From: Todd Kjos tkjos@google.com
commit f3277cbfba763cd2826396521b9296de67cf1bbc upstream.
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: Todd 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: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/android/binder.c | 35 ++++++++++------------------------- 1 file changed, 10 insertions(+), 25 deletions(-)
--- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -285,7 +285,7 @@ struct binder_device { struct binder_work { struct list_head entry;
- enum { + enum binder_work_type { BINDER_WORK_TRANSACTION = 1, BINDER_WORK_TRANSACTION_COMPLETE, BINDER_WORK_RETURN_ERROR, @@ -895,27 +895,6 @@ static struct binder_work *binder_dequeu return w; }
-/** - * binder_dequeue_work_head() - Dequeues the item at head of list - * @proc: binder_proc associated with list - * @list: list to dequeue head - * - * Removes the head of the list if there are items on the list - * - * Return: pointer dequeued binder_work, NULL if list was empty - */ -static struct binder_work *binder_dequeue_work_head( - struct binder_proc *proc, - struct list_head *list) -{ - struct binder_work *w; - - binder_inner_proc_lock(proc); - w = binder_dequeue_work_head_ilocked(list); - binder_inner_proc_unlock(proc); - return w; -} - static void binder_defer_work(struct binder_proc *proc, enum binder_deferred_state defer); static void binder_free_thread(struct binder_thread *thread); @@ -4242,13 +4221,17 @@ static void binder_release_work(struct b struct list_head *list) { struct binder_work *w; + enum binder_work_type wtype;
while (1) { - w = binder_dequeue_work_head(proc, list); + binder_inner_proc_lock(proc); + w = binder_dequeue_work_head_ilocked(list); + wtype = w ? w->type : 0; + binder_inner_proc_unlock(proc); if (!w) return;
- switch (w->type) { + switch (wtype) { case BINDER_WORK_TRANSACTION: { struct binder_transaction *t;
@@ -4282,9 +4265,11 @@ static void binder_release_work(struct b kfree(death); binder_stats_deleted(BINDER_STAT_DEATH); } break; + case BINDER_WORK_NODE: + break; default: pr_err("unexpected work type, %d, not freed\n", - w->type); + wtype); break; } }