The patch titled
Subject: kasan: drain quarantine of memcg slab objects
has been added to the -mm tree. Its filename is
kasan-drain-quarantine-of-memcg-slab-objects.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/kasan-drain-quarantine-of-memcg-slab-objects.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/kasan-drain-quarantine-of-memcg-slab-objects.patch
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From: Greg Thelen <gthelen@xxxxxxxxxx>
Subject: kasan: drain quarantine of memcg slab objects
Per memcg slab accounting and kasan have a problem with kmem_cache
destruction.
- kmem_cache_create() allocates a kmem_cache, which is used for
allocations from processes running in root (top) memcg.
- Processes running in non root memcg and allocating with either
__GFP_ACCOUNT or from a SLAB_ACCOUNT cache use a per memcg kmem_cache.
- Kasan catches use-after-free by having kfree() and kmem_cache_free()
defer freeing of objects. Objects are placed in a quarantine.
- kmem_cache_destroy() destroys root and non root kmem_caches. It takes
care to drain the quarantine of objects from the root memcg's
kmem_cache, but ignores objects associated with non root memcg. This
causes leaks because quarantined per memcg objects refer to per memcg
kmem cache being destroyed.
To see the problem:
1) create a slab cache with kmem_cache_create(,,,SLAB_ACCOUNT,)
2) from non root memcg, allocate and free a few objects from cache
3) dispose of the cache with kmem_cache_destroy()
kmem_cache_destroy() will trigger a "Slab cache still has objects"
warning indicating that the per memcg kmem_cache structure was leaked.
Fix the leak by draining kasan quarantined objects allocated from non
root memcg.
Racing memcg deletion is tricky, but handled. kmem_cache_destroy() =>
shutdown_memcg_caches() => __shutdown_memcg_cache() => shutdown_cache()
flushes per memcg quarantined objects, even if that memcg has been
rmdir'd and gone through memcg_deactivate_kmem_caches().
This leak only affects destroyed SLAB_ACCOUNT kmem caches when kasan is
enabled. So I don't think it's worth patching stable kernels.
Link: http://lkml.kernel.org/r/1482257462-36948-1-git-send-email-gthelen@xxxxxxxxxx
Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/kasan.h | 4 ++--
mm/kasan/kasan.c | 2 +-
mm/kasan/quarantine.c | 1 +
mm/slab_common.c | 4 +++-
4 files changed, 7 insertions(+), 4 deletions(-)
diff -puN include/linux/kasan.h~kasan-drain-quarantine-of-memcg-slab-objects include/linux/kasan.h
--- a/include/linux/kasan.h~kasan-drain-quarantine-of-memcg-slab-objects
+++ a/include/linux/kasan.h
@@ -52,7 +52,7 @@ void kasan_free_pages(struct page *page,
void kasan_cache_create(struct kmem_cache *cache, size_t *size,
unsigned long *flags);
void kasan_cache_shrink(struct kmem_cache *cache);
-void kasan_cache_destroy(struct kmem_cache *cache);
+void kasan_cache_shutdown(struct kmem_cache *cache);
void kasan_poison_slab(struct page *page);
void kasan_unpoison_object_data(struct kmem_cache *cache, void *object);
@@ -98,7 +98,7 @@ static inline void kasan_cache_create(st
size_t *size,
unsigned long *flags) {}
static inline void kasan_cache_shrink(struct kmem_cache *cache) {}
-static inline void kasan_cache_destroy(struct kmem_cache *cache) {}
+static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
static inline void kasan_poison_slab(struct page *page) {}
static inline void kasan_unpoison_object_data(struct kmem_cache *cache,
diff -puN mm/kasan/kasan.c~kasan-drain-quarantine-of-memcg-slab-objects mm/kasan/kasan.c
--- a/mm/kasan/kasan.c~kasan-drain-quarantine-of-memcg-slab-objects
+++ a/mm/kasan/kasan.c
@@ -435,7 +435,7 @@ void kasan_cache_shrink(struct kmem_cach
quarantine_remove_cache(cache);
}
-void kasan_cache_destroy(struct kmem_cache *cache)
+void kasan_cache_shutdown(struct kmem_cache *cache)
{
quarantine_remove_cache(cache);
}
diff -puN mm/kasan/quarantine.c~kasan-drain-quarantine-of-memcg-slab-objects mm/kasan/quarantine.c
--- a/mm/kasan/quarantine.c~kasan-drain-quarantine-of-memcg-slab-objects
+++ a/mm/kasan/quarantine.c
@@ -274,6 +274,7 @@ static void per_cpu_remove_cache(void *a
qlist_free_all(&to_free, cache);
}
+/* Free all quarantined objects belonging to cache. */
void quarantine_remove_cache(struct kmem_cache *cache)
{
unsigned long flags, i;
diff -puN mm/slab_common.c~kasan-drain-quarantine-of-memcg-slab-objects mm/slab_common.c
--- a/mm/slab_common.c~kasan-drain-quarantine-of-memcg-slab-objects
+++ a/mm/slab_common.c
@@ -461,6 +461,9 @@ EXPORT_SYMBOL(kmem_cache_create);
static int shutdown_cache(struct kmem_cache *s,
struct list_head *release, bool *need_rcu_barrier)
{
+ /* free asan quarantined objects */
+ kasan_cache_shutdown(s);
+
if (__kmem_cache_shutdown(s) != 0)
return -EBUSY;
@@ -744,7 +747,6 @@ void kmem_cache_destroy(struct kmem_cach
get_online_cpus();
get_online_mems();
- kasan_cache_destroy(s);
mutex_lock(&slab_mutex);
s->refcount--;
_
Patches currently in -mm which might be from gthelen@xxxxxxxxxx are
kasan-drain-quarantine-of-memcg-slab-objects.patch
kasan-add-memcg-kmem_cache-test.patch
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