mm/damon/core: initialize damo_filter->list from damos_new_filter()

damos_new_filter() is not initializing the list field of newly allocated
filter object.  However, DAMON sysfs interface and DAMON_RECLAIM are not
initializing it after calling damos_new_filter().  As a result, accessing
uninitialized memory is possible.  Actually, adding multiple DAMOS filters
via DAMON sysfs interface caused NULL pointer dereferencing.  Initialize
the field just after the allocation from damos_new_filter().

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 98def23 ("mm/damon/core: implement damos filter")
Signed-off-by: SeongJae Park <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

mm/damon/core.c

@@ -273,6 +273,7 @@ struct damos_filter *damos_new_filter(enum damos_filter_type type,
 		return NULL;
 	filter->type = type;
 	filter->matching = matching;
+	INIT_LIST_HEAD(&filter->list);
 	return filter;
 }