Re: [PATCH 1/4] binder: fix node UAF in binder_add_freeze_work()

[Todd Kjos]

On Tue, Sep 24, 2024 at 11:44 AM Carlos Llamas <cmllamas@xxxxxxxxxx> wrote:
>
> In binder_add_freeze_work() we iterate over the proc->nodes with the
> proc->inner_lock held. However, this lock is temporarily dropped in
> order to acquire the node->lock first (lock nesting order). This can
> race with binder_node_release() and trigger a use-after-free:
>
>   ==================================================================
>   BUG: KASAN: slab-use-after-free in _raw_spin_lock+0xe4/0x19c
>   Write of size 4 at addr ffff53c04c29dd04 by task freeze/640
>
>   CPU: 5 UID: 0 PID: 640 Comm: freeze Not tainted 6.11.0-07343-ga727812a8d45 #17
>   Hardware name: linux,dummy-virt (DT)
>   Call trace:
>    _raw_spin_lock+0xe4/0x19c
>    binder_add_freeze_work+0x148/0x478
>    binder_ioctl+0x1e70/0x25ac
>    __arm64_sys_ioctl+0x124/0x190
>
>   Allocated by task 637:
>    __kmalloc_cache_noprof+0x12c/0x27c
>    binder_new_node+0x50/0x700
>    binder_transaction+0x35ac/0x6f74
>    binder_thread_write+0xfb8/0x42a0
>    binder_ioctl+0x18f0/0x25ac
>    __arm64_sys_ioctl+0x124/0x190
>
>   Freed by task 637:
>    kfree+0xf0/0x330
>    binder_thread_read+0x1e88/0x3a68
>    binder_ioctl+0x16d8/0x25ac
>    __arm64_sys_ioctl+0x124/0x190
>   ==================================================================
>
> Fix the race by taking a temporary reference on the node before
> releasing the proc->inner lock. This ensures the node remains alive
> while in use.
>
> Fixes: d579b04a52a1 ("binder: frozen notification")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Carlos Llamas <cmllamas@xxxxxxxxxx>

Acked-by: Todd Kjos <tkjos@xxxxxxxxxx>

> ---
>  drivers/android/binder.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index 978740537a1a..4d90203ea048 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -5552,6 +5552,7 @@ static bool binder_txns_pending_ilocked(struct binder_proc *proc)
>
>  static void binder_add_freeze_work(struct binder_proc *proc, bool is_frozen)
>  {
> +       struct binder_node *prev = NULL;
>         struct rb_node *n;
>         struct binder_ref *ref;
>
> @@ -5560,7 +5561,10 @@ static void binder_add_freeze_work(struct binder_proc *proc, bool is_frozen)
>                 struct binder_node *node;
>
>                 node = rb_entry(n, struct binder_node, rb_node);
> +               binder_inc_node_tmpref_ilocked(node);
>                 binder_inner_proc_unlock(proc);
> +               if (prev)
> +                       binder_put_node(prev);
>                 binder_node_lock(node);
>                 hlist_for_each_entry(ref, &node->refs, node_entry) {
>                         /*
> @@ -5586,10 +5590,13 @@ static void binder_add_freeze_work(struct binder_proc *proc, bool is_frozen)
>                         }
>                         binder_inner_proc_unlock(ref->proc);
>                 }
> +               prev = node;
>                 binder_node_unlock(node);
>                 binder_inner_proc_lock(proc);
>         }
>         binder_inner_proc_unlock(proc);
> +       if (prev)
> +               binder_put_node(prev);
>  }
>
>  static int binder_ioctl_freeze(struct binder_freeze_info *info,
> --
> 2.46.0.792.g87dc391469-goog
>