linux-kernel - Re: [PATCH] kunit: fix too small allocation when using suite-only kunit.filter

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Date:   Sat, 2 Oct 2021 10:30:23 +0800
From:   David Gow <davidgow@...gle.com>
To:     Daniel Latypov <dlatypov@...gle.com>
Cc:     Brendan Higgins <brendanhiggins@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        KUnit Development <kunit-dev@...glegroups.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        kernel test robot <oliver.sang@...el.com>
Subject: Re: [PATCH] kunit: fix too small allocation when using suite-only kunit.filter_glob

On Sat, Oct 2, 2021 at 9:36 AM Daniel Latypov <dlatypov@...gle.com> wrote:
>
> When a user filters by a suite and not a test, e.g.
> $ ./tools/testing/kunit/kunit.py run 'suite_name'
>
> it hits this code
>   const int len = strlen(filter_glob);
>   ...
>   parsed->suite_glob = kmalloc(len, GFP_KERNEL);
> which fails to allocate space for the terminating NULL.
>
> Somehow, it seems like we can't easily reproduce this under UML, so the
> existing `parse_filter_test()` didn't catch this.
>
> Fix this by allocating `len + 1` and switch to kzalloc() just to be a
> bit more defensive. We're only going to run this code once per kernel
> boot, and it should never be very long.
>
> Also update the unit tests to be a bit more cautious.
> This bug showed up as a NULL pointer dereference here:
> >  KUNIT_EXPECT_STREQ(test, (const char *)filtered.start[0][0]->name, "suite0");
> `filtered.start[0][0]` was NULL, and `name` is at offset 0 in the struct,
> so `...->name` was also NULL.
>
> Fixes: 3b29021ddd10 ("kunit: tool: allow filtering test cases via glob")
> Reported-by: kernel test robot <oliver.sang@...el.com>
> Signed-off-by: Daniel Latypov <dlatypov@...gle.com>
> ---

Nice catch. I guess this is why we're all going to be switching to
rust one day. :-)

The fix looks good, and I ran it under KASAN just to be sure, and it passed.

Reviewed-by: David Gow <davidgow@...gle.com>

-- David

>  lib/kunit/executor.c      | 2 +-
>  lib/kunit/executor_test.c | 1 +
>  2 files changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/lib/kunit/executor.c b/lib/kunit/executor.c
> index bab3ab940acc..1d7fecd33261 100644
> --- a/lib/kunit/executor.c
> +++ b/lib/kunit/executor.c
> @@ -33,7 +33,7 @@ static void kunit_parse_filter_glob(struct kunit_test_filter *parsed,
>         const char *period = strchr(filter_glob, '.');
>
>         if (!period) {
> -               parsed->suite_glob = kmalloc(len, GFP_KERNEL);
> +               parsed->suite_glob = kzalloc(len + 1, GFP_KERNEL);
>                 parsed->test_glob = NULL;
>                 strcpy(parsed->suite_glob, filter_glob);
>                 return;
> diff --git a/lib/kunit/executor_test.c b/lib/kunit/executor_test.c
> index e6323f398dfa..7d2b8dc668b1 100644
> --- a/lib/kunit/executor_test.c
> +++ b/lib/kunit/executor_test.c
> @@ -149,6 +149,7 @@ static void filter_suites_test(struct kunit *test)
>
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, filtered.start);
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, filtered.start[0]);
> +       KUNIT_ASSERT_NOT_ERR_OR_NULL(test, filtered.start[0][0]);
>         KUNIT_EXPECT_STREQ(test, (const char *)filtered.start[0][0]->name, "suite0");
>  }
>
>
> base-commit: 3b29021ddd10cfb6b2565c623595bd3b02036f33
> --
> 2.33.0.800.g4c38ced690-goog
>