[PATCH] kunit: Device wrappers should also manage driver name

[David Gow <davidgow@google.com>]

kunit_driver_create() accepts a name for the driver, but does not copy
it, so if that name is either on the stack, or otherwise freed, we end
up with a use-after-free when the driver is cleaned up.

Instead, strdup() the name, and manage it as another KUnit allocation.
As there was no existing kunit_kstrdup(), we add one. Further, add a
kunit_ variant of strdup_const() and kfree_const(), so we don't need to
allocate and manage the string in the majority of cases where it's a
constant.

This fixes a KASAN splat with overflow.overflow_allocation_test, when
built as a module.

Fixes: d03c720e03bd ("kunit: Add APIs for managing devices")
Reported-by: Nico Pache <npache@redhat.com>
Closes: https://groups.google.com/g/kunit-dev/c/81V9b9QYON0
Signed-off-by: David Gow <davidgow@google.com>
Reviewed-by: Kees Cook <kees@kernel.org>
---

There's some more serious changes since the RFC I sent, so please take a
closer look.

Thanks,
-- David

Changes since RFC:
https://groups.google.com/g/kunit-dev/c/81V9b9QYON0/m/PFKNKDKAAAAJ
- Add and use the kunit_kstrdup_const() and kunit_free_const()
  functions.
- Fix a typo in the doc comments.


---
 include/kunit/test.h | 58 ++++++++++++++++++++++++++++++++++++++++++++
 lib/kunit/device.c   |  7 ++++--
 2 files changed, 63 insertions(+), 2 deletions(-)

diff --git a/include/kunit/test.h b/include/kunit/test.h
index e2a1f0928e8b..da9e84de14c0 100644
--- a/include/kunit/test.h
+++ b/include/kunit/test.h
@@ -28,6 +28,7 @@
 #include <linux/types.h>
 
 #include <asm/rwonce.h>
+#include <asm/sections.h>
 
 /* Static key: true if any KUnit tests are currently running */
 DECLARE_STATIC_KEY_FALSE(kunit_running);
@@ -480,6 +481,63 @@ static inline void *kunit_kcalloc(struct kunit *test, size_t n, size_t size, gfp
 	return kunit_kmalloc_array(test, n, size, gfp | __GFP_ZERO);
 }
 
+
+/**
+ * kunit_kfree_const() - conditionally free test managed memory
+ * @x: pointer to the memory
+ *
+ * Calls kunit_kfree() only if @x is not in .rodata section.
+ * See kunit_kstrdup_const() for more information.
+ */
+static inline void kunit_kfree_const(struct kunit *test, const void *x)
+{
+	if (!is_kernel_rodata((unsigned long)x))
+		kunit_kfree(test, x);
+}
+
+/**
+ * kunit_kstrdup() - Duplicates a string into a test managed allocation.
+ *
+ * @test: The test context object.
+ * @str: The NULL-terminated string to duplicate.
+ * @gfp: flags passed to underlying kmalloc().
+ *
+ * See kstrdup() and kunit_kmalloc_array() for more information.
+ */
+static inline char *kunit_kstrdup(struct kunit *test, const char *str, gfp_t gfp)
+{
+	size_t len;
+	char *buf;
+
+	if (!str)
+		return NULL;
+
+	len = strlen(str) + 1;
+	buf = kunit_kmalloc(test, len, gfp);
+	if (buf)
+		memcpy(buf, str, len);
+	return buf;
+}
+
+/**
+ * kunit_kstrdup_const() - Conditionally duplicates a string into a test managed allocation.
+ *
+ * @test: The test context object.
+ * @str: The NULL-terminated string to duplicate.
+ * @gfp: flags passed to underlying kmalloc().
+ *
+ * Calls kunit_kstrdup() only if @str is not in the rodata section. Must be freed with
+ * kunit_free_const() -- not kunit_free().
+ * See kstrdup_const() and kunit_kmalloc_array() for more information.
+ */
+static inline const char *kunit_kstrdup_const(struct kunit *test, const char *str, gfp_t gfp)
+{
+	if (is_kernel_rodata((unsigned long)str))
+		return str;
+
+	return kunit_kstrdup(test, str, gfp);
+}
+
 /**
  * kunit_vm_mmap() - Allocate KUnit-tracked vm_mmap() area
  * @test: The test context object.
diff --git a/lib/kunit/device.c b/lib/kunit/device.c
index 25c81ed465fb..520c1fccee8a 100644
--- a/lib/kunit/device.c
+++ b/lib/kunit/device.c
@@ -89,7 +89,7 @@ struct device_driver *kunit_driver_create(struct kunit *test, const char *name)
 	if (!driver)
 		return ERR_PTR(err);
 
-	driver->name = name;
+	driver->name = kunit_kstrdup_const(test, name, GFP_KERNEL);
 	driver->bus = &kunit_bus_type;
 	driver->owner = THIS_MODULE;
 
@@ -192,8 +192,11 @@ void kunit_device_unregister(struct kunit *test, struct device *dev)
 	const struct device_driver *driver = to_kunit_device(dev)->driver;
 
 	kunit_release_action(test, device_unregister_wrapper, dev);
-	if (driver)
+	if (driver) {
+		const char *driver_name = driver->name;
 		kunit_release_action(test, driver_unregister_wrapper, (void *)driver);
+		kunit_kfree_const(test, driver_name);
+	}
 }
 EXPORT_SYMBOL_GPL(kunit_device_unregister);
 
-- 
2.46.0.rc1.232.g9752f9e123-goog