On Wed, 4 Mar 2020, Jann Horn wrote: > Hi! > > FYI, I noticed that if you do something like the following as root, > the system blows up pretty quickly with error messages about stuff > like corrupt freelist pointers because SLUB actually allows root to > force a page order that is smaller than what is required to store a > single object: > > echo 0 > /sys/kernel/slab/task_struct/order > > The other SLUB debugging options, like red_zone, also look kind of > suspicious with regards to races (either racing with other writes to > the SLUB debugging options, or with object allocations). > Thanks for the report, Jann. To address the most immediate issue, allowing a smaller order than allowed, I think we'd need something like this. I can propose it as a formal patch if nobody has any alternate suggestions? --- mm/slub.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/slub.c b/mm/slub.c --- a/mm/slub.c +++ b/mm/slub.c @@ -3598,7 +3598,7 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order) */ size = ALIGN(size, s->align); s->size = size; - if (forced_order >= 0) + if (forced_order >= slab_order(size, 1, MAX_ORDER, 1)) order = forced_order; else order = calculate_order(size);
