On Sun, Sep 17, 2017 at 8:17 AM, Christoph Hellwig <h...@infradead.org> wrote:
>
> Only for direct I/O, and IMA and direct I/O don't work together.
> From ima_collect_measurement:
>
> if (file->f_flags & O_DIRECT) {
> audit_cause = "failed(directio)";
> result = -EACCES;
> goto out;
> }
That's not the issue.
The issue is that somebody else can come in - using direct IO - at the
same time as the first person is collecting measurements, and thus
race with the collector.
So now the measurements are not trustworthy any more.
> Well, that's exactly the point of the new ->integrity_read routine
> I proposed and prototype. The important thing is that it is called
> with i_rwsem held because code mugh higher in the chain already
> acquired it, but except for that it's entirely up to the file system.
.. and *my* point is that it's the wrong lock for actually checking
integrity (it doesn't actually guarantee exclusion, even though in
practice it's almost always the case), and so we're adding a nasty
callback that in 99% of all cases is the same as the normal read, and
we *could* have just added it with a RWF flag instead.
Is there some reason why integrity has to use that particular lock
that is so inconvenient for the filesystems it wants to check?
Linus
