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

[Guenter Roeck]

On Thu, Mar 05, 2026 at 11:43:36AM -0500, Steven Rostedt wrote:
> 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;

Sure. No preference on my side. I'll send v2.

Thanks,
Guenter