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Date: Mon, 9 May 2016 13:26:05 +0300
From: Andrey Ryabinin <aryabinin@...tuozzo.com>
To: Kuthonuzo Luruo <kuthonuzo.luruo@....com>, <glider@...gle.com>,
<dvyukov@...gle.com>, <cl@...ux.com>, <penberg@...nel.org>,
<rientjes@...gle.com>, <iamjoonsoo.kim@....com>,
<akpm@...ux-foundation.org>
CC: <kasan-dev@...glegroups.com>, <linux-kernel@...r.kernel.org>,
<linux-mm@...ck.org>
Subject: Re: [PATCH v2 1/2] mm, kasan: improve double-free detection
On 05/06/2016 02:47 PM, Kuthonuzo Luruo wrote:
> Currently, KASAN may fail to detect concurrent deallocations of the same
> object due to a race in kasan_slab_free(). This patch makes double-free
> detection more reliable by serializing access to KASAN object metadata.
> New functions kasan_meta_lock() and kasan_meta_unlock() are provided to
> lock/unlock per-object metadata. Double-free errors are now reported via
> kasan_report().
>
> Testing:
> - Tested with a modified version of the 'slab_test' microbenchmark where
> allocs occur on CPU 0; then all other CPUs concurrently attempt to free
> the same object.
> - Tested with new 'test_kasan' kasan_double_free() test in accompanying
> patch.
>
> Signed-off-by: Kuthonuzo Luruo <kuthonuzo.luruo@....com>
> ---
>
> Changes in v2:
> - Incorporated suggestions from Dmitry Vyukov. New per-object metadata
> lock/unlock functions; kasan_alloc_meta modified to add new state while
> using fewer bits overall.
> - Double-free pr_err promoted to kasan_report().
> - kasan_init_object() introduced to initialize KASAN object metadata
> during slab creation. KASAN_STATE_INIT initialization removed from
> kasan_poison_object_data().
>
> ---
> include/linux/kasan.h | 8 +++
> mm/kasan/kasan.c | 118 ++++++++++++++++++++++++++++++++++++-------------
> mm/kasan/kasan.h | 15 +++++-
> mm/kasan/quarantine.c | 7 +++-
> mm/kasan/report.c | 31 +++++++++++--
> mm/slab.c | 1 +
> 6 files changed, 142 insertions(+), 38 deletions(-)
>
Sorry, but this patch is crap.
Something like this, will fix the race:
---
mm/kasan/kasan.c | 20 ++++----------------
mm/kasan/kasan.h | 10 +++-------
mm/kasan/quarantine.c | 1 -
mm/kasan/report.c | 11 ++---------
4 files changed, 9 insertions(+), 33 deletions(-)
diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index ef2e87b..8d078dc 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -419,13 +419,6 @@ void kasan_poison_object_data(struct kmem_cache *cache, void *object)
kasan_poison_shadow(object,
round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE),
KASAN_KMALLOC_REDZONE);
-#ifdef CONFIG_SLAB
- if (cache->flags & SLAB_KASAN) {
- struct kasan_alloc_meta *alloc_info =
- get_alloc_info(cache, object);
- alloc_info->state = KASAN_STATE_INIT;
- }
-#endif
}
#ifdef CONFIG_SLAB
@@ -521,20 +514,15 @@ bool kasan_slab_free(struct kmem_cache *cache, void *object)
struct kasan_free_meta *free_info =
get_free_info(cache, object);
- switch (alloc_info->state) {
- case KASAN_STATE_ALLOC:
- alloc_info->state = KASAN_STATE_QUARANTINE;
+ if (test_and_clear_bit(KASAN_STATE_ALLOCATED,
+ &alloc_info->state)) {
quarantine_put(free_info, cache);
set_track(&free_info->track, GFP_NOWAIT);
kasan_poison_slab_free(cache, object);
return true;
- case KASAN_STATE_QUARANTINE:
- case KASAN_STATE_FREE:
+ } else {
pr_err("Double free");
dump_stack();
- break;
- default:
- break;
}
}
return false;
@@ -571,7 +559,7 @@ void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
struct kasan_alloc_meta *alloc_info =
get_alloc_info(cache, object);
- alloc_info->state = KASAN_STATE_ALLOC;
+ set_bit(KASAN_STATE_ALLOCATED, &alloc_info->state);
alloc_info->alloc_size = size;
set_track(&alloc_info->track, flags);
}
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 7da78a6..2dcdc8f 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -60,10 +60,7 @@ struct kasan_global {
*/
enum kasan_state {
- KASAN_STATE_INIT,
- KASAN_STATE_ALLOC,
- KASAN_STATE_QUARANTINE,
- KASAN_STATE_FREE
+ KASAN_STATE_ALLOCATED,
};
#define KASAN_STACK_DEPTH 64
@@ -75,9 +72,8 @@ struct kasan_track {
struct kasan_alloc_meta {
struct kasan_track track;
- u32 state : 2; /* enum kasan_state */
- u32 alloc_size : 30;
- u32 reserved;
+ unsigned long state;
+ u32 alloc_size;
};
struct kasan_free_meta {
diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
index 40159a6..ca33fd3 100644
--- a/mm/kasan/quarantine.c
+++ b/mm/kasan/quarantine.c
@@ -147,7 +147,6 @@ static void qlink_free(void **qlink, struct kmem_cache *cache)
unsigned long flags;
local_irq_save(flags);
- alloc_info->state = KASAN_STATE_FREE;
___cache_free(cache, object, _THIS_IP_);
local_irq_restore(flags);
}
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index b3c122d..c2b0e51 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -140,18 +140,12 @@ static void object_err(struct kmem_cache *cache, struct page *page,
pr_err("Object at %p, in cache %s\n", object, cache->name);
if (!(cache->flags & SLAB_KASAN))
return;
- switch (alloc_info->state) {
- case KASAN_STATE_INIT:
- pr_err("Object not allocated yet\n");
- break;
- case KASAN_STATE_ALLOC:
+ if (test_bit(KASAN_STATE_ALLOCATED, &alloc_info->state)) {
pr_err("Object allocated with size %u bytes.\n",
alloc_info->alloc_size);
pr_err("Allocation:\n");
print_track(&alloc_info->track);
- break;
- case KASAN_STATE_FREE:
- case KASAN_STATE_QUARANTINE:
+ } else {
pr_err("Object freed, allocated with size %u bytes\n",
alloc_info->alloc_size);
free_info = get_free_info(cache, object);
@@ -159,7 +153,6 @@ static void object_err(struct kmem_cache *cache, struct page *page,
print_track(&alloc_info->track);
pr_err("Deallocation:\n");
print_track(&free_info->track);
- break;
}
}
#endif
--
2.7.3
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