Re: [PATCH v2 2/7] kunit: Fix kthread reference

[David Gow]

On Sat, 2 Mar 2024 at 03:40, Mickaël Salaün <mic@xxxxxxxxxxx> wrote:
>
> There is a race condition when a kthread finishes after the deadline and
> before the call to kthread_stop(), which may lead to use after free.
>
> Cc: Brendan Higgins <brendanhiggins@xxxxxxxxxx>
> Cc: David Gow <davidgow@xxxxxxxxxx>
> Cc: Rae Moar <rmoar@xxxxxxxxxx>
> Cc: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx>
> Link: https://lore.kernel.org/r/20240301194037.532117-3-mic@xxxxxxxxxxx
> ---

Thanks: I've never been unlucky enough to hit this, but it's definitely a bug.
We should ideally mark it with a fixes tag:
Fixes: adf505457032 ("kunit: fix UAF when run kfence test case test_gfpzero")

Reviewed-by: David Gow <davidgow@xxxxxxxxxx>

Cheers,
-- David

>
> Changes since v1:
> * Added Kees's Reviewed-by.
> ---
>  lib/kunit/try-catch.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/lib/kunit/try-catch.c b/lib/kunit/try-catch.c
> index a5cb2ef70a25..73f5007f20ea 100644
> --- a/lib/kunit/try-catch.c
> +++ b/lib/kunit/try-catch.c
> @@ -11,6 +11,7 @@
>  #include <linux/completion.h>
>  #include <linux/kernel.h>
>  #include <linux/kthread.h>
> +#include <linux/sched/task.h>
>
>  #include "try-catch-impl.h"
>
> @@ -65,14 +66,15 @@ void kunit_try_catch_run(struct kunit_try_catch *try_catch, void *context)
>         try_catch->context = context;
>         try_catch->try_completion = &try_completion;
>         try_catch->try_result = 0;
> -       task_struct = kthread_run(kunit_generic_run_threadfn_adapter,
> -                                 try_catch,
> -                                 "kunit_try_catch_thread");
> +       task_struct = kthread_create(kunit_generic_run_threadfn_adapter,
> +                                    try_catch, "kunit_try_catch_thread");
>         if (IS_ERR(task_struct)) {
>                 try_catch->try_result = PTR_ERR(task_struct);
>                 try_catch->catch(try_catch->context);
>                 return;
>         }
> +       get_task_struct(task_struct);
> +       wake_up_process(task_struct);
>
>         time_remaining = wait_for_completion_timeout(&try_completion,
>                                                      kunit_test_timeout());
> @@ -82,6 +84,7 @@ void kunit_try_catch_run(struct kunit_try_catch *try_catch, void *context)
>                 kthread_stop(task_struct);
>         }
>
> +       put_task_struct(task_struct);
>         exit_code = try_catch->try_result;
>
>         if (!exit_code)
> --
> 2.44.0
>

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