binder: use current_euid() for transaction sender identity

Binder currently uses task_euid(proc->tsk) as the transaction sender EUID,
where proc->tsk is the main thread of the process that opened /dev/binder.
That's not clean; use the subjective EUID of the current task instead.

Signed-off-by: Jann Horn <[email protected]>
Reviewed-by: Alice Ryhl <[email protected]>
Acked-by: Gary Guo <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

drivers/android/binder.c

@@ -3117,7 +3117,7 @@ static void binder_transaction(struct binder_proc *proc,
 	t->start_time = t_start_time;
 	t->from_pid = proc->pid;
 	t->from_tid = thread->pid;
-	t->sender_euid = task_euid(proc->tsk);
+	t->sender_euid = current_euid();
 	t->code = tr->code;
 	t->flags = tr->flags;
 	t->priority = task_nice(current);