From 8135be5a8012f4c7e95218563855e16c09a8271b Mon Sep 17 00:00:00 2001 From: Vladimir Davydov Date: Fri, 12 Dec 2014 16:56:38 -0800 Subject: [PATCH] memcg: fix possible use-after-free in memcg_kmem_get_cache() Suppose task @t that belongs to a memory cgroup @memcg is going to allocate an object from a kmem cache @c. The copy of @c corresponding to @memcg, @mc, is empty. Then if kmem_cache_alloc races with the memory cgroup destruction we can access the memory cgroup's copy of the cache after it was destroyed: CPU0 CPU1 ---- ---- [ current=@t @mc->memcg_params->nr_pages=0 ] kmem_cache_alloc(@c): call memcg_kmem_get_cache(@c); proceed to allocation from @mc: alloc a page for @mc: ... move @t from @memcg destroy @memcg: mem_cgroup_css_offline(@memcg): memcg_unregister_all_caches(@memcg): kmem_cache_destroy(@mc) add page to @mc We could fix this issue by taking a reference to a per-memcg cache, but that would require adding a per-cpu reference counter to per-memcg caches, which would look cumbersome. Instead, let's take a reference to a memory cgroup, which already has a per-cpu reference counter, in the beginning of kmem_cache_alloc to be dropped in the end, and move per memcg caches destruction from css offline to css free. As a side effect, per-memcg caches will be destroyed not one by one, but all at once when the last page accounted to the memory cgroup is freed. This doesn't sound as a high price for code readability though. Note, this patch does add some overhead to the kmem_cache_alloc hot path, but it is pretty negligible - it's just a function call plus a per cpu counter decrement, which is comparable to what we already have in memcg_kmem_get_cache. Besides, it's only relevant if there are memory cgroups with kmem accounting enabled. I don't think we can find a way to handle this race w/o it, because alloc_page called from kmem_cache_alloc may sleep so we can't flush all pending kmallocs w/o reference counting. Signed-off-by: Vladimir Davydov Acked-by: Christoph Lameter Cc: Johannes Weiner Cc: Michal Hocko Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/memcontrol.h | 14 +++++++++-- include/linux/slab.h | 2 -- mm/memcontrol.c | 51 ++++++++++++-------------------------- mm/slab.c | 2 ++ mm/slub.c | 14 +++++++---- 5 files changed, 39 insertions(+), 44 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index b74942a9e22f..7c95af8d552c 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -400,8 +400,8 @@ int memcg_cache_id(struct mem_cgroup *memcg); void memcg_update_array_size(int num_groups); -struct kmem_cache * -__memcg_kmem_get_cache(struct kmem_cache *cachep); +struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep); +void __memcg_kmem_put_cache(struct kmem_cache *cachep); int __memcg_charge_slab(struct kmem_cache *cachep, gfp_t gfp, int order); void __memcg_uncharge_slab(struct kmem_cache *cachep, int order); @@ -494,6 +494,12 @@ memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp) return __memcg_kmem_get_cache(cachep); } + +static __always_inline void memcg_kmem_put_cache(struct kmem_cache *cachep) +{ + if (memcg_kmem_enabled()) + __memcg_kmem_put_cache(cachep); +} #else #define for_each_memcg_cache_index(_idx) \ for (; NULL; ) @@ -528,6 +534,10 @@ memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp) { return cachep; } + +static inline void memcg_kmem_put_cache(struct kmem_cache *cachep) +{ +} #endif /* CONFIG_MEMCG_KMEM */ #endif /* _LINUX_MEMCONTROL_H */ diff --git a/include/linux/slab.h b/include/linux/slab.h index 8a2457d42fc8..9a139b637069 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -493,7 +493,6 @@ static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node) * @memcg: pointer to the memcg this cache belongs to * @list: list_head for the list of all caches in this memcg * @root_cache: pointer to the global, root cache, this cache was derived from - * @nr_pages: number of pages that belongs to this cache. */ struct memcg_cache_params { bool is_root_cache; @@ -506,7 +505,6 @@ struct memcg_cache_params { struct mem_cgroup *memcg; struct list_head list; struct kmem_cache *root_cache; - atomic_t nr_pages; }; }; }; diff --git a/mm/memcontrol.c b/mm/memcontrol.c index dac81b975996..05e1584750ac 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2635,7 +2635,6 @@ static void memcg_register_cache(struct mem_cgroup *memcg, if (!cachep) return; - css_get(&memcg->css); list_add(&cachep->memcg_params->list, &memcg->memcg_slab_caches); /* @@ -2669,9 +2668,6 @@ static void memcg_unregister_cache(struct kmem_cache *cachep) list_del(&cachep->memcg_params->list); kmem_cache_destroy(cachep); - - /* drop the reference taken in memcg_register_cache */ - css_put(&memcg->css); } int __memcg_cleanup_cache_params(struct kmem_cache *s) @@ -2705,9 +2701,7 @@ static void memcg_unregister_all_caches(struct mem_cgroup *memcg) mutex_lock(&memcg_slab_mutex); list_for_each_entry_safe(params, tmp, &memcg->memcg_slab_caches, list) { cachep = memcg_params_to_cache(params); - kmem_cache_shrink(cachep); - if (atomic_read(&cachep->memcg_params->nr_pages) == 0) - memcg_unregister_cache(cachep); + memcg_unregister_cache(cachep); } mutex_unlock(&memcg_slab_mutex); } @@ -2742,10 +2736,10 @@ static void __memcg_schedule_register_cache(struct mem_cgroup *memcg, struct memcg_register_cache_work *cw; cw = kmalloc(sizeof(*cw), GFP_NOWAIT); - if (cw == NULL) { - css_put(&memcg->css); + if (!cw) return; - } + + css_get(&memcg->css); cw->memcg = memcg; cw->cachep = cachep; @@ -2776,12 +2770,8 @@ static void memcg_schedule_register_cache(struct mem_cgroup *memcg, int __memcg_charge_slab(struct kmem_cache *cachep, gfp_t gfp, int order) { unsigned int nr_pages = 1 << order; - int res; - res = memcg_charge_kmem(cachep->memcg_params->memcg, gfp, nr_pages); - if (!res) - atomic_add(nr_pages, &cachep->memcg_params->nr_pages); - return res; + return memcg_charge_kmem(cachep->memcg_params->memcg, gfp, nr_pages); } void __memcg_uncharge_slab(struct kmem_cache *cachep, int order) @@ -2789,7 +2779,6 @@ void __memcg_uncharge_slab(struct kmem_cache *cachep, int order) unsigned int nr_pages = 1 << order; memcg_uncharge_kmem(cachep->memcg_params->memcg, nr_pages); - atomic_sub(nr_pages, &cachep->memcg_params->nr_pages); } /* @@ -2816,22 +2805,13 @@ struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep) if (current->memcg_kmem_skip_account) return cachep; - rcu_read_lock(); - memcg = mem_cgroup_from_task(rcu_dereference(current->mm->owner)); - + memcg = get_mem_cgroup_from_mm(current->mm); if (!memcg_kmem_is_active(memcg)) goto out; memcg_cachep = cache_from_memcg_idx(cachep, memcg_cache_id(memcg)); - if (likely(memcg_cachep)) { - cachep = memcg_cachep; - goto out; - } - - /* The corresponding put will be done in the workqueue. */ - if (!css_tryget_online(&memcg->css)) - goto out; - rcu_read_unlock(); + if (likely(memcg_cachep)) + return memcg_cachep; /* * If we are in a safe context (can wait, and not in interrupt @@ -2846,12 +2826,17 @@ struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep) * defer everything. */ memcg_schedule_register_cache(memcg, cachep); - return cachep; out: - rcu_read_unlock(); + css_put(&memcg->css); return cachep; } +void __memcg_kmem_put_cache(struct kmem_cache *cachep) +{ + if (!is_root_cache(cachep)) + css_put(&cachep->memcg_params->memcg->css); +} + /* * We need to verify if the allocation against current->mm->owner's memcg is * possible for the given order. But the page is not allocated yet, so we'll @@ -2914,10 +2899,6 @@ void __memcg_kmem_uncharge_pages(struct page *page, int order) memcg_uncharge_kmem(memcg, 1 << order); page->mem_cgroup = NULL; } -#else -static inline void memcg_unregister_all_caches(struct mem_cgroup *memcg) -{ -} #endif /* CONFIG_MEMCG_KMEM */ #ifdef CONFIG_TRANSPARENT_HUGEPAGE @@ -4188,6 +4169,7 @@ static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss) static void memcg_destroy_kmem(struct mem_cgroup *memcg) { + memcg_unregister_all_caches(memcg); mem_cgroup_sockets_destroy(memcg); } #else @@ -4797,7 +4779,6 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css) } spin_unlock(&memcg->event_list_lock); - memcg_unregister_all_caches(memcg); vmpressure_cleanup(&memcg->vmpressure); } diff --git a/mm/slab.c b/mm/slab.c index fee275b5b6b7..6042fe57cc60 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -3182,6 +3182,7 @@ slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid, memset(ptr, 0, cachep->object_size); } + memcg_kmem_put_cache(cachep); return ptr; } @@ -3247,6 +3248,7 @@ slab_alloc(struct kmem_cache *cachep, gfp_t flags, unsigned long caller) memset(objp, 0, cachep->object_size); } + memcg_kmem_put_cache(cachep); return objp; } diff --git a/mm/slub.c b/mm/slub.c index 765c5884d03d..fe4db9c17238 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1233,13 +1233,17 @@ static inline void kfree_hook(const void *x) kmemleak_free(x); } -static inline int slab_pre_alloc_hook(struct kmem_cache *s, gfp_t flags) +static inline struct kmem_cache *slab_pre_alloc_hook(struct kmem_cache *s, + gfp_t flags) { flags &= gfp_allowed_mask; lockdep_trace_alloc(flags); might_sleep_if(flags & __GFP_WAIT); - return should_failslab(s->object_size, flags, s->flags); + if (should_failslab(s->object_size, flags, s->flags)) + return NULL; + + return memcg_kmem_get_cache(s, flags); } static inline void slab_post_alloc_hook(struct kmem_cache *s, @@ -1248,6 +1252,7 @@ static inline void slab_post_alloc_hook(struct kmem_cache *s, flags &= gfp_allowed_mask; kmemcheck_slab_alloc(s, flags, object, slab_ksize(s)); kmemleak_alloc_recursive(object, s->object_size, 1, s->flags, flags); + memcg_kmem_put_cache(s); } static inline void slab_free_hook(struct kmem_cache *s, void *x) @@ -2384,10 +2389,9 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s, struct page *page; unsigned long tid; - if (slab_pre_alloc_hook(s, gfpflags)) + s = slab_pre_alloc_hook(s, gfpflags); + if (!s) return NULL; - - s = memcg_kmem_get_cache(s, gfpflags); redo: /* * Must read kmem_cache cpu data via this cpu ptr. Preemption is -- 2.20.1