[PATCH] kunit: test_dev_action: Correctly cast 'priv' pointer to long*

[Florian Schmaus]

The previous implementation incorrectly assumed the original type of
'priv' was void**, leading to an unnecessary and misleading
cast. Correct the cast of the 'priv' pointer in test_dev_action() to
its actual type, long*, removing an unnecessary cast.

As an additional benefit, this fixes an out-of-bounds CHERI fault on
hardware with architectural capabilities. The original implementation
tried to store a capability-sized pointer using the 'priv'
pointer. However, the 'priv' pointer's capability only granted access
to the memory region of its original long type, leading to a bounds
violation since the size of a long is smaller than the size of a
capability. This change ensures that the pointer usage respects the
capabilities' bounds.

Signed-off-by: Florian Schmaus <florian...@codasip.com>
---
lib/kunit/kunit-test.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/kunit/kunit-test.c b/lib/kunit/kunit-test.c
index 8c01eabd4eaf..957b67818489 100644
--- a/lib/kunit/kunit-test.c
+++ b/lib/kunit/kunit-test.c
@@ -739,7 +739,7 @@ static struct kunit_case kunit_current_test_cases[] = {

static void test_dev_action(void *priv)
{
- *(void **)priv = (void *)1;
+ *(long*)priv = 1;
}

static void kunit_device_test(struct kunit *test)
--
2.51.0

[David Gow]

On Wed, 15 Oct 2025 at 15:23, Florian Schmaus
<florian...@codasip.com> wrote:
>
> The previous implementation incorrectly assumed the original type of
> 'priv' was void**, leading to an unnecessary and misleading
> cast. Correct the cast of the 'priv' pointer in test_dev_action() to
> its actual type, long*, removing an unnecessary cast.
>
> As an additional benefit, this fixes an out-of-bounds CHERI fault on
> hardware with architectural capabilities. The original implementation
> tried to store a capability-sized pointer using the 'priv'
> pointer. However, the 'priv' pointer's capability only granted access
> to the memory region of its original long type, leading to a bounds
> violation since the size of a long is smaller than the size of a
> capability. This change ensures that the pointer usage respects the
> capabilities' bounds.
>
> Signed-off-by: Florian Schmaus <florian...@codasip.com>
> ---

Thanks for this.

One simple formatting issue below, otherwise this is fine.

Also, it'd be good to add a 'Fixes' tag:
Fixes: d03c720e03bd ("kunit: Add APIs for managing devices")

Reviewed-by: David Gow <davi...@google.com>

Cheers,
-- David

> lib/kunit/kunit-test.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/kunit/kunit-test.c b/lib/kunit/kunit-test.c
> index 8c01eabd4eaf..957b67818489 100644
> --- a/lib/kunit/kunit-test.c
> +++ b/lib/kunit/kunit-test.c
> @@ -739,7 +739,7 @@ static struct kunit_case kunit_current_test_cases[] = {
>
> static void test_dev_action(void *priv)
> {
> - *(void **)priv = (void *)1;
> + *(long*)priv = 1;

checkpatch whinges here:
ERROR: "(foo*)" should be "(foo *)"
#39: FILE: lib/kunit/kunit-test.c:742:

[Florian Schmaus]

The previous implementation incorrectly assumed the original type of
'priv' was void**, leading to an unnecessary and misleading
cast. Correct the cast of the 'priv' pointer in test_dev_action() to
its actual type, long*, removing an unnecessary cast.

As an additional benefit, this fixes an out-of-bounds CHERI fault on
hardware with architectural capabilities. The original implementation
tried to store a capability-sized pointer using the priv
pointer. However, the priv pointer's capability only granted access to
the memory region of its original long type, leading to a bounds
violation since the size of a long is smaller than the size of a
capability. This change ensures that the pointer usage respects the
capabilities' bounds.

Fixes: d03c720e03bd ("kunit: Add APIs for managing devices")
Reviewed-by: David Gow <davi...@google.com>

Signed-off-by: Florian Schmaus <florian...@codasip.com>
---

Changes since v1:
- Fix simple formatting issue: long* -> long *
- Add 'Fixes' git trailer

lib/kunit/kunit-test.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/kunit/kunit-test.c b/lib/kunit/kunit-test.c

index 8c01eabd4eaf..63130a48e237 100644

--- a/lib/kunit/kunit-test.c
+++ b/lib/kunit/kunit-test.c
@@ -739,7 +739,7 @@ static struct kunit_case kunit_current_test_cases[] = {

static void test_dev_action(void *priv)
{
- *(void **)priv = (void *)1;

+ *(long *)priv = 1;