Re: [PATCH] tracing: Fix bad hist from corrupting named_triggers list

[Tom Zanussi <zanussi@kernel.org>]

Hi Steve,

On Tue, 2025-02-25 at 12:53 -0500, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@goodmis.org>
> 
> 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 that if event_trigger_register() succeeds, the
> next thing called is hist_trigger_enable() which adds it to the list.
> 
> A bunch of actions is called if get_named_trigger_data() returns false.
> But that doesn't need to be called after event_trigger_register(), so it
> can be moved up, allowing event_trigger_register() to be called just
> before hist_trigger_enable() keeping them together and allowing the
> file->triggers to be properly populated.
> 
> Cc: stable@vger.kernel.org
> Fixes: 067fe038e70f6 ("tracing: Add variable reference handling to hist triggers")
> Reported-by: Tomas Glozar <tglozar@redhat.com>
> Closes: https://lore.kernel.org/all/CAP4=nvTsxjckSBTz=Oe_UYh8keD9_sZC4i++4h72mJLic4_W4A@mail.gmail.com/
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Looks like a good fix, and is cleaner without the goto as well. Small typo below...

Reviewed-by: Tom Zanussi <zanussi@kernel.org>


> ---
>  kernel/trace/trace_events_hist.c | 31 ++++++++++++++++---------------
>  1 file changed, 16 insertions(+), 15 deletions(-)
> 
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 261163b00137..c32adc372808 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -6724,27 +6724,28 @@ static int event_hist_trigger_parse(struct event_command *cmd_ops,
>  	if (existing_hist_update_only(glob, trigger_data, file))
>  		goto out_free;
>  
> -	ret = event_trigger_register(cmd_ops, file, glob, trigger_data);
> -	if (ret < 0)
> -		goto out_free;
> +	if (!get_named_trigger_data(trigger_data)) {
>  
> -	if (get_named_trigger_data(trigger_data))
> -		goto enable;
> +		ret = create_actions(hist_data);
> +		if (ret)
> +			goto out_free;
>  
> -	ret = create_actions(hist_data);
> -	if (ret)
> -		goto out_unreg;
> +		if (has_hist_vars(hist_data) || hist_data->n_var_refs) {
> +			ret = save_hist_vars(hist_data);
> +			if (ret)
> +				goto out_free;
> +		}
>  
> -	if (has_hist_vars(hist_data) || hist_data->n_var_refs) {
> -		ret = save_hist_vars(hist_data);
> +		ret = tracing_map_init(hist_data->map);
>  		if (ret)
> -			goto out_unreg;
> +			goto out_free;
>  	}
>  
> -	ret = tracing_map_init(hist_data->map);
> -	if (ret)
> -		goto out_unreg;
> -enable:
> +	ret = event_trigger_register(cmd_ops, file, glob, trigger_data);
> +	if (ret < 0)
> +		goto out_free;
> +
> +

Extra space added here.

>  	ret = hist_trigger_enable(trigger_data, file);
>  	if (ret)
>  		goto out_unreg;

Thanks,

Tom