linux-kernel - Re: [PATCH] binder: fix potential UAF of target

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Date:   Tue, 17 May 2022 12:18:34 -0700
From:   Todd Kjos <tkjos@...gle.com>
To:     Carlos Llamas <cmllamas@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Christian Brauner <brauner@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Hridya Valsaraju <hridya@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        kernel-team@...roid.com, linux-kernel@...r.kernel.org,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH] binder: fix potential UAF of target_{proc,thread}

On Tue, May 17, 2022 at 11:58 AM Carlos Llamas <cmllamas@...gle.com> wrote:
>
> Commit 9474be34a727 ("binder: add failed transaction logging info")
> dereferences target_{proc,thread} after they have been potentially
> freed by binder_proc_dec_tmpref() and binder_thread_dec_tmpref().
>
> This patch delays the release of the two references after their last
> usage. Fixes the following two errors reported by smatch:
>
>   drivers/android/binder.c:3562 binder_transaction() error: dereferencing freed memory 'target_proc'
>   drivers/android/binder.c:3563 binder_transaction() error: dereferencing freed memory 'target_thread'
>
> Fixes: 9474be34a727 ("binder: add failed transaction logging info")
> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> Signed-off-by: Carlos Llamas <cmllamas@...gle.com>

Acked-by: Todd Kjos <tkjos@...gle.com>

> ---
>  drivers/android/binder.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index d9253b2a7bd9..83facfa1a5c3 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -3546,10 +3546,6 @@ static void binder_transaction(struct binder_proc *proc,
>  err_empty_call_stack:
>  err_dead_binder:
>  err_invalid_target_handle:
> -       if (target_thread)
> -               binder_thread_dec_tmpref(target_thread);
> -       if (target_proc)
> -               binder_proc_dec_tmpref(target_proc);
>         if (target_node) {
>                 binder_dec_node(target_node, 1, 0);
>                 binder_dec_node_tmpref(target_node);
> @@ -3565,6 +3561,11 @@ static void binder_transaction(struct binder_proc *proc,
>                      (u64)tr->data_size, (u64)tr->offsets_size,
>                      return_error_line);
>
> +       if (target_thread)
> +               binder_thread_dec_tmpref(target_thread);
> +       if (target_proc)
> +               binder_proc_dec_tmpref(target_proc);
> +
>         {
>                 struct binder_transaction_log_entry *fe;
>
> --
> 2.36.0.550.gb090851708-goog
>