RE: [PATCH V3 2/2] Move stack parameters for sed_ioctl to prevent oversized stack with CONFIG_KASAN

[David Laight]

From: Johannes Thumshirn
> Sent: 10 February 2017 07:46
> On 02/09/2017 06:20 PM, Scott Bauer wrote:
> > When CONFIG_KASAN is enabled, compilation fails:

Does CONFIG_KASAN allocate guard stack space around everything that
is passed by address?
That sounds completely brain-dead.
There are a lot of functions that have an 'int *' argument to return
a single value - and are never going to do anything else.

...
> > Moved all the ioctl structures off the stack and dynamically activate
> > using _IOC_SIZE()
...
> 
> > -		if (copy_from_user(&session, arg, sizeof(session)))
> > -			return -EFAULT;
> > -		return opal_erase_locking_range(dev, &session);
> > +	ioctl_ptr = kzalloc(cmd_size, GFP_KERNEL);
> > +	if (!ioctl_ptr)
> > +		return -ENOMEM;
> > +	if (copy_from_user(ioctl_ptr, arg, cmd_size)) {
> > +		ret = -EFAULT;
> > +		goto out;
> >  	}
> 
> Can't we use memdup_user() instead of kzalloc() + copy_from_user()?

You either want the copy_from_user() or the memzero() not both.

ISTM there could be two 'library' functions, maybe:
void *get_ioctl_buf(unsigned int cmd, long arg)
to malloc the buffer, memzero/copy_from_user, returns -EFAULT if copy fails.
int put_ioctl_buf(int rval, unsigned int cmd, const void *buf)
does copy_to_user() if rval >= 0 and IOR_READ, then frees buf.
return value is rval unless the copyout fails.

	David