Re: [PATCH 3/4] binder: fix freeze UAF in binder_release_work()

[Todd Kjos]

On Tue, Sep 24, 2024 at 11:44 AM Carlos Llamas <cmllamas@xxxxxxxxxx> wrote:
>
> When a binder reference is cleaned up, any freeze work queued in the
> associated process should also be removed. Otherwise, the reference is
> freed while its ref->freeze.work is still queued in proc->work leading
> to a use-after-free issue as shown by the following KASAN report:
>
>   ==================================================================
>   BUG: KASAN: slab-use-after-free in binder_release_work+0x398/0x3d0
>   Read of size 8 at addr ffff31600ee91488 by task kworker/5:1/211
>
>   CPU: 5 UID: 0 PID: 211 Comm: kworker/5:1 Not tainted 6.11.0-rc7-00382-gfc6c92196396 #22
>   Hardware name: linux,dummy-virt (DT)
>   Workqueue: events binder_deferred_func
>   Call trace:
>    binder_release_work+0x398/0x3d0
>    binder_deferred_func+0xb60/0x109c
>    process_one_work+0x51c/0xbd4
>    worker_thread+0x608/0xee8
>
>   Allocated by task 703:
>    __kmalloc_cache_noprof+0x130/0x280
>    binder_thread_write+0xdb4/0x42a0
>    binder_ioctl+0x18f0/0x25ac
>    __arm64_sys_ioctl+0x124/0x190
>    invoke_syscall+0x6c/0x254
>
>   Freed by task 211:
>    kfree+0xc4/0x230
>    binder_deferred_func+0xae8/0x109c
>    process_one_work+0x51c/0xbd4
>    worker_thread+0x608/0xee8
>   ==================================================================
>
> This commit fixes the issue by ensuring any queued freeze work is removed
> when cleaning up a binder reference.
>
> Fixes: d579b04a52a1 ("binder: frozen notification")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Carlos Llamas <cmllamas@xxxxxxxxxx>

Acked-by: Todd Kjos <tkjos@xxxxxxxxxxx>

> ---
>  drivers/android/binder.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index 8bca2de6fa24..d955135ee37a 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -1225,6 +1225,12 @@ static void binder_cleanup_ref_olocked(struct binder_ref *ref)
>                 binder_dequeue_work(ref->proc, &ref->death->work);
>                 binder_stats_deleted(BINDER_STAT_DEATH);
>         }
> +
> +       if (ref->freeze) {
> +               binder_dequeue_work(ref->proc, &ref->freeze->work);
> +               binder_stats_deleted(BINDER_STAT_FREEZE);
> +       }
> +
>         binder_stats_deleted(BINDER_STAT_REF);
>  }
>
> --
> 2.46.0.792.g87dc391469-goog
>