Message-ID: <CA+GJov5k2a6OEj-E2ULbimeMcY9Rq2Lh58-juBm=AMbPy0s4sA@mail.gmail.com>
Date: Fri, 2 Aug 2024 13:28:13 -0400
From: Rae Moar <rmoar@...gle.com>
To: David Gow <davidgow@...gle.com>
Cc: Brendan Higgins <brendan.higgins@...ux.dev>, Shuah Khan <skhan@...uxfoundation.org>, 
	Matti Vaittinen <mazziesaccount@...il.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Maxime Ripard <mripard@...nel.org>, Kees Cook <kees@...nel.org>, Nico Pache <npache@...hat.com>, 
	kunit-dev@...glegroups.com, linux-kselftest@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kunit: Device wrappers should also manage driver name

On Wed, Jul 31, 2024 at 3:02 AM David Gow <davidgow@...gle.com> wrote:
>
> 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@...hat.com>
> Closes: https://groups.google.com/g/kunit-dev/c/81V9b9QYON0
> Signed-off-by: David Gow <davidgow@...gle.com>
> Reviewed-by: Kees Cook <kees@...nel.org>
> ---
>
> There's some more serious changes since the RFC I sent, so please take a
> closer look.
>
> Thanks,
> -- David
>

Hello!

These changes look good to me. Fun patch to review! Only comment is
that we could potentially add tests for these functions in a future
patch.

Reviewed-by: Rae Moar <rmoar@...gle.com>

Thanks!
-Rae

> 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
>

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