbuffer.frame_count, (unsigned int __user *)buf);
>>    buf += sizeof(u32);
>> -  put_user(dt3155_status[minor].state, (unsigned int *) buf);
>> +  put_user(dt3155_status[minor].state, (unsigned int __user *)buf);
>>    buf += sizeof(u32);
>>    if (copy_to_user(buf, frame_info_p, sizeof(frame_info_t)))
>>        return -EFAULT;

All of this seems pretty common in other kernel code.  And it removes a number of
the sparse warnings generated by this file.

Regards,
Hartley
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