Re: [PATCH] tracing: Do not call trigger_data_free with NULL data pointer

[Steven Rostedt]

On Thu,  5 Mar 2026 08:36:33 -0800
Guenter Roeck <linux@xxxxxxxxxxxx> wrote:

> If trigger_data_alloc() fails and returns NULL, event_hist_trigger_parse()
> jumps to the out_free error path. While kfree() safely handles a NULL
> pointer, trigger_data_free() does not. This causes a NULL pointer
> dereference in trigger_data_free() when evaluating
> data->cmd_ops->set_filter.
> 
> Fix the problem by adding a new goto label and jumping to it if
> trigger_data_alloc() returns NULL.
> 
> The problem was found by an experimental code review agent based on
> gemini-3.1-pro while reviewing backports into v6.18.y.
> 
> Assisted-by: Gemini:gemini-3.1-pro
> Cc: Miaoqian Lin <linmq006@xxxxxxxxx>
> Cc: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> Fixes: 0550069cc25f ("tracing: Properly process error handling in event_hist_trigger_parse()")
> Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> ---
>  kernel/trace/trace_events_hist.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 73ea180cad55..a2abdfe19281 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -6874,7 +6874,7 @@ static int event_hist_trigger_parse(struct event_command *cmd_ops,
>  	trigger_data = trigger_data_alloc(cmd_ops, cmd, param, hist_data);
>  	if (!trigger_data) {
>  		ret = -ENOMEM;
> -		goto out_free;
> +		goto out_destroy;
>  	}
>  
>  	ret = event_trigger_set_filter(cmd_ops, file, filter, trigger_data);
> @@ -6942,7 +6942,7 @@ static int event_hist_trigger_parse(struct event_command *cmd_ops,
>  	remove_hist_vars(hist_data);
>  
>  	trigger_data_free(trigger_data);

I rather make trigger_data_free() more robust by starting it with:

	if (!data)
		return;

-- Steve

> -
> +out_destroy:
>  	destroy_hist_data(hist_data);
>  	goto out;
>  }