On Wed 21-08-19 23:22:09, Yizhuo wrote: > 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.
Could you describe circumstances when this would happen? The code is this way for 5 years without any issues. Are we just lucky or something has changed recently to make this happen? > Signed-off-by: Yizhuo <[email protected]> > --- > 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 > -- Michal Hocko SUSE Labs
