From: Walter Wu <walter-zh.wu@mediatek.com>
To: Alexander Potapenko <glider@google.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: Mon, 3 Feb 2020 10:05:44 +0800 [thread overview]
Message-ID: <1580695544.17006.7.camel@mtksdccf07> (raw)
In-Reply-To: <CAG_fn=X2V0nL=+s38bDbS3UXf2_i61tSevd8vzkV-ZKY=7MHvw@mail.gmail.com>
On Fri, 2020-01-31 at 19:11 +0100, Alexander Potapenko wrote:
> On Fri, Jan 31, 2020 at 3:05 AM Walter Wu <walter-zh.wu@mediatek.com> wrote:
> >
> > On Thu, 2020-01-30 at 13:03 +0100, Alexander Potapenko wrote:
> > > 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)) {
>
> This again means stack_slabs[STACK_ALLOC_MAX_SLABS - 2] gets
> initialized, but stack_slabs[STACK_ALLOC_MAX_SLABS - 1] doesn't,
> because we'll be bailing out from init_stack_slab() from now on.
> Does this patch actually fix the problem (do you have a reliable reproducer?)
We get it by reviewing code, because Kasan doesn't scan it and we catch
another bug internally, we found it unintentionally.
> This addition of 2 is also counterintuitive, I don't think further
> readers will understand the logic behind it.
>
Yes
> What if we just check that depot_index + 1 is a valid index before accessing it?
>
It should fix the problem, do you want to send this patch?
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index 2e7d2232ed3c..c2e6ff18d716 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -106,7 +106,9 @@ static bool init_stack_slab(void **prealloc)
> if (stack_slabs[depot_index] == NULL) {
> stack_slabs[depot_index] = *prealloc;
> } else {
> - stack_slabs[depot_index + 1] = *prealloc;
> + /* If this is the last depot slab, do not touch the next one. */
> + if (depot_index + 1 < STACK_ALLOC_MAX_SLABS)
> + stack_slabs[depot_index + 1] = *prealloc;
> /*
> * This smp_store_release pairs with smp_load_acquire() from
> * |next_slab_inited| above and in stack_depot_save().
_______________________________________________
Linux-mediatek mailing list
Linux-mediatek@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-mediatek
next prev parent reply other threads:[~2020-02-03 2:06 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
2020-01-31 2:05 ` Walter Wu
2020-01-31 18:11 ` Alexander Potapenko
2020-02-03 2:05 ` Walter Wu [this message]
2020-02-03 10:30 ` Alexander Potapenko
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1580695544.17006.7.camel@mtksdccf07 \
--to=walter-zh.wu@mediatek.com \
--cc=dvyukov@google.com \
--cc=glider@google.com \
--cc=gregkh@linuxfoundation.org \
--cc=jpoimboe@redhat.com \
--cc=kstewart@linuxfoundation.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mediatek@lists.infradead.org \
--cc=matthias.bgg@gmail.com \
--cc=tglx@linutronix.de \
--cc=wsd_upstream@mediatek.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).