linux-kernel - Re: [PATCH v2 4/5] kunit: make kunit_kfree() not segfault on invalid inputs

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Date:   Wed, 5 Oct 2022 16:39:14 -0400
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     Daniel Latypov <dlatypov@...gle.com>
Cc:     davidgow@...gle.com, linux-kernel@...r.kernel.org,
        kunit-dev@...glegroups.com, linux-kselftest@...r.kernel.org,
        skhan@...uxfoundation.org
Subject: Re: [PATCH v2 4/5] kunit: make kunit_kfree() not segfault on invalid inputs

On Fri, Jul 22, 2022 at 1:15 PM Daniel Latypov <dlatypov@...gle.com> wrote:
>
> kunit_kfree() can only work on data ("resources") allocated by KUnit.
>
> Currently for code like this,
> > void *ptr = kmalloc(4, GFP_KERNEL);
> > kunit_kfree(test, ptr);
> kunit_kfree() will segfault.
>
> It'll try and look up the kunit_resource associated with `ptr` and get a
> NULL back, but it won't check for this. This means we also segfault if
> you double-free.
>
> Change kunit_kfree() so it'll notice these invalid pointers and respond
> by failing the test.
>
> Implementation: kunit_destroy_resource() does what kunit_kfree() does,
> but is more generic and returns -ENOENT when it can't find the resource.
> Sadly, unlike just letting it crash, this means we don't get a stack
> trace. But kunit_kfree() is so infrequently used it shouldn't be hard to
> track down the bad callsite anyways.
>
> After this change, the above code gives:
> > # example_simple_test: EXPECTATION FAILED at lib/kunit/test.c:702
> > kunit_kfree: 00000000626ec200 already freed or not allocated by kunit
>
> Signed-off-by: Daniel Latypov <dlatypov@...gle.com>
> Reviewed-by: David Gow <davidgow@...gle.com>

Reviewed-by: Brendan Higgins <brendanhiggins@...gle.com>