Re: [PATCH v14] vfs: fix copy_file_range() regression in cross-fs copies

[Namjae Jeon <linkinjeon@kernel.org>]

2022-06-06 22:46 GMT+09:00, Amir Goldstein <amir73il@gmail.com>:
> From: Luis Henriques <lhenriques@suse.de>
>
> 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.
>
> Another regression has been reported by He Zhe - the assertion of
> WARN_ON_ONCE(ret == -EOPNOTSUPP) can be triggered from userspace when
> copying from a sysfs file whose read operation may return -EOPNOTSUPP.
>
> Since we do not have test coverage for copy_file_range() between any
> two types of filesystems, the best way to avoid these sort of issues
> in the future is for the kernel to be more picky about filesystems that
> are allowed to do copy_file_range().
>
> This patch restores some cross-filesystem copy restrictions that existed
> prior to commit 5dae222a5ff0 ("vfs: allow copy_file_range to copy across
> devices"), namely, cross-sb copy is not allowed for filesystems that do
> not implement ->copy_file_range().
>
> Filesystems that do implement ->copy_file_range() have full control of
> the result - if this method returns an error, the error is returned to
> the user.  Before this change this was only true for fs that did not
> implement the ->remap_file_range() operation (i.e. nfsv3).
>
> Filesystems that implement only ->remap_file_range() (i.e. xfs) may still
> fall-back to the generic_copy_file_range() implementation when the copy
> is within the same sb, but filesystem cannot handle the reuqested copied
> range.  This helps the kernel can maintain a more consistent story about
> which filesystems support copy_file_range().
>
> nfsd and ksmbd servers are modified to fall-back to the
> generic_copy_file_range() implementation in case vfs_copy_file_range()
> fails with -EOPNOTSUPP or -EXDEV, which preserves behavior of
> server-side-copy.
>
> fall-back to generic_copy_file_range() is not implemented for the smb
> operation FSCTL_DUPLICATE_EXTENTS_TO_FILE, which is arguably a correct
> change of behavior.
>
> Fixes: 5dae222a5ff0 ("vfs: allow copy_file_range to copy across devices")
> Link:
> https://lore.kernel.org/linux-fsdevel/20210212044405.4120619-1-drinkcat@chromium.org/
> Link:
> https://lore.kernel.org/linux-fsdevel/CANMq1KDZuxir2LM5jOTm0xx+BnvW=ZmpsG47CyHFJwnw7zSX6Q@mail.gmail.com/
> Link:
> https://lore.kernel.org/linux-fsdevel/20210126135012.1.If45b7cdc3ff707bc1efa17f5366057d60603c45f@changeid/
> Link:
> https://lore.kernel.org/linux-fsdevel/20210630161320.29006-1-lhenriques@suse.de/
> Reported-by: Nicolas Boichat <drinkcat@chromium.org>
> Reported-by: kernel test robot <oliver.sang@intel.com>
> Signed-off-by: Luis Henriques <lhenriques@suse.de>
> Fixes: 64bf5ff58dff ("vfs: no fallback for ->copy_file_range")
> Link:
> https://lore.kernel.org/linux-fsdevel/20f17f64-88cb-4e80-07c1-85cb96c83619@windriver.com/
> Reported-by: He Zhe <zhe.he@windriver.com>
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> ---
>
> Hi Steve, Namje,
>
> I was going to ping Al about this patch when I remembered that we have
> another kernel file server that supports server side copy and needs to
> be adjusted. I also realized that v13 wrongly (?) falls back to
> generic_copy_file_range() in nfs/smb client code.
>
> It would be great if you could review my ksmbd change and run the fstests
> as below in your test setup.
I have run xfstests against ksmbd. All tests are passed.
You can add my tags for ksmbd.

Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Tested-by: Namjae Jeon <linkinjeon@kernel.org>

Thanks!