[PATCH v2] kunit: run test suites only after module initialization completes

[Marco Pagani]

Commit 2810c1e99867 ("kunit: Fix wild-memory-access bug in
kunit_free_suite_set()") fixed a wild-memory-access bug that could have
happened during the loading phase of test suites built and executed as
loadable modules. However, it also introduced a problematic side effect
that causes test suites modules to crash when they attempt to register
fake devices.

When a module is loaded, it traverses the MODULE_STATE_UNFORMED and
MODULE_STATE_COMING states before reaching the normal operating state
MODULE_STATE_LIVE. Finally, when the module is removed, it moves to
MODULE_STATE_GOING before being released. However, if the loading
function load_module() fails between complete_formation() and
do_init_module(), the module goes directly from MODULE_STATE_COMING to
MODULE_STATE_GOING without passing through MODULE_STATE_LIVE.

This behavior was causing kunit_module_exit() to be called without
having first executed kunit_module_init(). Since kunit_module_exit() is
responsible for freeing the memory allocated by kunit_module_init()
through kunit_filter_suites(), this behavior was resulting in a
wild-memory-access bug.

Commit 2810c1e99867 ("kunit: Fix wild-memory-access bug in
kunit_free_suite_set()") fixed this issue by running the tests when the
module is still in MODULE_STATE_COMING. However, modules in that state
are not fully initialized, lacking sysfs kobjects. Therefore, if a test
module attempts to register a fake device, it will inevitably crash.

This patch proposes a different approach to fix the original
wild-memory-access bug while restoring the normal module execution flow
by making kunit_module_exit() able to detect if kunit_module_init() has
previously initialized the tests suite set. In this way, test modules
can once again register fake devices without crashing.

This behavior is achieved by checking whether mod->kunit_suites is a
virtual or direct mapping address. If it is a virtual address, then
kunit_module_init() has allocated the suite_set in kunit_filter_suites()
using kmalloc_array(). On the contrary, if mod->kunit_suites is still
pointing to the original address that was set when looking up the
.kunit_test_suites section of the module, then the loading phase has
failed and there's no memory to be freed.

v2:
- add include <linux/mm.h>

Fixes: 2810c1e99867 ("kunit: Fix wild-memory-access bug in kunit_free_suite_set()")
Signed-off-by: Marco Pagani <marpagan@xxxxxxxxxx>
---
 lib/kunit/test.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/lib/kunit/test.c b/lib/kunit/test.c
index f2eb71f1a66c..0e829b9f8ce5 100644
--- a/lib/kunit/test.c
+++ b/lib/kunit/test.c
@@ -16,6 +16,7 @@
 #include <linux/panic.h>
 #include <linux/sched/debug.h>
 #include <linux/sched.h>
+#include <linux/mm.h>
 
 #include "debugfs.h"
 #include "hooks-impl.h"
@@ -737,12 +738,14 @@ static void kunit_module_exit(struct module *mod)
 	};
 	const char *action = kunit_action();
 
+	if (!suite_set.start || !virt_addr_valid(suite_set.start))
+		return;
+
 	if (!action)
 		__kunit_test_suites_exit(mod->kunit_suites,
 					 mod->num_kunit_suites);
 
-	if (suite_set.start)
-		kunit_free_suite_set(suite_set);
+	kunit_free_suite_set(suite_set);
 }
 
 static int kunit_module_notify(struct notifier_block *nb, unsigned long val,
@@ -752,12 +755,12 @@ static int kunit_module_notify(struct notifier_block *nb, unsigned long val,
 
 	switch (val) {
 	case MODULE_STATE_LIVE:
+		kunit_module_init(mod);
 		break;
 	case MODULE_STATE_GOING:
 		kunit_module_exit(mod);
 		break;
 	case MODULE_STATE_COMING:
-		kunit_module_init(mod);
 		break;
 	case MODULE_STATE_UNFORMED:
 		break;

base-commit: 2cc14f52aeb78ce3f29677c2de1f06c0e91471ab
-- 
2.42.0