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Subject[PATCH v3] lib/stackdepot: Fix global out-of-bounds in stackdepot
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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
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