Skip to content
Commit f3277cbf authored by Todd Kjos's avatar Todd Kjos Committed by Greg Kroah-Hartman
Browse files

binder: fix UAF when releasing todo list



When releasing a thread todo list when tearing down
a binder_proc, the following race was possible which
could result in a use-after-free:

1.  Thread 1: enter binder_release_work from binder_thread_release
2.  Thread 2: binder_update_ref_for_handle() -> binder_dec_node_ilocked()
3.  Thread 2: dec nodeA --> 0 (will free node)
4.  Thread 1: ACQ inner_proc_lock
5.  Thread 2: block on inner_proc_lock
6.  Thread 1: dequeue work (BINDER_WORK_NODE, part of nodeA)
7.  Thread 1: REL inner_proc_lock
8.  Thread 2: ACQ inner_proc_lock
9.  Thread 2: todo list cleanup, but work was already dequeued
10. Thread 2: free node
11. Thread 2: REL inner_proc_lock
12. Thread 1: deref w->type (UAF)

The problem was that for a BINDER_WORK_NODE, the binder_work element
must not be accessed after releasing the inner_proc_lock while
processing the todo list elements since another thread might be
handling a deref on the node containing the binder_work element
leading to the node being freed.

Signed-off-by: default avatarTodd Kjos <tkjos@google.com>
Link: https://lore.kernel.org/r/20201009232455.4054810-1-tkjos@google.com


Cc: <stable@vger.kernel.org> # 4.14, 4.19, 5.4, 5.8
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 78eef5d9
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment