CVE-2025-21899

In the Linux kernel, the following vulnerability has been resolved:

tracing: Fix bad hist from corrupting named_triggers list

The following commands causes a crash:

~# cd /sys/kernel/tracing/events/rcu/rcu_callback ~# echo 'hist:name=bad:keys=common_pid:onmax(bogus).save(common_pid)' > trigger bash: echo: write error: Invalid argument ~# echo 'hist:name=bad:keys=common_pid' > trigger

Because the following occurs:

event_trigger_write() { trigger_process_regex() { event_hist_trigger_parse() {

  data = event_trigger_alloc(..);

  event_trigger_register(.., data) {
    cmd_ops->reg(.., data, ..) [hist_register_trigger()] {
      data->ops->init() [event_hist_trigger_init()] {
        save_named_trigger(name, data) {
          list_add(&data->named_list, &named_triggers);
        }
      }
    }
  }

  ret = create_actions(); (return -EINVAL)
  if (ret)
    goto out_unreg;

[..] ret = hist_trigger_enable(data, ...) { list_add_tail_rcu(&data->list, &file->triggers); <<<---- SKIPPED!!! (this is important!) [..] out_unreg: event_hist_unregister(.., data) { cmd_ops->unreg(.., data, ..) [hist_unregister_trigger()] { list_for_each_entry(iter, &file->triggers, list) { if (!hist_trigger_match(data, iter, named_data, false)) <- never matches continue; [..] test = iter; } if (test && test->ops->free) <<<-- test is NULL

        test->ops->free(test) [event_hist_trigger_free()] {
          [..]
          if (data->name)
            del_named_trigger(data) {
              list_del(&data->named_list);  <<<<-- NEVER gets removed!
            }
          }
       }
     }

     [..]
     kfree(data); <<<-- frees item but it is still on list

The next time a hist with name is registered, it causes an u-a-f bug and the kernel can crash.

Move the code around such...