Re: [PATCH v10] vfs: fix copy_file_range regression in cross-fs copies

[Luis Henriques]

On Wed, Jun 30, 2021 at 05:56:34PM +0300, Amir Goldstein wrote:
> On Wed, Jun 30, 2021 at 4:44 PM Luis Henriques <lhenriques@xxxxxxx> wrote:
> >
> > A regression has been reported by Nicolas Boichat, found while using the
> > copy_file_range syscall to copy a tracefs file.  Before commit
> > 5dae222a5ff0 ("vfs: allow copy_file_range to copy across devices") the
> > kernel would return -EXDEV to userspace when trying to copy a file across
> > different filesystems.  After this commit, the syscall doesn't fail anymore
> > and instead returns zero (zero bytes copied), as this file's content is
> > generated on-the-fly and thus reports a size of zero.
> >
> > This patch restores some cross-filesystem copy restrictions that existed
> > prior to commit 5dae222a5ff0 ("vfs: allow copy_file_range to copy across
> > devices").  Filesystems are still allowed to fall-back to the VFS
> > generic_copy_file_range() implementation, but that has now to be done
> > explicitly.
> >
> > nfsd is also modified to fall-back into generic_copy_file_range() in case
> > vfs_copy_file_range() fails with -EOPNOTSUPP or -EXDEV.
> >
> > Fixes: 5dae222a5ff0 ("vfs: allow copy_file_range to copy across devices")
> > Link: https://lore.kernel.org/linux-fsdevel/20210212044405.4120619-1-drinkcat@xxxxxxxxxxxx/
> > Link: https://lore.kernel.org/linux-fsdevel/CANMq1KDZuxir2LM5jOTm0xx+BnvW=ZmpsG47CyHFJwnw7zSX6Q@xxxxxxxxxxxxxx/
> > Link: https://lore.kernel.org/linux-fsdevel/20210126135012.1.If45b7cdc3ff707bc1efa17f5366057d60603c45f@changeid/
> > Reported-by: Nicolas Boichat <drinkcat@xxxxxxxxxxxx>
> > Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> > Signed-off-by: Luis Henriques <lhenriques@xxxxxxx>
> > ---
> > Changes since v9
> > - the early return from the syscall when len is zero now checks if the
> >   filesystem is implemented, returning -EOPNOTSUPP if it is not and 0
> >   otherwise.  Issue reported by test robot.
> 
> What issue was reported?

Here's the link to my previous email:

https://lore.kernel.org/linux-fsdevel/877dk1zibo.fsf@xxxxxxx/

... which reminds me that I need to also send a patch to fix the fstest.
(Although the test as-is actually allowed to find this bug...)

Cheers,
--
Luís