Re: [PATCH v3 10/12] ima: defer calling __fput()

[Mimi Zohar]

On Thu, 2012-03-22 at 14:22 +0000, Al Viro wrote:
> On Wed, Mar 21, 2012 at 02:54:15PM -0400, Mimi Zohar wrote:
> > If a file is closed before it is munmapped, __fput() is called with
> > the mmap_sem taken.  With IMA-appraisal enabled, this results in an
> > mmap_sem/i_mutex lockdep.  ima_defer_fput() increments the f_count
> > to defer __fput() being called until after the mmap_sem is released.
> 
> NAK.  It's far too heavy-weight for what's a very common path.  Worse,
> it causes different locking conditions on IMA and non-IMA kernels and makes
> bugs harder to spot.  Rejected with extreme prejudice; please, fix your
> locking instead.

Al, thanks for replying!  I realize you are very prejudiced against IMA,
but have you taken a look at IMA-appraisal?  It probably would have been
better if we used another name in order to avoid this prejudice, but
unfortunately we didn't.  :(  IMA-appraisal is about enforcing file
integrity.

> BTW, you've missed several other places in mm/* doing fput(), so it wouldn't
> be enough to paper over your problem anyway.
> 
> Final fput() *can* happen under mmap_sem.  Period.

I think I got that loud and clear; otherwise we wouldn't have come up
with deferring the __fput().  We have a very real problem here - writing
extended attributes requires taking the i_mutex.  I'm open to any
suggestions.

thanks,

Mimi

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/