Re: [PATCH v2 1/2] tracing/hist: rebuild full_name on each hist_field_name() call

[Steven Rostedt]

Tom,

On Wed,  1 Apr 2026 19:22:23 +0800
Pengpeng Hou <pengpeng@xxxxxxxxxxx> wrote:

> hist_field_name() uses a static MAX_FILTER_STR_VAL buffer for fully
> qualified variable-reference names, but it currently appends into that
> buffer with strcat() without rebuilding it first. As a result, repeated
> calls append a new "system.event.field" name onto the previous one,
> which can eventually run past the end of full_name.
> 
> Build the name with snprintf() on each call and return NULL if the fully
> qualified name does not fit in MAX_FILTER_STR_VAL.
> 
> Fixes: 067fe038e70f ("tracing: Add variable reference handling to hist triggers")
> Signed-off-by: Pengpeng Hou <pengpeng@xxxxxxxxxxx>
> ---
> Changes since v1: https://lore.kernel.org/all/20260329030950.32503-1-pengpeng@xxxxxxxxxxx/
> 
> - rebuild full_name on each call instead of falling back to field->name
> - return NULL on overflow as suggested
> - split out the snprintf() length check instead of using an inline if
> 
>  kernel/trace/trace_events_hist.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 73ea180cad55..f9c8a4f078ea 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -1361,12 +1361,14 @@ static const char *hist_field_name(struct hist_field *field,
>  		 field->flags & HIST_FIELD_FL_VAR_REF) {
>  		if (field->system) {
>  			static char full_name[MAX_FILTER_STR_VAL];
> +			int len;
> +
> +			len = snprintf(full_name, sizeof(full_name), "%s.%s.%s",
> +				       field->system, field->event_name,
> +				       field->name);
> +			if (len >= sizeof(full_name))
> +				return NULL;
>  
> -			strcat(full_name, field->system);
> -			strcat(full_name, ".");
> -			strcat(full_name, field->event_name);
> -			strcat(full_name, ".");
> -			strcat(full_name, field->name);
>  			field_name = full_name;

I wanted to test this but I can't find anything that triggers this path.
How does a field here get its ->system set?

If there's no way to hit this path, I much rather remove it than "fix" it.

-- Steve


>  		} else
>  			field_name = field->name;