Messages in this thread Patch in this message | | | Subject | Re: [PATCH v3] lib/stackdepot: Fix global out-of-bounds in stackdepot | From | Walter Wu <> | Date | Fri, 31 Jan 2020 10:05:06 +0800 |
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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)) { > > 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. > ok, I agree.
> 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? > Consider above call flow sequence at first stack_depot_save(), depot_index = STACK_ALLOC_MAX_SLABS - 2 before enter init_stack_slab(), so the fixes should be below.
--- a/lib/stackdepot.c +++ b/lib/stackdepot.c @@ -83,6 +83,8 @@ static bool init_stack_slab(void **prealloc) return true; if (stack_slabs[depot_index] == NULL) { stack_slabs[depot_index] = *prealloc; + if (depot_index + 2 == STACK_ALLOC_MAX_SLABS) + smp_store_release(&next_slab_inited, 1); } else { stack_slabs[depot_index + 1] = *prealloc; /*
> > WARN_ONCE(1, "Stack depot reached limit capacity"); > > return NULL; > > } > > -- > > 2.18.0 > > >
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