* [PATCH v3] lib/stackdepot: Fix global out-of-bounds in stackdepot
@ 2020-01-30 6:44 Walter Wu
2020-01-30 12:03 ` Alexander Potapenko
0 siblings, 1 reply; 6+ messages in thread
From: Walter Wu @ 2020-01-30 6:44 UTC (permalink / raw)
To: Dmitry Vyukov, Matthias Brugger, Thomas Gleixner,
Alexander Potapenko, Josh Poimboeuf, Greg Kroah-Hartman,
Kate Stewart
Cc: linux-kernel, linux-arm-kernel, linux-mediatek, wsd_upstream, Walter Wu
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)) {
WARN_ONCE(1, "Stack depot reached limit capacity");
return NULL;
}
--
2.18.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH v3] lib/stackdepot: Fix global out-of-bounds in stackdepot 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 0 siblings, 1 reply; 6+ messages in thread From: Alexander Potapenko @ 2020-01-30 12:03 UTC (permalink / raw) To: Walter Wu Cc: Dmitry Vyukov, Matthias Brugger, Thomas Gleixner, Josh Poimboeuf, Greg Kroah-Hartman, Kate Stewart, LKML, linux-arm-kernel, linux-mediatek, wsd_upstream 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 ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH v3] lib/stackdepot: Fix global out-of-bounds in stackdepot 2020-01-30 12:03 ` Alexander Potapenko @ 2020-01-31 2:05 ` Walter Wu 2020-01-31 18:11 ` Alexander Potapenko 0 siblings, 1 reply; 6+ messages in thread From: Walter Wu @ 2020-01-31 2:05 UTC (permalink / raw) To: Alexander Potapenko Cc: Dmitry Vyukov, Matthias Brugger, Thomas Gleixner, Josh Poimboeuf, Greg Kroah-Hartman, Kate Stewart, LKML, linux-arm-kernel, linux-mediatek, wsd_upstream 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 > > > ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v3] lib/stackdepot: Fix global out-of-bounds in stackdepot 2020-01-31 2:05 ` Walter Wu @ 2020-01-31 18:11 ` Alexander Potapenko 2020-02-03 2:05 ` Walter Wu 0 siblings, 1 reply; 6+ messages in thread From: Alexander Potapenko @ 2020-01-31 18:11 UTC (permalink / raw) To: Walter Wu Cc: Dmitry Vyukov, Matthias Brugger, Thomas Gleixner, Josh Poimboeuf, Greg Kroah-Hartman, Kate Stewart, LKML, linux-arm-kernel, linux-mediatek, wsd_upstream 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?) This addition of 2 is also counterintuitive, I don't think further readers will understand the logic behind it. What if we just check that depot_index + 1 is a valid index before accessing it? 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(). ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH v3] lib/stackdepot: Fix global out-of-bounds in stackdepot 2020-01-31 18:11 ` Alexander Potapenko @ 2020-02-03 2:05 ` Walter Wu 2020-02-03 10:30 ` Alexander Potapenko 0 siblings, 1 reply; 6+ messages in thread From: Walter Wu @ 2020-02-03 2:05 UTC (permalink / raw) To: Alexander Potapenko Cc: Dmitry Vyukov, Matthias Brugger, Thomas Gleixner, Josh Poimboeuf, Greg Kroah-Hartman, Kate Stewart, LKML, linux-arm-kernel, linux-mediatek, wsd_upstream 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(). ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v3] lib/stackdepot: Fix global out-of-bounds in stackdepot 2020-02-03 2:05 ` Walter Wu @ 2020-02-03 10:30 ` Alexander Potapenko 0 siblings, 0 replies; 6+ messages in thread From: Alexander Potapenko @ 2020-02-03 10:30 UTC (permalink / raw) To: Walter Wu Cc: Dmitry Vyukov, Matthias Brugger, Thomas Gleixner, Josh Poimboeuf, Greg Kroah-Hartman, Kate Stewart, LKML, linux-arm-kernel, linux-mediatek, wsd_upstream 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! ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2020-02-03 10:30 UTC | newest] Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 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 2020-02-03 10:30 ` Alexander Potapenko
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