[PATCH v3 6/9] kasan: improve slab object description

From: Andrey Konovalov
Date: Mon Mar 06 2017 - 11:02:15 EST


Changes slab object description from:

Object at ffff880068388540, in cache kmalloc-128 size: 128

to:

Object at ffff880068388540 belongs to cache kmalloc-128 of size 128
Access 123 bytes inside of 128-byte region [ffff880068388540, ffff8800683885c0)

This adds information about relative offset of the accessed address to
the start of the object.

Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
---
mm/kasan/report.c | 51 ++++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 40 insertions(+), 11 deletions(-)

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 156f998199e2..87f8293d7b79 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -194,18 +194,47 @@ static struct page *addr_to_page(const void *addr)
return NULL;
}

-static void describe_object(struct kmem_cache *cache, void *object)
+static void describe_object_addr(struct kmem_cache *cache, void *object,
+ const void *addr)
{
- struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
+ unsigned long access_addr = (unsigned long)addr;
+ unsigned long object_addr = (unsigned long)object;
+ const char *rel_type;
+ int rel_bytes;

- pr_err("Object at %p, in cache %s size: %d\n", object, cache->name,
- cache->object_size);
+ pr_err("Object at %p belongs to cache %s of size %d\n",
+ object, cache->name, cache->object_size);

- if (!(cache->flags & SLAB_KASAN))
+ if (!addr)
return;

- print_track(&alloc_info->alloc_track, "Allocated");
- print_track(&alloc_info->free_track, "Freed");
+ if (access_addr < object_addr) {
+ rel_type = "to the left";
+ rel_bytes = object_addr - access_addr;
+ } else if (access_addr >= object_addr + cache->object_size) {
+ rel_type = "to the right";
+ rel_bytes = access_addr - (object_addr + cache->object_size);
+ } else {
+ rel_type = "inside";
+ rel_bytes = access_addr - object_addr;
+ }
+
+ pr_err("Access %d bytes %s of %d-byte region [%p, %p)\n",
+ rel_bytes, rel_type, cache->object_size, (void *)object_addr,
+ (void *)(object_addr + cache->object_size));
+}
+
+static void describe_object(struct kmem_cache *cache, void *object,
+ const void *addr)
+{
+ struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
+
+ if (cache->flags & SLAB_KASAN) {
+ print_track(&alloc_info->alloc_track, "Allocated");
+ print_track(&alloc_info->free_track, "Freed");
+ }
+
+ describe_object_addr(cache, object, addr);
}

void kasan_report_double_free(struct kmem_cache *cache, void *object,
@@ -217,13 +246,13 @@ void kasan_report_double_free(struct kmem_cache *cache, void *object,
pr_err("BUG: Double free or freeing an invalid pointer\n");
pr_err("Unexpected shadow byte: 0x%hhX\n", shadow);
dump_stack();
- describe_object(cache, object);
+ describe_object(cache, object, NULL);
kasan_end_report(&flags);
}

static void print_address_description(struct kasan_access_info *info)
{
- const void *addr = info->access_addr;
+ void *addr = (void *)info->access_addr;
struct page *page = addr_to_page(addr);

if (page)
@@ -233,9 +262,9 @@ static void print_address_description(struct kasan_access_info *info)

if (page && PageSlab(page)) {
struct kmem_cache *cache = page->slab_cache;
- void *object = nearest_obj(cache, page, (void *)addr);
+ void *object = nearest_obj(cache, page, addr);

- describe_object(cache, object);
+ describe_object(cache, object, addr);
}

if (kernel_or_module_addr(addr)) {
--
2.12.0.rc1.440.g5b76565f74-goog