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Date:   Sun, 17 Sep 2017 08:17:57 -0700
From:   Christoph Hellwig <>
To:     Linus Torvalds <>
Cc:     Mimi Zohar <>,
        LSM List <>,
        Christoph Hellwig <>,,
        Christoph Hellwig <>,
        James Morris <>,
        Linux Kernel Mailing List <>,
        Matthew Garrett <>,
        Jan Kara <>, Theodore Ts'o <>,
        Andreas Dilger <>,
        Jaegeuk Kim <>, Chao Yu <>,
        Steven Whitehouse <>,
        Bob Peterson <>,
        David Woodhouse <>,
        Dave Kleikamp <>,
        Ryusuke Konishi <>,
        Mark Fasheh <>,
        Joel Becker <>,
        Richard Weinberger <>,
        "Darrick J. Wong" <>,
        Hugh Dickins <>, Chris Mason <>
Subject: Re: [PATCH 3/3] ima: use fs method to read integrity data (updated
 patch description)

On Sat, Sep 16, 2017 at 11:20:47AM -0700, Linus Torvalds wrote:
> Sure, generic_file_write_iter() does take that lock exclusively, but
> not everybody uses generic_file_write_iter() at all for writing.
> For example, xfs still uses that i_rwsem, but for block-aligned writes
> it will only get it shared. And I'm not convinced some other
> filesystem might not end up using some other lock entirely.

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;

(and yes, it should be checking for IOCB_DIRECT to avoid racy
f_flags manipulations, but that's another issue)

> The filesystem can do its own locking, and I'm starting to think that
> it would be better to just pass this "this is an integrity read" down
> to the filesystem, and expect the filesystem to do the locking based
> on that.

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.

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