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Date:   Mon, 7 Dec 2020 10:06:32 +0800
From:   Kuan-Ying Lee <Kuan-Ying.Lee@...iatek.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     "qiang.zhang@...driver.com" <qiang.zhang@...driver.com>,
        "sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
        "aryabinin@...tuozzo.com" <aryabinin@...tuozzo.com>,
        "dvyukov@...gle.com" <dvyukov@...gle.com>,
        "andreyknvl@...gle.com" <andreyknvl@...gle.com>,
        "qcai@...hat.com" <qcai@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        <walter-zh.wu@...iatek.com>
Subject: Re: [PATCH] kasan: fix slab double free when cpu-hotplug

On Sat, 2020-12-05 at 17:09 -0800, Andrew Morton wrote:
> On Sun, 6 Dec 2020 00:17:15 +0800 Kuan-Ying Lee <Kuan-Ying.Lee@...iatek.com> wrote:
> 
> > On Fri, 2020-12-04 at 17:25 -0800, Andrew Morton wrote:
> > > On Fri, 4 Dec 2020 20:01:35 +0800 Kuan-Ying Lee <Kuan-Ying.Lee@...iatek.com> wrote:
> > > 
> > > > > diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
> > > > > index d98b516f372f..55783125a767 100644
> > > > > --- a/mm/kasan/quarantine.c
> > > > > +++ b/mm/kasan/quarantine.c
> > > > > @@ -194,7 +194,6 @@ bool quarantine_put(struct kmem_cache *cache, void *object)
> > > > >  
> > > > >  	q = this_cpu_ptr(&cpu_quarantine);
> > > > >  	if (q->offline) {
> > > > > -		qlink_free(&meta->quarantine_link, cache);
> > > > >  		local_irq_restore(flags);
> > > > >  		return false;
> > 
> > Hi Andrew,
> > 
> > Return false will cause slab allocator to free the object.
> > Thus, we do not need to qlink_free here to free object twice.
> > 
> > The return value is introduced from Andrey's patch.
> > "kasan: sanitize objects when metadata doesn't fit"
> > 
> > 
> > > > >  	}
> > > > 
> > > > Hi Qiang,
> > > > 
> > > > Thanks for fixing this.
> > > > Due to that issue, my commit has been removed by Stephen from
> > > > linux-next.
> > > > 
> > > > 
> > > > Hi Stephen, Andrew,
> > > > 
> > > > Should I directly upload the v4 or Stephen can pick the commit which 
> > > > has been removed back to the linux-next.
> > > 
> > > I took care of it.  Restored the original patch and added this one as a
> > > -fix.
> > 
> > Thanks for taking care of it.
> > 
> > I think there are some problem in the patch you just restored.
> > I saw the restored patch is not based on Andrey's patch and Stephen's
> > fix conflict patch.
> > 
> > But the issue Qiang fixed need to be based on the Andrey's patch and
> > Stephen's fix conflict patch.
> > "kasan: sanitize objects when metadata doesn't fit"
> > "kasan-rename-get_alloc-free_info-fix"
> > 
> > If the restored patch is not based on that, it may cause some problems
> > and conflicts.
> > 
> > I think I can prepare a patch v4 based on Andrey's patch, fix the
> > conflict and include the Qiang's modification.
> 
> I'm not sure what you mean here.  When appying this fix, yes, I had to
> replace "meta" with "info", of course.
> 
> So the combined patch, which I'd like to send to Linus next week is as
> below.  Is there something wrong with it?
> 

Is this combined patch based on Andrey's patch?

If yes, Andrey's patch not only change the "info" to "meta" but also
introduce the return value.
I think we need to add return value or it will build error.

> 
> From: Kuan-Ying Lee <Kuan-Ying.Lee@...iatek.com>
> Subject: kasan: fix object remaining in offline per-cpu quarantine
> 
> We hit this issue in our internal test.  When enabling generic kasan, a
> kfree()'d object is put into per-cpu quarantine first.  If the cpu goes
> offline, object still remains in the per-cpu quarantine.  If we call
> kmem_cache_destroy() now, slub will report "Objects remaining" error.
> 
> [   74.982625] =============================================================================
> [   74.983380] BUG test_module_slab (Not tainted): Objects remaining in test_module_slab on __kmem_cache_shutdown()
> [   74.984145] -----------------------------------------------------------------------------
> [   74.984145]
> [   74.984883] Disabling lock debugging due to kernel taint
> [   74.985561] INFO: Slab 0x(____ptrval____) objects=34 used=1 fp=0x(____ptrval____) flags=0x2ffff00000010200
> [   74.986638] CPU: 3 PID: 176 Comm: cat Tainted: G    B             5.10.0-rc1-00007-g4525c8781ec0-dirty #10
> [   74.987262] Hardware name: linux,dummy-virt (DT)
> [   74.987606] Call trace:
> [   74.987924]  dump_backtrace+0x0/0x2b0
> [   74.988296]  show_stack+0x18/0x68
> [   74.988698]  dump_stack+0xfc/0x168
> [   74.989030]  slab_err+0xac/0xd4
> [   74.989346]  __kmem_cache_shutdown+0x1e4/0x3c8
> [   74.989779]  kmem_cache_destroy+0x68/0x130
> [   74.990176]  test_version_show+0x84/0xf0
> [   74.990679]  module_attr_show+0x40/0x60
> [   74.991218]  sysfs_kf_seq_show+0x128/0x1c0
> [   74.991656]  kernfs_seq_show+0xa0/0xb8
> [   74.992059]  seq_read+0x1f0/0x7e8
> [   74.992415]  kernfs_fop_read+0x70/0x338
> [   74.993051]  vfs_read+0xe4/0x250
> [   74.993498]  ksys_read+0xc8/0x180
> [   74.993825]  __arm64_sys_read+0x44/0x58
> [   74.994203]  el0_svc_common.constprop.0+0xac/0x228
> [   74.994708]  do_el0_svc+0x38/0xa0
> [   74.995088]  el0_sync_handler+0x170/0x178
> [   74.995497]  el0_sync+0x174/0x180
> [   74.996050] INFO: Object 0x(____ptrval____) @offset=15848
> [   74.996752] INFO: Allocated in test_version_show+0x98/0xf0 age=8188 cpu=6 pid=172
> [   75.000802]  stack_trace_save+0x9c/0xd0
> [   75.002420]  set_track+0x64/0xf0
> [   75.002770]  alloc_debug_processing+0x104/0x1a0
> [   75.003171]  ___slab_alloc+0x628/0x648
> [   75.004213]  __slab_alloc.isra.0+0x2c/0x58
> [   75.004757]  kmem_cache_alloc+0x560/0x588
> [   75.005376]  test_version_show+0x98/0xf0
> [   75.005756]  module_attr_show+0x40/0x60
> [   75.007035]  sysfs_kf_seq_show+0x128/0x1c0
> [   75.007433]  kernfs_seq_show+0xa0/0xb8
> [   75.007800]  seq_read+0x1f0/0x7e8
> [   75.008128]  kernfs_fop_read+0x70/0x338
> [   75.008507]  vfs_read+0xe4/0x250
> [   75.008990]  ksys_read+0xc8/0x180
> [   75.009462]  __arm64_sys_read+0x44/0x58
> [   75.010085]  el0_svc_common.constprop.0+0xac/0x228
> [   75.011006] kmem_cache_destroy test_module_slab: Slab cache still has objects
> 
> Register a cpu hotplug function to remove all objects in the offline
> per-cpu quarantine when cpu is going offline.  Set a per-cpu variable to
> indicate this cpu is offline.
> 
> [qiang.zhang@...driver.com: fix slab double free when cpu-hotplug]
>   Link: https://lkml.kernel.org/r/20201204102206.20237-1-qiang.zhang@windriver.com
> Link: https://lkml.kernel.org/r/1606895585-17382-2-git-send-email-Kuan-Ying.Lee@mediatek.com
> Signed-off-by: Kuan-Ying Lee <Kuan-Ying.Lee@...iatek.com>
> Signed-off-by: Zqiang <qiang.zhang@...driver.com>
> Suggested-by: Dmitry Vyukov <dvyukov@...gle.com>
> Reported-by: Guangye Yang <guangye.yang@...iatek.com>
> Reviewed-by: Dmitry Vyukov <dvyukov@...gle.com>
> Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
> Cc: Alexander Potapenko <glider@...gle.com>
> Cc: Matthias Brugger <matthias.bgg@...il.com>
> Cc: Nicholas Tang <nicholas.tang@...iatek.com>
> Cc: Miles Chen <miles.chen@...iatek.com>
> Cc: Qian Cai <qcai@...hat.com>
> Cc: Stephen Rothwell <sfr@...b.auug.org.au>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---
> 
>  mm/kasan/quarantine.c |   39 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 39 insertions(+)
> 
> --- a/mm/kasan/quarantine.c~kasan-fix-object-remain-in-offline-per-cpu-quarantine
> +++ a/mm/kasan/quarantine.c
> @@ -29,6 +29,7 @@
>  #include <linux/srcu.h>
>  #include <linux/string.h>
>  #include <linux/types.h>
> +#include <linux/cpuhotplug.h>
>  
>  #include "../slab.h"
>  #include "kasan.h"
> @@ -43,6 +44,7 @@ struct qlist_head {
>  	struct qlist_node *head;
>  	struct qlist_node *tail;
>  	size_t bytes;
> +	bool offline;
>  };
>  
>  #define QLIST_INIT { NULL, NULL, 0 }
> @@ -188,6 +190,10 @@ void quarantine_put(struct kasan_free_me

Andrey's patch changes the return value from "void" to "bool".
We need to replace void with bool.

>  	local_irq_save(flags);
>  
>  	q = this_cpu_ptr(&cpu_quarantine);
> +	if (q->offline) {
> +		local_irq_restore(flags);
> +		return;

I think we need to return false here. Otherwise, it will lack return
value and cause build error.

> +	}
>  	qlist_put(q, &info->quarantine_link, cache->size);

This "info" may cause conflict because Andrey's patch has already
changed it to "meta".

Thanks.
Kuan-Ying

>  	if (unlikely(q->bytes > QUARANTINE_PERCPU_SIZE)) {
>  		qlist_move_all(q, &temp);
> @@ -328,3 +334,36 @@ void quarantine_remove_cache(struct kmem
>  
>  	synchronize_srcu(&remove_cache_srcu);
>  }
> +
> +static int kasan_cpu_online(unsigned int cpu)
> +{
> +	this_cpu_ptr(&cpu_quarantine)->offline = false;
> +	return 0;
> +}
> +
> +static int kasan_cpu_offline(unsigned int cpu)
> +{
> +	struct qlist_head *q;
> +
> +	q = this_cpu_ptr(&cpu_quarantine);
> +	/* Ensure the ordering between the writing to q->offline and
> +	 * qlist_free_all. Otherwise, cpu_quarantine may be corrupted
> +	 * by interrupt.
> +	 */
> +	WRITE_ONCE(q->offline, true);
> +	barrier();
> +	qlist_free_all(q, NULL);
> +	return 0;
> +}
> +
> +static int __init kasan_cpu_quarantine_init(void)
> +{
> +	int ret = 0;
> +
> +	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/kasan:online",
> +				kasan_cpu_online, kasan_cpu_offline);
> +	if (ret < 0)
> +		pr_err("kasan cpu quarantine register failed [%d]\n", ret);
> +	return ret;
> +}
> +late_initcall(kasan_cpu_quarantine_init);
> _
> 

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