linux-kernel - Re: [PATCH] vfs/eCryptfs: Handle ioctl calls with unlocked and compat functions

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Date:	Fri, 21 May 2010 09:03:25 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Tyler Hicks <tyhicks@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Dustin Kirkland <kirkland@...onical.com>,
	Ecryptfs <ecryptfs-devel@...ts.launchpad.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Kacur <jkacur@...hat.com>,
	Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] vfs/eCryptfs: Handle ioctl calls with unlocked and
	compat functions

On Fri, May 21, 2010 at 08:25:32AM +0200, Arnd Bergmann wrote:
> On Friday 21 May 2010, Tyler Hicks wrote:
> > Lower filesystems that only implement unlocked_ioctl aren't being
> > passed ioctl calls because eCryptfs only checked for
> > lower_file->f_op->ioctl and returned -ENOTTY if it was NULL.
> > 
> > eCryptfs shouldn't implement ioctl(), since it doesn't require the BKL.
> > Instead, unlocked_ioctl() should be used and vfs_ioctl() can be called
> > on the lower file since it handles locking, if necessary.  This requires
> > vfs_ioctl() to be exported.
> 
> Calling vfs_ioctl doesn't help you at all here, you could simply call
> the ->unlocked_ioctl function of the lower fs directly to do the same,
> because ->ioctl will be gone soon.



Yeah. Nothing is left pending in the fs tree wrt ioctl pushdown so this
is safe.



> You are howevers still missing a few calls that are done through do_vfs_ioctl
> or file_ioctl.  To implement these, you need to add the file and super operations
> that these call and forward the functions to the lower fs.
> 
> > +#ifdef CONFIG_COMPAT
> > +static long
> > +ecryptfs_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> > +{
> > +	long rc = -ENOTTY;
> > +	struct file *lower_file = NULL;
> > +
> > +	if (ecryptfs_file_to_private(file))
> > +		lower_file = ecryptfs_file_to_lower(file);
> > +	if (lower_file && lower_file->f_op && lower_file->f_op->compat_ioctl)
> > +		rc = lower_file->f_op->compat_ioctl(lower_file, cmd, arg);
> > +	return rc;
> > +}
> > +#endif
> 
> You need to return -ENOIOCTLCMD here, not ENOTTY to cover the case where
> the lower file system does not have a ->compat_ioctl function but has its
> calls listed in fs/compat_ioctl.c.
> 
> 	Arnd



Right.

So I'll drop the pushdown from my tree and let Tyler handle that.

Thanks.

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