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

[Alice Ryhl]

On Tue, Sep 24, 2024 at 8:44 PM 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>

Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>