Re: [PATCH v2] kunit: fix reference count leak in kfree_at_end

[Daniel Latypov]

On Thu, Sep 9, 2021 at 9:59 AM Daniel Latypov <dlatypov@xxxxxxxxxx> wrote:
>
> On Thu, Sep 9, 2021 at 12:26 AM 'Xiyu Yang' via KUnit Development
> <kunit-dev@xxxxxxxxxxxxxxxx> wrote:
> >
> > The reference counting issue happens in the normal path of
> > kfree_at_end(). When kunit_alloc_and_get_resource() is invoked, the
> > function forgets to handle the returned resource object, whose refcount
> > increased inside, causing a refcount leak.
> >
> > Fix this issue by calling kunit_alloc_resource() instead of
> > kunit_alloc_and_get_resource().
> >
> > Signed-off-by: Xiyu Yang <xiyuyang19@xxxxxxxxxxxx>
> > Signed-off-by: Xin Tan <tanxin.ctf@xxxxxxxxx>
>
> Reviewed-by: Daniel Latypov <dlatypov@xxxxxxxxxx>
>
> Ah, thanks for finding and fixing this!
> We really should have better documentation/otherwise make it clearer
> that people shouldn't use the "_and_get" version.
>
> I went and added some pr_info() calls to verify that these were being
> leaked before and they're fixed now.
>
> I copy-pasted this mistake into
> https://lore.kernel.org/linux-kselftest/20210831171926.3832806-2-dlatypov@xxxxxxxxxx/.
> I'll send a v3 fix for that patch as well.

Fixed that patch:
https://lore.kernel.org/linux-kselftest/20210909171052.3192326-2-dlatypov@xxxxxxxxxx/

I assume this patch and that one shouldn't have merge conflicts, so we
don't need these to be applied in any specific order.

>
> > ---
> >  lib/kunit/executor_test.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/lib/kunit/executor_test.c b/lib/kunit/executor_test.c
> > index cdbe54b16501..c2dcfb1f6e97 100644
> > --- a/lib/kunit/executor_test.c
> > +++ b/lib/kunit/executor_test.c
> > @@ -116,7 +116,7 @@ static void kfree_at_end(struct kunit *test, const void *to_free)
> >         /* kfree() handles NULL already, but avoid allocating a no-op cleanup. */
> >         if (IS_ERR_OR_NULL(to_free))
> >                 return;
> > -       kunit_alloc_and_get_resource(test, NULL, kfree_res_free, GFP_KERNEL,
> > +       kunit_alloc_resource(test, NULL, kfree_res_free, GFP_KERNEL,
> >                                      (void *)to_free);
> >  }
> >
> > --
> > 2.7.4
> >
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