Hey Adam, 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. For an example, see: > > > > https://github.com/markfasheh/duperemove/issues/129 > > > > 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 :) > There was a request to include in xfstests a test case for the ETXTBSY race > this patch fixes, but there's no reasonable way to make such a test case: > the race condition is not a bug, it's write-xor-exec working as designed. > > Another idea discussed was about possibly just allowing everyone who can > open the file to deduplicate it, as the file contents are not modified in > any way. Zygo Blaxell expressed a concern that it could be used by an > unprivileged user who can trigger a crash to abuse writeout bugs. > > 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. Yeah we've been careful about not letting a user dedupe some other users file. Data-wise it technically might be ok but I can imagine several scenarios where you might not want some other user deduping your files. Thanks for the review, --Mark
