linux-kernel - Re: xfs: commit 6552321831dc "xfs: remove i_iolock and use i_rwsem in the VFS inode instead" change causes hang

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Message-Id: <1483887789.8189.90.camel@linux.vnet.ibm.com>
Date:   Sun, 08 Jan 2017 10:03:09 -0500
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     Christoph Hellwig <hch@....de>
Cc:     linux-xfs@...r.kernel.org, Dave Chinner <david@...morbit.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...IV.linux.org.uk>
Subject: Re: xfs:  commit 6552321831dc "xfs: remove i_iolock and use    i_rwsem
 in the VFS inode instead"  change causes hang

On Sun, 2017-01-08 at 15:52 +0100, Christoph Hellwig wrote:
> On Sun, Jan 08, 2017 at 09:48:44AM -0500, Mimi Zohar wrote:
> > IMA takes the i_rwsem (fomerly i_mutex) before reading the file to
> > synchronize calculating the file hash and validating the file's
> > hash/signature stored as security.ima xattr
> 
> Well, it shouldn't do that.  In the I/O path i_rwsem is up to the
> fs to use.  Various other file systems also take it internally for
> reads, although mostly only for direct I/O.

But not normally for a normal file read.  For direct I/O, IMA fails the
file hash/signature verification, measurement, audit unless the IMA
"permit_directio" rule is defined.

> So the answer here is that ima needs to stop playing with i_rwsem.

Unless something has changed recently, to synchronize reading files to
calculate the file hash and writing xattrs it has to take the i_rwsem
prior to reading the file.

Mimi