Received-SPF: pass (google.com: best guess record for domain of linux-ext4-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   David Laight <David.Laight@ACULAB.COM>
To:     "'ira.weiny@intel.com'" <ira.weiny@intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     Alexander Viro <viro@zeniv.linux.org.uk>,
        "Darrick J. Wong" <darrick.wong@oracle.com>,
        Dan Williams <dan.j.williams@intel.com>,
        "Dave Chinner" <david@fromorbit.com>,
        Christoph Hellwig <hch@lst.de>,
        "Theodore Y. Ts'o" <tytso@mit.edu>, Jan Kara <jack@suse.cz>,
        "linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>,
        "linux-xfs@vger.kernel.org" <linux-xfs@vger.kernel.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: RE: [RFC PATCH V2 09/12] fs: Prevent mode change if file is mmap'ed
Thread-Topic: [RFC PATCH V2 09/12] fs: Prevent mode change if file is mmap'ed
Thread-Index: AQHVx+xw3fI16+EnrkucPW5Ge+vrG6frihyw
Date:   Wed, 15 Jan 2020 10:21:45 +0000
Message-ID: <06258747f6824a35adfaa999ab4c2261@AcuMS.aculab.com>
References: <20200110192942.25021-1-ira.weiny@intel.com>
 <20200110192942.25021-10-ira.weiny@intel.com>
In-Reply-To: <20200110192942.25021-10-ira.weiny@intel.com>
Accept-Language: en-GB, en-US
Content-Language: en-US
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8BIT
Sender: linux-ext4-owner@vger.kernel.org
Precedence: bulk

From ira.weiny@intel.com
> Sent: 10 January 2020 19:30
> 
> Page faults need to ensure the inode mode is correct and consistent with
> the vmf information at the time of the fault.  There is no easy way to
> ensure the vmf information is correct if a mode change is in progress.
> Furthermore, there is no good use case to require a mode change while
> the file is mmap'ed.
> 
> Track mmap's of the file and fail the mode change if the file is
> mmap'ed.

This seems wrong to me.
I presume the 'mode changes' are from things like 'chmod -w ...'.
mmap() should be no different to open().
Only the permissions set when the file is opened count.

Next you'll be stopping unlink() when a file is open :-)

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)