Re: [PATCH] fuse: Move same-superblock check to fuse_copy_file_range

[Bernd Schubert <bernd@bsbernd.com>]

On 8/6/25 15:52, Chunsheng Luo wrote:
> The copy_file_range COPY_FILE_SPLICE capability allows filesystems to
> handle cross-superblock copy. However, in the current fuse implementation,
> __fuse_copy_file_range accesses src_file->private_data under the assumption
> that it points to a fuse_file structure. When the source file belongs to a
> non-FUSE filesystem, it will leads to kernel panics.
> 
> To resolve this, move the same-superblock check from __fuse_copy_file_range
> to fuse_copy_file_range to ensure both files belong to the same fuse
> superblock before accessing private_data.
> 
> Signed-off-by: Chunsheng Luo <luochunsheng@ustc.edu>
> ---
>  fs/fuse/file.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 95275a1e2f54..a29f1b84f11b 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -2984,9 +2984,6 @@ static ssize_t __fuse_copy_file_range(struct file *file_in, loff_t pos_in,
>  	if (fc->no_copy_file_range)
>  		return -EOPNOTSUPP;
>  
> -	if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
> -		return -EXDEV;
> -
>  	inode_lock(inode_in);
>  	err = fuse_writeback_range(inode_in, pos_in, pos_in + len - 1);
>  	inode_unlock(inode_in);
> @@ -3066,9 +3063,12 @@ static ssize_t fuse_copy_file_range(struct file *src_file, loff_t src_off,
>  {
>  	ssize_t ret;
>  
> +	if (file_inode(src_file)->i_sb != file_inode(dst_file)->i_sb)
> +		return splice_copy_file_range(src_file, src_off, dst_file,
> +					     dst_off, len);
> +
>  	ret = __fuse_copy_file_range(src_file, src_off, dst_file, dst_off,
>  				     len, flags);
> -
>  	if (ret == -EOPNOTSUPP || ret == -EXDEV)
>  		ret = splice_copy_file_range(src_file, src_off, dst_file,
>  					     dst_off, len);

I guess you can remove the check EXDEV here?