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.
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