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). I also have a sister patch: btrfs_ioctl_defrag wants the same change, for the very same reason. But, let's discuss dedupe first to avoid unnecessary round trips. Meow! -- ⢀⣴⠾⠻⢶⣦⠀ ⣾⠁⢰⠒⠀⣿⡁ ⢿⡄⠘⠷⠚⠋⠀ Certified airhead; got the CT scan to prove that! ⠈⠳⣄⠀⠀⠀⠀
