lkdtm: Add FAM_BOUNDS test for __counted_by

Add new CONFIG_UBSAN_BOUNDS test for __counted_by attribute.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kees Cook <keescook@chromium.org>

drivers/misc/lkdtm/bugs.c

@@ -273,8 +273,8 @@ static void lkdtm_HUNG_TASK(void)
 	schedule();
 }
 
-volatile unsigned int huge = INT_MAX - 2;
-volatile unsigned int ignored;
+static volatile unsigned int huge = INT_MAX - 2;
+static volatile unsigned int ignored;
 
 static void lkdtm_OVERFLOW_SIGNED(void)
 {
@@ -305,7 +305,7 @@ static void lkdtm_OVERFLOW_UNSIGNED(void)
 	ignored = value;
 }
 
-/* Intentionally using old-style flex array definition of 1 byte. */
+/* Intentionally using unannotated flex array definition. */
 struct array_bounds_flex_array {
 	int one;
 	int two;
@@ -357,6 +357,46 @@ static void lkdtm_ARRAY_BOUNDS(void)
 		pr_expected_config(CONFIG_UBSAN_BOUNDS);
 }
 
+struct lkdtm_annotated {
+	unsigned long flags;
+	int count;
+	int array[] __counted_by(count);
+};
+
+static volatile int fam_count = 4;
+
+static void lkdtm_FAM_BOUNDS(void)
+{
+	struct lkdtm_annotated *inst;
+
+	inst = kzalloc(struct_size(inst, array, fam_count + 1), GFP_KERNEL);
+	if (!inst) {
+		pr_err("FAIL: could not allocate test struct!\n");
+		return;
+	}
+
+	inst->count = fam_count;
+	pr_info("Array access within bounds ...\n");
+	inst->array[1] = fam_count;
+	ignored = inst->array[1];
+
+	pr_info("Array access beyond bounds ...\n");
+	inst->array[fam_count] = fam_count;
+	ignored = inst->array[fam_count];
+
+	kfree(inst);
+
+	pr_err("FAIL: survived access of invalid flexible array member index!\n");
+
+	if (!__has_attribute(__counted_by__))
+		pr_warn("This is expected since this %s was built a compiler supporting __counted_by\n",
+			lkdtm_kernel_info);
+	else if (IS_ENABLED(CONFIG_UBSAN_BOUNDS))
+		pr_expected_config(CONFIG_UBSAN_TRAP);
+	else
+		pr_expected_config(CONFIG_UBSAN_BOUNDS);
+}
+
 static void lkdtm_CORRUPT_LIST_ADD(void)
 {
 	/*
@@ -616,6 +656,7 @@ static struct crashtype crashtypes[] = {
 	CRASHTYPE(OVERFLOW_SIGNED),
 	CRASHTYPE(OVERFLOW_UNSIGNED),
 	CRASHTYPE(ARRAY_BOUNDS),
+	CRASHTYPE(FAM_BOUNDS),
 	CRASHTYPE(CORRUPT_LIST_ADD),
 	CRASHTYPE(CORRUPT_LIST_DEL),
 	CRASHTYPE(STACK_GUARD_PAGE_LEADING),