mm/slab_common: fix possible double free of kmem_cache

When doing slub_debug test, kfence's 'test_memcache_typesafe_by_rcu'
kunit test case cause a use-after-free error:

  BUG: KASAN: use-after-free in kobject_del+0x14/0x30
  Read of size 8 at addr ffff888007679090 by task kunit_try_catch/261

  CPU: 1 PID: 261 Comm: kunit_try_catch Tainted: G    B            N 6.0.0-rc5-next-20220916 #17
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
  Call Trace:
   <TASK>
   dump_stack_lvl+0x34/0x48
   print_address_description.constprop.0+0x87/0x2a5
   print_report+0x103/0x1ed
   kasan_report+0xb7/0x140
   kobject_del+0x14/0x30
   kmem_cache_destroy+0x130/0x170
   test_exit+0x1a/0x30
   kunit_try_run_case+0xad/0xc0
   kunit_generic_run_threadfn_adapter+0x26/0x50
   kthread+0x17b/0x1b0
   </TASK>

The cause is inside kmem_cache_destroy():

kmem_cache_destroy
    acquire lock/mutex
    shutdown_cache
        schedule_work(kmem_cache_release) (if RCU flag set)
    release lock/mutex
    kmem_cache_release (if RCU flag not set)

In some certain timing, the scheduled work could be run before
the next RCU flag checking, which can then get a wrong value
and lead to double kmem_cache_release().

Fix it by caching the RCU flag inside protected area, just like 'refcnt'

Fixes: 0495e337b703 ("mm/slab_common: Deleting kobject in kmem_cache_destroy() without holding slab_mutex/cpu_hotplug_lock")
Signed-off-by: Feng Tang <feng.tang@intel.com>
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Reviewed-by: Waiman Long <longman@redhat.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 07b948288f84d2bff32289d662846f941cde0761..ccc02573588f843f2da0d5c8ec128c2ad2bcbd88 100644 (file)
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -475,6 +475,7 @@ void slab_kmem_cache_release(struct kmem_cache *s)
 void kmem_cache_destroy(struct kmem_cache *s)
 {
        int refcnt;
+       bool rcu_set;
 
        if (unlikely(!s) || !kasan_check_byte(s))
                return;
@@ -482,6 +483,8 @@ void kmem_cache_destroy(struct kmem_cache *s)
        cpus_read_lock();
        mutex_lock(&slab_mutex);
 
+       rcu_set = s->flags & SLAB_TYPESAFE_BY_RCU;
+
        refcnt = --s->refcount;
        if (refcnt)
                goto out_unlock;
@@ -492,7 +495,7 @@ void kmem_cache_destroy(struct kmem_cache *s)
 out_unlock:
        mutex_unlock(&slab_mutex);
        cpus_read_unlock();
-       if (!refcnt && !(s->flags & SLAB_TYPESAFE_BY_RCU))
+       if (!refcnt && !rcu_set)
                kmem_cache_release(s);
 }
 EXPORT_SYMBOL(kmem_cache_destroy);