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/20230729203733.38949-2-sj@kernel.org
Fixes: 98def236 ("mm/damon/core: implement damos filter")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>