From: Mimi Zohar <zohar@linux.vnet.ibm.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>, Greg KH <greg@kroah.com>,
Andrew Morton <akpm@linux-foundation.org>,
Dmitry Kasatkin <dmitry.kasatkin@intel.com>,
linux-fsdevel@vger.kernel.org,
linux-security-module@vger.kernel.org, viro@zeniv.linux.org.uk,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 1/1] vfs: iversion truncate bug fix
Date: Thu, 05 Jan 2012 17:27:29 -0500 [thread overview]
Message-ID: <1325802450.2062.54.camel@falcor.watson.ibm.com> (raw)
In-Reply-To: 20120105181401.GA418@infradead.org
On Thu, 2012-01-05 at 14:49 -0500, Mimi Zohar wrote:
> On Thu, 2012-01-05 at 13:14 -0500, Christoph Hellwig wrote:
> > On Thu, Jan 05, 2012 at 03:53:54PM +1100, Dave Chinner wrote:
> > > That's seems like a rather unreliable way of detecting that a file
> > > has changed to me. I mean, only ext4 uses inode_inc_version() when
> > > it internally dirties an inode, and only ext4 sets the MS_I_VERSION
> > > so that inode_inc_version is only called for ext4 inodes when
> > > timestamps change.
> >
> > And even ext4 only does it when using the non-default "i_version"
> > mount option.
> >
> > > Hence just adding an increment to the truncate case doesn't seem to
> > > be sufficient to me. e.g. what about the equivalent case of having a
> > > hole punched in the file via fallocate? The file has definitely
> > > changed, but i_version won't change....
> > >
> > > Perhaps bumping i_version in __mark_inode_dirty() might be the best
> > > way to capture all changes (other than timestamp updates) to any
> > > inode regardless of the filesystem type?
> >
> > It has the same problem as the timestamp updates doing that right now -
> > the fs can't do locking around it, and it can't return errors. That's
> > something affecting at least btrfs, xfs and IIRC ubifs, and probably
> > the cluster filesystems as well. The right answer is to replace the
> > timestmap updates which are the only places doing that with a method
> > as Josef had planned to do, and then we can include the i_version
> > updates in there.
> >
> > That assumes we figure out a coherent way to do it - except for the
> > conditional abuse in file_updates_times it's currently entirely under
> > fs control. So the best way to fix it would be to:
> >
> > - move the fs-private use into those filesystems actually using it.
> > Note that a lot less actually check for it rather than just updating
> > it based on some cargo cult, and most only do so for directories.
> > - figure a why what exact change count semantics NFS (and IMA) want
> > and find a way to implement them so that the fs can tell the callers
> > that they don't exist.
> >
> > Btw, does IMA care about these beeing persistent?
>
> By 'persistent' I assume you mean across boots. IMA (and IMA-appraisal)
> measure and appraise files the first time they're accessed/executed. So
> no, it does not need to be persistent. IMA/IMA-appraisal just need some
> way to detect file change in order to know whether the file needs to be
> re-measured/appraised on subsequent access.
One other IMA requirement would be the ability to detect if a file
mmapped executable, after the point that it has been locked from
modification, has changed since the last time measured/appraised. The
concern here, in particular, is the ability to detect file change while
holding the mmap_sem.
thanks,
Mimi
next prev parent reply other threads:[~2012-01-05 22:30 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-22 10:54 [PATCH v3 1/1] vfs: iversion truncate bug fix Dmitry Kasatkin
2011-12-22 13:26 ` Mimi Zohar
2012-01-04 23:28 ` Andrew Morton
2012-01-05 0:33 ` Mimi Zohar
2012-01-05 0:46 ` Andrew Morton
2012-01-05 2:06 ` Greg KH
2012-01-05 4:17 ` Mimi Zohar
2012-01-05 4:53 ` Dave Chinner
2012-01-05 18:14 ` Christoph Hellwig
2012-01-05 19:49 ` Mimi Zohar
2012-01-05 21:36 ` J. Bruce Fields
2012-01-05 22:27 ` Mimi Zohar [this message]
2012-01-05 16:54 ` Greg KH
2012-01-05 17:19 ` Mimi Zohar
2012-01-05 18:39 ` James Bottomley
2012-01-05 22:30 ` Andrew Morton
2012-01-05 23:09 ` Mimi Zohar
2012-01-13 10:13 ` Kasatkin, Dmitry
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