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Commit 8135be5a authored by Vladimir Davydov's avatar Vladimir Davydov Committed by Linus Torvalds
Browse files

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: default avatarVladimir Davydov <vdavydov@parallels.com>
Acked-by: default avatarChristoph Lameter <cl@linux.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ae6e71d3

include/linux/memcontrol.h

+12 −2
Original line number Diff line number Diff line
@@ -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 */

include/linux/slab.h

+0 −2
Original line number Diff line number Diff line
@@ -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;

		};

	};

};

mm/memcontrol.c

+16 −35
Original line number Diff line number Diff line
@@ -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)
@@ -2705,8 +2701,6 @@ 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);

	}

	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);

}

mm/slab.c

+2 −0
Original line number Diff line number Diff line
@@ -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;

}

mm/slub.c

+9 −5
Original line number Diff line number Diff line
@@ -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