Re: [PATCH v3 1/1] ovl: setxattr: don't deadlock when called from ima_fix_xattr.

[Mimi Zohar]

On Mon, 2016-05-30 at 16:10 +0200, Miklos Szeredi wrote:
> On Fri, May 20, 2016 at 11:53:18PM +0300, Krisztian Litkey wrote:
> > On Fri, May 20, 2016 at 8:00 PM, Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> wrote:
> 
> > > We deferred __fput() back in 2012 in order for IMA to safely take the
> > > i_mutex and write security.ima.   Writing the security.ima xattr now
> > > triggers overlayfs to write the xattr, but overlayfs doesn't
> > > differentiate between callers - as a result of userspace or as described
> > > here in __fput().   All calls to ovl_setxattr() should call vfs_sexattr,
> > > except the one triggered by __fput().   Refer to the original lockdep
> > > report -
> > > http://thread.gmane.org/gmane.linux.file-systems.union/640
> 
> Looks like more fallout from 4bacc9c9234c ("overlayfs: Make f_path always point
> to the overlay and f_inode to the underlay").
> 
> Not sure what we want here.  Doing everything on the underlying dentry/inode
> would be trivial (see attached patch).
> 
> Question is, can we get setxattr() on file opened for O_RDONLY?  If so, then
> that could fail on overlayfs (lower layer is read-only).

Normally only after a file has been modified is the xattr written.
However in "fix" mode, the xattr would be written for files opened
read-only (eg. bprm, mmap execute).

Mimi