Re: xfs: commit 6552321831dc "xfs: remove i_iolock and use i_rwsem in the VFS inode instead" change causes hang

[Mimi Zohar <zohar@linux.vnet.ibm.com>]

On Sun, 2017-01-08 at 19:26 +0000, Al Viro wrote:
> On Sun, Jan 08, 2017 at 08:09:55PM +0100, Christoph Hellwig wrote:
> 
> > No.  We need an ->ima_measure file_operation, guts of process_measurement
> > turned into a library function that the FS can call after taking fs-specific
> > locks.  And maybe also a small wrapper around it that takes ilock and
> > can be used directly for file systems not needing special locking.
> 
> Incidentally, it had been literally years since the problems with their
> pathname handling had been brought up and we *still* have got no answer.

> In the current tree, ima_d_path() is quite capable of returning
> path->dentry->d_name.name.  Which gets used by subsequent code,
> even though there is no warranty whatsoever that it won't be
> pointing to freed memory by the time the caller of ima_d_path()
> gets it.

The pathname/filename is being used in the measurement list and for
audit logging.  It's currently using d_absolute_path() to get the full
pathname, but falls back to using the dentry->d_name.name on failure.
Ok, so instead of returning the dentry->d_name.name, we should make a
copy it, assuming the error isn't memory related.

Mimi