dax/fsdev: fix uninitialized kaddr in fsdev_dax_zero_page_range()

__fsdev_dax_direct_access() returns -EFAULT without setting *kaddr when
dax_pgoff_to_phys() returns -1 (pgoff out of range). The return value
was ignored, leaving kaddr uninitialized before being passed to
fsdev_write_dax().

Check the return value and propagate the error.

Thanks to Dan Carpenter and the smatch project for reporting this.

Signed-off-by: John Groves <[email protected]>
Reviewed-by: Jonathan Cameron <[email protected]>
Reviewed-by: Dave Jiang <[email protected]>
Link: https://patch.msgid.link/0100019d8262cda2-9714d31c-8fc1-4ca5-b32d-4df678240d14-000000@email.amazonses.com
Signed-off-by: Ira Weiny <[email protected]>

Author: jagalactic

drivers/dax/fsdev.c

@@ -80,9 +80,12 @@ static int fsdev_dax_zero_page_range(struct dax_device *dax_dev,
 			pgoff_t pgoff, size_t nr_pages)
 {
 	void *kaddr;
+	long rc;
 
 	WARN_ONCE(nr_pages > 1, "%s: nr_pages > 1\n", __func__);
-	__fsdev_dax_direct_access(dax_dev, pgoff, 1, DAX_ACCESS, &kaddr, NULL);
+	rc = __fsdev_dax_direct_access(dax_dev, pgoff, 1, DAX_ACCESS, &kaddr, NULL);
+	if (rc < 0)
+		return rc;
 	fsdev_write_dax(kaddr, ZERO_PAGE(0), 0, PAGE_SIZE);
 	return 0;
 }