[PATCH] mm/memcg: return value of the function mem_cgroup_from_css() is not checked

[Yizhuo]

Inside function mem_cgroup_wb_domain(), the pointer memcg
could be NULL via mem_cgroup_from_css(). However, this pointer is
not checked and directly dereferenced in the if statement,
which is potentially unsafe.

Signed-off-by: Yizhuo <yzhai...@ucr.edu>
---
 mm/memcontrol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 661f046ad318..bd84bdaed3b0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3665,7 +3665,7 @@ struct wb_domain *mem_cgroup_wb_domain(struct 
bdi_writeback *wb)
 {
        struct mem_cgroup *memcg = mem_cgroup_from_css(wb->memcg_css);
 
-       if (!memcg->css.parent)
+       if (!memcg || !memcg->css.parent)
                return NULL;
 
        return &memcg->cgwb_domain;
-- 
2.17.1