On Tue, Aug 02, 2022 at 07:40:32PM +0000, Carlos Llamas wrote:

On Mon, Aug 01, 2022 at 06:25:11PM +0000, Carlos Llamas wrote:

...

A transaction of type BINDER_TYPE_WEAK_HANDLE can fail to increment the reference for a node. In this case, the target proc normally releases the failed reference upon close as expected. However, if the target is dying in parallel the call will race with binder_deferred_release(), so the target could have released all of its references by now leaving the cleanup of the new failed reference unhandled.

The transaction then ends and the target proc gets released making the ref->proc now a dangling pointer. Later on, ref->node is closed and we attempt to take spin_lock(&ref->proc->inner_lock), which leads to the use-after-free bug reported below. Let's fix this by cleaning up the failed reference on the spot instead of relying on the target to do so.

================================================================== BUG: KASAN: use-after-free in _raw_spin_lock+0xa8/0x150 Write of size 4 at addr ffff5ca207094238 by task kworker/1:0/590

CPU: 1 PID: 590 Comm: kworker/1:0 Not tainted 5.19.0-rc8 #10 Hardware name: linux,dummy-virt (DT) Workqueue: events binder_deferred_func Call trace: dump_backtrace.part.0+0x1d0/0x1e0 show_stack+0x18/0x70 dump_stack_lvl+0x68/0x84 print_report+0x2e4/0x61c kasan_report+0xa4/0x110 kasan_check_range+0xfc/0x1a4 __kasan_check_write+0x3c/0x50 _raw_spin_lock+0xa8/0x150 binder_deferred_func+0x5e0/0x9b0 process_one_work+0x38c/0x5f0 worker_thread+0x9c/0x694 kthread+0x188/0x190 ret_from_fork+0x10/0x20

Signed-off-by: Carlos Llamas cmllamas@google.com

drivers/android/binder.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 362c0deb65f1..9d42afe60180 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -1361,6 +1361,18 @@ static int binder_inc_ref_for_node(struct binder_proc *proc, } ret = binder_inc_ref_olocked(ref, strong, target_list); *rdata = ref->data;

• if (ret && ref == new_ref) {

• /*
  

•  * Cleanup the failed reference here as the target
  

•  * could now be dead and have already released its
  

•  * references by now. Calling on the new reference
  

•  * with strong=0 and a tmp_refs will not decrement
  

•  * the node. The new_ref gets kfree'd below.
  

•  */
  

• binder_cleanup_ref_olocked(new_ref);
  

• ref = NULL;
  

• }
• binder_proc_unlock(proc); if (new_ref && ref != new_ref) /*

-- 2.37.1.455.g008518b4e5-goog

Sorry, I forgot to CC stable. This patch should be applied to all stable kernels starting with 4.14 and higher.

Cc: stable@vger.kernel.org # 4.14+

Thanks, I'll add this when I queue it up after 5.20-rc1 is out.

greg k-h