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.lu...@hpe.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(-)
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 645c280..c7bf625 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -78,6 +78,10 @@ struct kasan_cache {
int kasan_module_alloc(void *addr, size_t size);
void kasan_free_shadow(const struct vm_struct *vm);
+#ifdef CONFIG_SLAB
+void kasan_init_object(struct kmem_cache *cache, void *object);
+#endif
+
#else /* CONFIG_KASAN */
static inline void kasan_unpoison_shadow(const void *address, size_t size) {}
@@ -124,6 +128,10 @@ static inline void kasan_poison_slab_free(struct
kmem_cache *s, void *object) {}
static inline int kasan_module_alloc(void *addr, size_t size) { return 0; }
static inline void kasan_free_shadow(const struct vm_struct *vm) {}
+#ifdef CONFIG_SLAB
+static inline void kasan_init_object(struct kmem_cache *cache, void *object) {}
+#endif
+
#endif /* CONFIG_KASAN */
#endif /* LINUX_KASAN_H */
diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index ef2e87b..a840b49 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -34,6 +34,7 @@
#include <linux/string.h>
#include <linux/types.h>
#include <linux/vmalloc.h>
+#include <linux/atomic.h>
#include "kasan.h"
#include "../slab.h"
@@ -419,13 +420,6 @@ 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
@@ -470,6 +464,18 @@ static inline depot_stack_handle_t save_stack(gfp_t flags)
return depot_save_stack(&trace, flags);
}
+void kasan_init_object(struct kmem_cache *cache, void *object)
+{
+ struct kasan_alloc_meta *alloc_info;
+
+ if (cache->flags & SLAB_KASAN) {
+ kasan_unpoison_object_data(cache, object);
+ alloc_info = get_alloc_info(cache, object);
+ __memset(alloc_info, 0, sizeof(*alloc_info));
+ kasan_poison_object_data(cache, object);
+ }
+}
+
static inline void set_track(struct kasan_track *track, gfp_t flags)
{
track->pid = current->pid;
@@ -489,6 +495,39 @@ struct kasan_free_meta *get_free_info(struct kmem_cache
*cache,
BUILD_BUG_ON(sizeof(struct kasan_free_meta) > 32);
return (void *)object + cache->kasan_info.free_meta_offset;
}
+
+/* acquire per-object lock for access to KASAN metadata. */
+void kasan_meta_lock(struct kasan_alloc_meta *alloc_info)
+{
+ union kasan_alloc_data old, new;
+
+ preempt_disable();
+ for (;;) {
+ old.packed = READ_ONCE(alloc_info->data);
+ if (unlikely(old.lock)) {
+ cpu_relax();
+ continue;
+ }
+ new.packed = old.packed;
+ new.lock = 1;
+ if (likely(cmpxchg(&alloc_info->data, old.packed, new.packed)
+ == old.packed))
+ break;
+ }
+}
+
+/* release lock after a kasan_meta_lock(). */
+void kasan_meta_unlock(struct kasan_alloc_meta *alloc_info)
+{
+ union kasan_alloc_data alloc_data;
+
+ alloc_data.packed = READ_ONCE(alloc_info->data);
+ alloc_data.lock = 0;
+ if (unlikely(xchg(&alloc_info->data, alloc_data.packed) !=
+ (alloc_data.packed | 0x1U)))
+ WARN_ONCE(1, "%s: lock not held!\n", __func__);
+ preempt_enable();
+}
#endif
void kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags)
@@ -511,32 +550,41 @@ void kasan_poison_slab_free(struct kmem_cache *cache,
void *object)
bool kasan_slab_free(struct kmem_cache *cache, void *object)
{
#ifdef CONFIG_SLAB
+ struct kasan_alloc_meta *alloc_info;
+ struct kasan_free_meta *free_info;
+ union kasan_alloc_data alloc_data;
+
/* RCU slabs could be legally used after free within the RCU period */
if (unlikely(cache->flags & SLAB_DESTROY_BY_RCU))
return false;
- if (likely(cache->flags & SLAB_KASAN)) {
- struct kasan_alloc_meta *alloc_info =
- get_alloc_info(cache, 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;
- 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:
- pr_err("Double free");
- dump_stack();
- break;
- default:
- break;
- }
+ if (unlikely(!(cache->flags & SLAB_KASAN)))
+ return false;
+
+ alloc_info = get_alloc_info(cache, object);
+ kasan_meta_lock(alloc_info);
+ alloc_data.packed = alloc_info->data;
+ if (alloc_data.state == KASAN_STATE_ALLOC) {
+ free_info = get_free_info(cache, object);
+ quarantine_put(free_info, cache);
+ set_track(&free_info->track, GFP_NOWAIT);
+ kasan_poison_slab_free(cache, object);
+ alloc_data.state = KASAN_STATE_QUARANTINE;
+ alloc_info->data = alloc_data.packed;
+ kasan_meta_unlock(alloc_info);
+ return true;
}
+ switch (alloc_data.state) {
+ case KASAN_STATE_QUARANTINE:
+ case KASAN_STATE_FREE:
+ kasan_report((unsigned long)object, 0, false,
+ (unsigned long)__builtin_return_address(1));
+ kasan_meta_unlock(alloc_info);
+ return true;
+ default:
+ break;
+ }
+ kasan_meta_unlock(alloc_info);
return false;
#else
kasan_poison_slab_free(cache, object);
@@ -568,12 +616,20 @@ void kasan_kmalloc(struct kmem_cache *cache, const void
*object, size_t size,
KASAN_KMALLOC_REDZONE);
#ifdef CONFIG_SLAB
if (cache->flags & SLAB_KASAN) {
+ union kasan_alloc_data alloc_data;
struct kasan_alloc_meta *alloc_info =
get_alloc_info(cache, object);
-
- alloc_info->state = KASAN_STATE_ALLOC;
- alloc_info->alloc_size = size;
+ unsigned long flags;
+
+ local_irq_save(flags);
+ kasan_meta_lock(alloc_info);
+ alloc_data.packed = alloc_info->data;
+ alloc_data.state = KASAN_STATE_ALLOC;
+ alloc_data.size_delta = cache->object_size - size;
+ alloc_info->data = alloc_data.packed;
set_track(&alloc_info->track, flags);
+ kasan_meta_unlock(alloc_info);
+ local_irq_restore(flags);
}
#endif
}
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 7da78a6..df2724d 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -73,10 +73,19 @@ struct kasan_track {
depot_stack_handle_t stack;
};
+union kasan_alloc_data {
+ struct {
+ u32 lock : 1;
+ u32 state : 2; /* enum kasan_state */
+ u32 size_delta : 24; /* object_size - alloc size */
+ u32 unused : 5;
+ };
+ u32 packed;
+};
+
struct kasan_alloc_meta {
struct kasan_track track;
- u32 state : 2; /* enum kasan_state */
- u32 alloc_size : 30;
+ u32 data; /* encoded as union kasan_alloc_data */
u32 reserved;
};
@@ -112,4 +121,6 @@ void quarantine_put(struct kasan_free_meta *info, struct
kmem_cache *cache);
void quarantine_reduce(void);
void quarantine_remove_cache(struct kmem_cache *cache);
+void kasan_meta_lock(struct kasan_alloc_meta *alloc_info);
+void kasan_meta_unlock(struct kasan_alloc_meta *alloc_info);
#endif
diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
index 40159a6..d59a569 100644
--- a/mm/kasan/quarantine.c
+++ b/mm/kasan/quarantine.c
@@ -144,10 +144,15 @@ static void qlink_free(void **qlink, struct kmem_cache
*cache)
{
void *object = qlink_to_object(qlink, cache);
struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
+ union kasan_alloc_data alloc_data;
unsigned long flags;
local_irq_save(flags);
- alloc_info->state = KASAN_STATE_FREE;
+ kasan_meta_lock(alloc_info);
+ alloc_data.packed = alloc_info->data;
+ alloc_data.state = KASAN_STATE_FREE;
+ alloc_info->data = alloc_data.packed;
+ kasan_meta_unlock(alloc_info);
___cache_free(cache, object, _THIS_IP_);
local_irq_restore(flags);
}
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index b3c122d..cecf2fa 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -53,6 +53,17 @@ static void print_error_description(struct kasan_access_info
*info)
const char *bug_type = "unknown-crash";
u8 *shadow_addr;
+#ifdef CONFIG_SLAB
+ if (!info->access_size) {
+ pr_err("BUG: KASAN: double-free attempt in %pS on object at
addr %p\n",
+ (void *)info->ip, info->access_addr);
+ pr_err("Double free by task %s/%d\n",
+ current->comm, task_pid_nr(current));
+ info->first_bad_addr = info->access_addr;
+ return;
+ }
+#endif
+
info->first_bad_addr = find_first_bad_addr(info->access_addr,
info->access_size);
@@ -131,29 +142,34 @@ static void print_track(struct kasan_track *track)
}
static void object_err(struct kmem_cache *cache, struct page *page,
- void *object, char *unused_reason)
+ void *object, char *unused_reason,
+ struct kasan_access_info *info)
{
struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
struct kasan_free_meta *free_info;
+ union kasan_alloc_data alloc_data;
dump_stack();
pr_err("Object at %p, in cache %s\n", object, cache->name);
if (!(cache->flags & SLAB_KASAN))
return;
- switch (alloc_info->state) {
+ if (info->access_size)
+ kasan_meta_lock(alloc_info);
+ alloc_data.packed = alloc_info->data;
+ switch (alloc_data.state) {
case KASAN_STATE_INIT:
pr_err("Object not allocated yet\n");
break;
case KASAN_STATE_ALLOC:
pr_err("Object allocated with size %u bytes.\n",
- alloc_info->alloc_size);
+ (cache->object_size - alloc_data.size_delta));
pr_err("Allocation:\n");
print_track(&alloc_info->track);
break;
case KASAN_STATE_FREE:
case KASAN_STATE_QUARANTINE:
pr_err("Object freed, allocated with size %u bytes\n",
- alloc_info->alloc_size);
+ (cache->object_size - alloc_data.size_delta));
free_info = get_free_info(cache, object);
pr_err("Allocation:\n");
print_track(&alloc_info->track);
@@ -161,6 +177,8 @@ static void object_err(struct kmem_cache *cache, struct
page *page,
print_track(&free_info->track);
break;
}
+ if (info->access_size)
+ kasan_meta_unlock(alloc_info);
}
#endif
@@ -177,8 +195,13 @@ static void print_address_description(struct
kasan_access_info *info)
struct kmem_cache *cache = page->slab_cache;
object = nearest_obj(cache, page,
(void *)info->access_addr);
+#ifdef CONFIG_SLAB
+ object_err(cache, page, object,
+ "kasan: bad access detected", info);
+#else
object_err(cache, page, object,
"kasan: bad access detected");
+#endif
return;
}
dump_page(page, "kasan: bad access detected");
diff --git a/mm/slab.c b/mm/slab.c
index 3f20800..110d586 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2651,6 +2651,7 @@ static void cache_init_objs(struct kmem_cache *cachep,
cachep->ctor(objp);
kasan_poison_object_data(cachep, objp);
}
+ kasan_init_object(cachep, index_to_obj(cachep, page, i));
if (!shuffled)
set_free_obj(page, i, i);
--
1.7.1
