Messages in this thread | | | From | Alexander Potapenko <> | Date | Mon, 3 Feb 2020 11:30:28 +0100 | Subject | Re: [PATCH v3] lib/stackdepot: Fix global out-of-bounds in stackdepot |
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On Mon, Feb 3, 2020 at 3:05 AM Walter Wu <walter-zh.wu@mediatek.com> wrote: > > 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?
I've sent the patch. Thanks for the report!
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