kasan: always taint kernel on report

Currently we already taint the kernel in some cases.  E.g.  if we hit some
bug in slub memory we call object_err() which will taint the kernel with
TAINT_BAD_PAGE flag.  But for other kind of bugs kernel left untainted.

Always taint with TAINT_BAD_PAGE if kasan found some bug.  This is useful
for automated testing.
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/kasan/report.c

@@ -238,6 +238,7 @@ static void kasan_report_error(struct kasan_access_info *info)
 	}
 	pr_err("================================="
 		"=================================\n");
+	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 	spin_unlock_irqrestore(&report_lock, flags);
 	kasan_enable_current();
 }