From: Alexander Potapenko <glider@google.com>
To: Walter Wu <walter-zh.wu@mediatek.com>
Cc: Kate Stewart <kstewart@linuxfoundation.org>,
wsd_upstream <wsd_upstream@mediatek.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-mediatek@lists.infradead.org,
linux-arm-kernel@lists.infradead.org,
Josh Poimboeuf <jpoimboe@redhat.com>,
Matthias Brugger <matthias.bgg@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
Dmitry Vyukov <dvyukov@google.com>
Subject: Re: [PATCH v3] lib/stackdepot: Fix global out-of-bounds in stackdepot
Date: Thu, 30 Jan 2020 13:03:58 +0100 [thread overview]
Message-ID: <CAG_fn=X_jSUJXD932z9oN5hBa--n3Qct4zrjzGaPtb2MwJye7A@mail.gmail.com> (raw)
In-Reply-To: <20200130064430.17198-1-walter-zh.wu@mediatek.com>
On Thu, Jan 30, 2020 at 7:44 AM Walter Wu <walter-zh.wu@mediatek.com> wrote:
Hi Walter,
> If the depot_index = STACK_ALLOC_MAX_SLABS - 2 and next_slab_inited = 0,
> then it will cause array out-of-bounds access, so that we should modify
> the detection to avoid this array out-of-bounds bug.
>
> Assume depot_index = STACK_ALLOC_MAX_SLABS - 3
> Consider following call flow sequence:
>
> stack_depot_save()
> depot_alloc_stack()
> if (unlikely(depot_index + 1 >= STACK_ALLOC_MAX_SLABS)) //pass
> depot_index++ //depot_index = STACK_ALLOC_MAX_SLABS - 2
> if (depot_index + 1 < STACK_ALLOC_MAX_SLABS) //enter
> smp_store_release(&next_slab_inited, 0); //next_slab_inited = 0
> init_stack_slab()
> if (stack_slabs[depot_index] == NULL) //enter and exit
>
> stack_depot_save()
> depot_alloc_stack()
> if (unlikely(depot_index + 1 >= STACK_ALLOC_MAX_SLABS)) //pass
> depot_index++ //depot_index = STACK_ALLOC_MAX_SLABS - 1
> init_stack_slab(&prealloc)
> stack_slabs[depot_index + 1] //here get global out-of-bounds
>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: Matthias Brugger <matthias.bgg@gmail.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Alexander Potapenko <glider@google.com>
> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> Cc: Kate Stewart <kstewart@linuxfoundation.org>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Kate Stewart <kstewart@linuxfoundation.org>
> Signed-off-by: Walter Wu <walter-zh.wu@mediatek.com>
> ---
> changes in v2:
> modify call flow sequence and preconditon
>
> changes in v3:
> add some reviewers
> ---
> lib/stackdepot.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index ed717dd08ff3..7e8a15e41600 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -106,7 +106,7 @@ static struct stack_record *depot_alloc_stack(unsigned long *entries, int size,
> required_size = ALIGN(required_size, 1 << STACK_ALLOC_ALIGN);
>
> if (unlikely(depot_offset + required_size > STACK_ALLOC_SIZE)) {
> - if (unlikely(depot_index + 1 >= STACK_ALLOC_MAX_SLABS)) {
> + if (unlikely(depot_index + 2 >= STACK_ALLOC_MAX_SLABS)) {
I don't think this is the right way to fix the problem.
You're basically throwing away the last element of stack_slabs[], as
we won't allocate anything from it.
How about we set |next_slab_inited| to 1 here:
diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 2e7d2232ed3c..943a51eb746d 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -105,6 +105,8 @@ static bool init_stack_slab(void **prealloc)
return true;
if (stack_slabs[depot_index] == NULL) {
stack_slabs[depot_index] = *prealloc;
+ if (depot_index + 1 == STACK_ALLOC_MAX_SLABS)
+ smp_store_release(&next_slab_inited, 1);
} else {
stack_slabs[depot_index + 1] = *prealloc;
/*
This will ensure we won't be preallocating pages once |depot_index|
reaches the last element, and we won't attempt to write those pages
anywhere either.
Could you please check if this fixes the problem for you?
> WARN_ONCE(1, "Stack depot reached limit capacity");
> return NULL;
> }
> --
> 2.18.0
--
Alexander Potapenko
Software Engineer
Google Germany GmbH
Erika-Mann-Straße, 33
80636 München
Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
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next prev parent reply other threads:[~2020-01-30 12:04 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-30 6:44 [PATCH v3] lib/stackdepot: Fix global out-of-bounds in stackdepot Walter Wu
2020-01-30 12:03 ` Alexander Potapenko [this message]
2020-01-31 2:05 ` Walter Wu
2020-01-31 18:11 ` Alexander Potapenko
2020-02-03 2:05 ` Walter Wu
2020-02-03 10:30 ` Alexander Potapenko
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