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memcg: fix possible use-after-free in memcg_kmem_get_cache()

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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 <vdavydov@parallels.com>
Acked-by: Christoph 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Vladimir Davydov
2014-12-12 16:56:38 -08:00
committed by Linus Torvalds
parent ae6e71d3d9
commit 8135be5a80
5 changed files with 39 additions and 44 deletions
Download Patch File Download Diff File Expand all files Collapse all files

51
mm/memcontrol.c
View File

@@ -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);
}