Re: [PATCH] kasan: fix slab double free when cpu-hotplug
From: Kuan-Ying Lee
Date: Sun Dec 06 2020 - 21:07:38 EST
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@xxxxxxxxxxxx> 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@xxxxxxxxxxxx> 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@xxxxxxxxxxxx>
> 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@xxxxxxxxxxxxx: fix slab double free when cpu-hotplug]
> Link: https://lkml.kernel.org/r/20201204102206.20237-1-qiang.zhang@xxxxxxxxxxxxx
> Link: https://lkml.kernel.org/r/1606895585-17382-2-git-send-email-Kuan-Ying.Lee@xxxxxxxxxxxx
> Signed-off-by: Kuan-Ying Lee <Kuan-Ying.Lee@xxxxxxxxxxxx>
> Signed-off-by: Zqiang <qiang.zhang@xxxxxxxxxxxxx>
> Suggested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Reported-by: Guangye Yang <guangye.yang@xxxxxxxxxxxx>
> Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> Cc: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Matthias Brugger <matthias.bgg@xxxxxxxxx>
> Cc: Nicholas Tang <nicholas.tang@xxxxxxxxxxxx>
> Cc: Miles Chen <miles.chen@xxxxxxxxxxxx>
> Cc: Qian Cai <qcai@xxxxxxxxxx>
> Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
>
> 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);
> _
>