fuse: update inode size after extending passthrough write

yangyun reported that libfuse test test_copy_file_range() copies zero
bytes from a newly written file when fuse passthrough is enabled.

The reason is that extending passthrough write is not updating the fuse
inode size and when vfs_copy_file_range() observes a zero size inode,
it returns without calling the filesystem copy_file_range() method.

Fix this by adjusting the fuse inode size after an extending passthrough
write.

This does not provide cache coherency of fuse inode attributes and
backing inode attributes, but it should prevent situations where fuse
inode size is too small, causing read/copy to be wrongly shortened.

Reported-by: yangyun <[email protected]>
Closes: libfuse/libfuse#1048
Fixes: 57e1176 ("fuse: implement read/write passthrough")
Signed-off-by: Amir Goldstein <[email protected]>
Signed-off-by: Miklos Szeredi <[email protected]>

Author: amir73il

fs/fuse/passthrough.c

@@ -22,7 +22,7 @@ static void fuse_passthrough_end_write(struct file *file, loff_t pos, ssize_t re
 {
 	struct inode *inode = file_inode(file);
 
-	fuse_invalidate_attr_mask(inode, FUSE_STATX_MODSIZE);
+	fuse_write_update_attr(inode, pos, ret);
 }
 
 ssize_t fuse_passthrough_read_iter(struct kiocb *iocb, struct iov_iter *iter)