[PATCH 6/6] kasan: improve double-free reports.

Andrey Ryabinin
2016-08-01T16:19:44Z

Currently we just dump stack in case of double free bug.
Let's dump all info about the object that we have.

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
---
mm/kasan/kasan.c | 3 +--
mm/kasan/kasan.h | 2 ++
mm/kasan/report.c | 54 ++++++++++++++++++++++++++++++++++++++----------------
3 files changed, 41 insertions(+), 18 deletions(-)

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index 92750e3..88af13c 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -543,8 +543,7 @@ bool kasan_slab_free(struct kmem_cache *cache, void *object)

shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object));
if (shadow_byte < 0 || shadow_byte >= KASAN_SHADOW_SCALE_SIZE) {
- pr_err("Double free");
- dump_stack();
+ kasan_report_double_free(cache, object, shadow_byte);
return true;
}

diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 9b7b31e..e5c2181 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -99,6 +99,8 @@ static inline bool kasan_report_enabled(void)

void kasan_report(unsigned long addr, size_t size,
bool is_write, unsigned long ip);
+void kasan_report_double_free(struct kmem_cache *cache, void *object,
+ s8 shadow);

#if defined(CONFIG_SLAB) || defined(CONFIG_SLUB)
void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache);
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index f437398..ee2bdb4 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -116,6 +116,26 @@ static inline bool init_task_stack_addr(const void *addr)
sizeof(init_thread_union.stack));
}

+static DEFINE_SPINLOCK(report_lock);
+
+static void kasan_start_report(unsigned long *flags)
+{
+ /*
+ * Make sure we don't end up in loop.
+ */
+ kasan_disable_current();
+ spin_lock_irqsave(&report_lock, *flags);
+ pr_err("==================================================================\n");
+}
+
+static void kasan_end_report(unsigned long *flags)
+{
+ pr_err("==================================================================\n");
+ add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
+ spin_unlock_irqrestore(&report_lock, *flags);
+ kasan_enable_current();
+}
+
static void print_track(struct kasan_track *track)
{
pr_err("PID = %u\n", track->pid);
@@ -129,8 +149,7 @@ static void print_track(struct kasan_track *track)
}
}

-static void kasan_object_err(struct kmem_cache *cache, struct page *page,
- void *object, char *unused_reason)
+static void kasan_object_err(struct kmem_cache *cache, void *object)
{
struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);

@@ -147,6 +166,18 @@ static void kasan_object_err(struct kmem_cache *cache, struct page *page,
print_track(&alloc_info->free_track);
}

+void kasan_report_double_free(struct kmem_cache *cache, void *object,
+ s8 shadow)
+{
+ unsigned long flags;
+
+ kasan_start_report(&flags);
+ pr_err("BUG: Double free or corrupt pointer\n");
+ pr_err("Unexpected shadow byte: 0x%hhX\n", shadow);
+ kasan_object_err(cache, object);
+ kasan_end_report(&flags);
+}
+
static void print_address_description(struct kasan_access_info *info)
{
const void *addr = info->access_addr;
@@ -160,8 +191,7 @@ 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);
- kasan_object_err(cache, page, object,
- "kasan: bad access detected");
+ kasan_object_err(cache, object);
return;
}
dump_page(page, "kasan: bad access detected");
@@ -226,19 +256,13 @@ static void print_shadow_for_address(const void *addr)
}
}

-static DEFINE_SPINLOCK(report_lock);
-
static void kasan_report_error(struct kasan_access_info *info)
{
unsigned long flags;
const char *bug_type;

- /*
- * Make sure we don't end up in loop.
- */
- kasan_disable_current();
- spin_lock_irqsave(&report_lock, flags);
- pr_err("==================================================================\n");
+ kasan_start_report(&flags);
+
if (info->access_addr <
kasan_shadow_to_mem((void *)KASAN_SHADOW_START)) {
if ((unsigned long)info->access_addr < PAGE_SIZE)
@@ -259,10 +283,8 @@ static void kasan_report_error(struct kasan_access_info *info)
print_address_description(info);
print_shadow_for_address(info->first_bad_addr);
}
- pr_err("==================================================================\n");
- add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
- spin_unlock_irqrestore(&report_lock, flags);
- kasan_enable_current();
+
+ kasan_end_report(&flags);
}

void kasan_report(unsigned long addr, size_t size,
--
2.7.3