NACK[F]/Cmnt: [SRU][L/K/J/F][PATCH 0/1] UBUNTU: SAUCE: overlayfs: fix reference count mismatch

[Andrea Righi]

On Fri, Jun 30, 2023 at 09:26:20AM +0200, Stefan Bader wrote:
> On 22.06.23 11:37, Andrea Righi wrote:
> > BugLink: https://bugs.launchpad.net/bugs/2016398
> > 
> > [Impact]
> > 
> > Opened files reported in /proc/pid/map_files can be shows with the wrong
> > mount point using overlayfs with filesystem namspaces.
> > 
> > This incorrect behavior is fixed:
> > 
> >    UBUNTU: SAUCE: overlayfs: fix incorrect mnt_id of files opened from map_files
> > 
> > However, the fix introduced a new regression, the reference to the
> > original file stored in vma->vm_prfile is not properly released when
> > vma->vm_prfile is replaced with a new file.
> > 
> > This can cause a reference counter unbalance, leading errors such as
> > "target is busy" when trying to unmount overlayfs, even if the
> > filesystem has not active reference.
> > 
> > [Test case]
> > 
> > Reproducer provided by original bug reporter:
> > https://launchpadlibrarian.net/663151659/overlayfsscript_example
> > 
> > [Fix]
> > 
> > Fix by properly releasing the original file stored in vm_prfile.
> > 
> > [Regression potential]
> > 
> > This fix seems to solve the reported bug (verified with the reproducer)
> > and it doesn't seem to introduce other regressions or behavior change.
> > 
> > However, we may experience regressions in overlayfs or potentially other
> > "target is busy" errors when unmounting overlayfs filesystems with this
> > fix applied, if there are still other corner cases not covered properly.
> > 
> > 
> 
> From the discussion I would expect a fresh submission for Focal. Andrea, I
> think that would better be a new thread. Hence the NACK.

Yes, I'll send a new patch set in a separate thread. Thanks!

-Andrea