f2fs: allow copying file range only in between regular files

Only if two input files are regular files, we allow copying data in
range of them, otherwise, deny it.

Signed-off-by: Chao Yu <[e-mail]>
Signed-off-by: Jaegeuk Kim <[e-mail]>

fs/f2fs/file.c

···
 	if (unlikely(f2fs_readonly(src->i_sb)))
 		return -EROFS;
 
-	if (S_ISDIR(src->i_mode) || S_ISDIR(dst->i_mode))
-		return -EISDIR;
+	if (!S_ISREG(src->i_mode) || !S_ISREG(dst->i_mode))
+		return -EINVAL;
 
 	if (f2fs_encrypted_inode(src) || f2fs_encrypted_inode(dst))
 		return -EOPNOTSUPP;