Re: [PATCH] binder: fix potential UAF of target_{proc,thread}

[Todd Kjos]

On Tue, May 17, 2022 at 11:58 AM Carlos Llamas <cmllamas@xxxxxxxxxx> 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@xxxxxxxxxx>
> Signed-off-by: Carlos Llamas <cmllamas@xxxxxxxxxx>

Acked-by: Todd Kjos <tkjos@xxxxxxxxxx>

> ---
>  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
>