| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Date: Mon, 15 Aug 2022 10:01:07 -0400
From: Waiman Long <longman@...hat.com>
To: Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc: Christoph Lameter <cl@...ux.com>,
Pekka Enberg <penberg@...nel.org>,
David Rientjes <rientjes@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Andrew Morton <akpm@...ux-foundation.org>,
Vlastimil Babka <vbabka@...e.cz>,
Roman Gushchin <roman.gushchin@...ux.dev>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] mm/slab_common: Deleting kobject in
kmem_cache_destroy() without holding slab_mutex/cpu_hotplug_lock
On 8/13/22 11:00, Hyeonggon Yoo wrote:
> On Fri, Aug 12, 2022 at 02:30:33PM -0400, Waiman Long wrote:
>> A circular locking problem is reported by lockdep due to the following
>> circular locking dependency.
>>
>> +--> cpu_hotplug_lock --> slab_mutex --> kn->active --+
>> | |
>> +-----------------------------------------------------+
>>
>> The forward cpu_hotplug_lock ==> slab_mutex ==> kn->active dependency
>> happens in
>>
>> kmem_cache_destroy(): cpus_read_lock(); mutex_lock(&slab_mutex);
>> ==> sysfs_slab_unlink()
>> ==> kobject_del()
>> ==> kernfs_remove()
>> ==> __kernfs_remove()
>> ==> kernfs_drain(): rwsem_acquire(&kn->dep_map, ...);
> Maybe you mean this?
>
> /* but everyone should wait for draining */
> wait_event(root->deactivate_waitq,
> atomic_read(&kn->active) == KN_DEACTIVATED_BIAS);
>
This is part of the kernfs_drain() operation. However, I am focusing on
the behavior of the pseudo lock that causes the lockdep splat in the
first place. That is why I am showcasing the rwsem_acquire() call here.
>> The backward kn->active ==> cpu_hotplug_lock dependency happens in
>>
>> kernfs_fop_write_iter(): kernfs_get_active();
>> ==> slab_attr_store()
>> ==> cpu_partial_store()
>> ==> flush_all(): cpus_read_lock()
>>
>> One way to break this circular locking chain is to avoid holding
>> cpu_hotplug_lock and slab_mutex while deleting the kobject in
>> sysfs_slab_unlink() which should be equivalent to doing a write_lock
>> and write_unlock pair of the kn->active virtual lock.
>>
>> Since the kobject structures are not protected by slab_mutex or the
>> cpu_hotplug_lock, we can certainly release those locks before doing
>> the delete operation.
>>
>> Move sysfs_slab_unlink() and sysfs_slab_release() to the newly
>> created kmem_cache_release() and call it outside the slab_mutex &
>> cpu_hotplug_lock critical sections. There will be a slight delay
>> in the deletion of sysfs files if kmem_cache_release() is called
>> indirectly from a work function.
>>
>> Signed-off-by: Waiman Long <longman@...hat.com>
>> ---
>>
>> [v3] Move sysfs_slab_unlink() out to kmem_cache_release() and move
>> schedule_work() back right after list_add_tail().
>>
>> mm/slab_common.c | 45 +++++++++++++++++++++++++++++----------------
>> 1 file changed, 29 insertions(+), 16 deletions(-)
>>
>> diff --git a/mm/slab_common.c b/mm/slab_common.c
>> index 17996649cfe3..07b948288f84 100644
>> --- a/mm/slab_common.c
>> +++ b/mm/slab_common.c
>> @@ -392,6 +392,28 @@ kmem_cache_create(const char *name, unsigned int size, unsigned int align,
>> }
>> EXPORT_SYMBOL(kmem_cache_create);
>>
>> +#ifdef SLAB_SUPPORTS_SYSFS
>> +/*
>> + * For a given kmem_cache, kmem_cache_destroy() should only be called
>> + * once or there will be a use-after-free problem. The actual deletion
>> + * and release of the kobject does not need slab_mutex or cpu_hotplug_lock
>> + * protection. So they are now done without holding those locks.
>> + *
>> + * Note that there will be a slight delay in the deletion of sysfs files
>> + * if kmem_cache_release() is called indrectly from a work function.
>> + */
>> +static void kmem_cache_release(struct kmem_cache *s)
>> +{
>> + sysfs_slab_unlink(s);
>> + sysfs_slab_release(s);
>> +}
>> +#else
>> +static void kmem_cache_release(struct kmem_cache *s)
>> +{
>> + slab_kmem_cache_release(s);
>> +}
>> +#endif
>> +
>> static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work)
>> {
>> LIST_HEAD(to_destroy);
>> @@ -418,11 +440,7 @@ static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work)
>> list_for_each_entry_safe(s, s2, &to_destroy, list) {
>> debugfs_slab_release(s);
>> kfence_shutdown_cache(s);
>> -#ifdef SLAB_SUPPORTS_SYSFS
>> - sysfs_slab_release(s);
>> -#else
>> - slab_kmem_cache_release(s);
>> -#endif
>> + kmem_cache_release(s);
>> }
>> }
>>
>> @@ -437,20 +455,11 @@ static int shutdown_cache(struct kmem_cache *s)
>> list_del(&s->list);
>>
>> if (s->flags & SLAB_TYPESAFE_BY_RCU) {
>> -#ifdef SLAB_SUPPORTS_SYSFS
>> - sysfs_slab_unlink(s);
>> -#endif
>> list_add_tail(&s->list, &slab_caches_to_rcu_destroy);
>> schedule_work(&slab_caches_to_rcu_destroy_work);
>> } else {
>> kfence_shutdown_cache(s);
>> debugfs_slab_release(s);
>> -#ifdef SLAB_SUPPORTS_SYSFS
>> - sysfs_slab_unlink(s);
>> - sysfs_slab_release(s);
>> -#else
>> - slab_kmem_cache_release(s);
>> -#endif
>> }
>>
>> return 0;
>> @@ -465,14 +474,16 @@ void slab_kmem_cache_release(struct kmem_cache *s)
>>
>> void kmem_cache_destroy(struct kmem_cache *s)
>> {
>> + int refcnt;
>> +
>> if (unlikely(!s) || !kasan_check_byte(s))
>> return;
>>
>> cpus_read_lock();
>> mutex_lock(&slab_mutex);
>>
>> - s->refcount--;
>> - if (s->refcount)
>> + refcnt = --s->refcount;
>> + if (refcnt)
>> goto out_unlock;
>>
>> WARN(shutdown_cache(s),
>> @@ -481,6 +492,8 @@ 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))
>> + kmem_cache_release(s);
>> }
>> EXPORT_SYMBOL(kmem_cache_destroy);
>>
>> --
>> 2.31.1
>>
> little bit complicated but looks good to me.
> Thank you for fixing this.
>
> Reviewed-by: Hyeonggon Yoo <42.hyeyoo@...il.com>
>
Thanks for the review.
Cheers,
Longman
Powered by blists - more mailing lists