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

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Message-ID: <20200130064430.17198-1-walter-zh.wu@mediatek.com>
Date:   Thu, 30 Jan 2020 14:44:30 +0800
From:   Walter Wu <walter-zh.wu@...iatek.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexander Potapenko <glider@...gle.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kate Stewart <kstewart@...uxfoundation.org>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>,
        wsd_upstream <wsd_upstream@...iatek.com>,
        Walter Wu <walter-zh.wu@...iatek.com>
Subject: [PATCH v3] lib/stackdepot: Fix global out-of-bounds in stackdepot

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@...gle.com>
Cc: Matthias Brugger <matthias.bgg@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Alexander Potapenko <glider@...gle.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Kate Stewart <kstewart@...uxfoundation.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Kate Stewart <kstewart@...uxfoundation.org>
Signed-off-by: Walter Wu <walter-zh.wu@...iatek.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