linux-kernel - RE: [PATCH V3 2/2] Move stack parameters for sed_ioctl to prevent oversized stack with CONFIG

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Date:   Fri, 10 Feb 2017 10:28:17 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Johannes Thumshirn' <jthumshirn@...e.de>,
        Scott Bauer <scott.bauer@...el.com>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>
CC:     "arnd@...db.de" <arnd@...db.de>, "axboe@...com" <axboe@...com>,
        "keith.busch@...el.com" <keith.busch@...el.com>,
        "jonathan.derrick@...el.com" <jonathan.derrick@...el.com>,
        "hch@...radead.org" <hch@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>
Subject: RE: [PATCH V3 2/2] Move stack parameters for sed_ioctl to prevent
 oversized stack with CONFIG_KASAN

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