kasan: improve double-free report format

Changes double-free report header from

  BUG: Double free or freeing an invalid pointer
  Unexpected shadow byte: 0xFB

to

  BUG: KASAN: double-free or invalid-free in kmalloc_oob_left+0xe5/0xef

This makes a bug uniquely identifiable by the first report line.  To
account for removing of the unexpected shadow value, print shadow bytes
at the end of the report as in reports for other kinds of bugs.

Link: http://lkml.kernel.org/r/20170302134851.101218-9-andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/kasan/kasan.h

@@ -99,7 +99,7 @@ static inline const void *kasan_shadow_to_mem(const void *shadow_addr)
 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);
+					void *ip);
 
 #if defined(CONFIG_SLAB) || defined(CONFIG_SLUB)
 void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache);