Re: IMA + O_DIRECT (Re: [PATCH 0/1] fix IMA + Apparmor kernel panic)

[Mimi Zohar]

On Fri, 2014-05-09 at 18:56 +0100, Al Viro wrote: 
> On Fri, May 09, 2014 at 12:10:03PM +0900, J. R. Okajima wrote:
> > 
> > Dmitry Kasatkin:
> > > Following patch replaces IMA usage of kernel_read() with special
> > > version which skips security check that triggers kernel panic
> > > when Apparmor and IMA appraisal are enabled together.
> > 
> > I know this is related to exit(2), but this behaviour of IMA is related
> > to open(2) too.
> > When O_DIRECT is specified, some filesystems (for example, ext2) call
> > do_blockdev_direct_IO() which acquires i_mutex. But
> > IMA:process_measurement() already acquires i_mutex before kernel_read().
> > It causes a deadlock even if you replace kernel_read() by a simpler one.
> > How can we stop reading the file from IMA?
> 
> Disabling it would be a good start...  And no, I'm not kidding - the mess
> you are proposing is such that it's not at all obvious that this stuff
> is worth the trouble.

Al, perhaps we didn't do a good job describing the different use case
scenarios for the different aspects of the integrity subsystem.  Are you
interested in hearing about them?

> Why the devil is it playing with ->i_mutex?  IMA, that is.  Its use for
> data is absolutely fs-dependent.  Again, filesystem is *NOT* required
> to take ->i_mutex anywhere on the write path.  At all.

Agreed it shouldn't be taking the i_mutex.  However, there was a lock
ordering issue when writing extended attributes, which does take the
i_mutex.

Mimi

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