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From: Mark Fasheh <mfasheh@suse.de>
To: Adam Borowski <kilobyte@angband.pl>
Cc: linux-fsdevel@vger.kernel.org, linux-btrfs@vger.kernel.org,
	linux-xfs@vger.kernel.org
Subject: Re: [PATCH 1/2] vfs: allow dedupe of user owned read-only files
Date: Fri, 18 May 2018 01:01:50 +0200	[thread overview]
Message-ID: <20180517230150.GA28045@wotan.suse.de> (raw)
In-Reply-To: <20180513205025.3kolgcnbpy4grqtv@angband.pl>

On Sun, May 13, 2018 at 10:50:25PM +0200, Adam Borowski wrote:
> On Sun, May 13, 2018 at 06:16:53PM +0000, Mark Fasheh wrote:
> > On Sat, May 12, 2018 at 04:49:20AM +0200, Adam Borowski wrote:
> > > On Fri, May 11, 2018 at 12:26:50PM -0700, Mark Fasheh wrote:
> > > > The permission check in vfs_dedupe_file_range() is too coarse - We
> > > > only allow dedupe of the destination file if the user is root, or
> > > > they have the file open for write.
> > > > 
> > > > This effectively limits a non-root user from deduping their own
> > > > read-only files. As file data during a dedupe does not change,
> > > > this is unexpected behavior and this has caused a number of issue
> > > > reports.
> [...]
> > > > So change the check so we allow dedupe on the target if:
> > > > 
> > > > - the root or admin is asking for it
> > > > - the owner of the file is asking for the dedupe
> > > > - the process has write access
> > > 
> > > I submitted a similar patch in May 2016, yet it has never been applied
> > > despite multiple pings, with no NAK.  My version allowed dedupe if:
> > > - the root or admin is asking for it
> > > - the file has w permission (on the inode -- ie, could have been opened rw)
> > 
> > Ahh, yes I see that now. I did wind up acking it too :)
> > > 
> > > I like this new version better than mine: "root or owner or w" is more
> > > Unixy than "could have been opened w".
> > 
> > I agree, IMHO the behavior in this patch is intuitive. What we had before
> > would surprise users.
> 
> Actually, there's one reason to still consider "could have been opened w":
> with it, deduplication programs can simply open the file r and not care
> about ETXTBSY at all.  Otherwise, every program needs to stat() and have
> logic to pick the proper argument to the open() call (r if owner/root,
> rw or w if not).

That makes sense. The goal after all is to be able to just open r and not
worry about it. I hadn't considered the other possibilities that
inode_permission() covers. I'll make that change for my next series.

Thanks,
  --Mark

  reply	other threads:[~2018-05-17 23:01 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-11 19:26 [PATCH 0/2] vfs: better dedupe permission check Mark Fasheh
2018-05-11 19:26 ` [PATCH 1/2] vfs: allow dedupe of user owned read-only files Mark Fasheh
2018-05-11 23:58   ` Darrick J. Wong
2018-05-12  2:49   ` Adam Borowski
2018-05-13 18:16     ` Mark Fasheh
2018-05-13 20:50       ` Adam Borowski
2018-05-17 23:01         ` Mark Fasheh [this message]
2018-05-11 19:26 ` [PATCH 2/2] vfs: dedupe should return EPERM if permission is not granted Mark Fasheh
2018-05-12  0:06   ` Darrick J. Wong
2018-05-12  4:15     ` Amir Goldstein
2018-05-12  4:37     ` Duncan
2018-05-13 14:30     ` Adam Borowski
2018-05-13 18:21     ` Mark Fasheh
2018-05-13 18:26       ` Darrick J. Wong
2018-05-17  5:15         ` Zygo Blaxell
2018-05-17 23:03           ` Mark Fasheh
2018-05-14 14:58   ` David Sterba
2018-09-10 23:21 [PATCH v6 0/2] vfs: fix dedupe permission check Mark Fasheh
2018-09-10 23:21 ` [PATCH 1/2] vfs: allow dedupe of user owned read-only files Mark Fasheh

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