Re: [PATCH v4] tracing: Bound synthetic-field strings with seq_buf

[Steven Rostedt]

On Fri, 17 Apr 2026 20:20:00 +0800
Pengpeng Hou <pengpeng@xxxxxxxxxxx> wrote:

> @ -2962,14 +2963,22 @@ find_synthetic_field_var(struct hist_trigger_data *target_hist_data,
>  			 char *system, char *event_name, char *field_name)
>  {
>  	struct hist_field *event_var;
> +	struct seq_buf s;
>  	char *synthetic_name;
>  
>  	synthetic_name = kzalloc(MAX_FILTER_STR_VAL, GFP_KERNEL);
>  	if (!synthetic_name)
>  		return ERR_PTR(-ENOMEM);
>  
> -	strcpy(synthetic_name, "synthetic_");
> -	strcat(synthetic_name, field_name);
> +	seq_buf_init(&s, synthetic_name, MAX_FILTER_STR_VAL);
> +	seq_buf_puts(&s, "synthetic_");
> +	seq_buf_puts(&s, field_name);

newline

> +	/* Terminate synthetic_name with a NUL. */
> +	seq_buf_str(&s);

newline

> +	if (seq_buf_has_overflowed(&s)) {
> +		kfree(synthetic_name);
> +		return ERR_PTR(-E2BIG);
> +	}
>  
>  	event_var = find_event_var(target_hist_data, system, event_name, synthetic_name);
>  
> @@ -3014,7 +3023,7 @@ create_field_var_hist(struct hist_trigger_data *target_hist_data,
>  	struct trace_event_file *file;
>  	struct hist_field *key_field;
>  	struct hist_field *event_var;
> -	char *saved_filter;
> +	struct seq_buf s;
>  	char *cmd;
>  	int ret;
>  
> @@ -3059,28 +3068,35 @@ create_field_var_hist(struct hist_trigger_data *target_hist_data,
>  		return ERR_PTR(-ENOMEM);
>  	}
>  
> +	seq_buf_init(&s, cmd, MAX_FILTER_STR_VAL);
> +
>  	/* Use the same keys as the compatible histogram */
> -	strcat(cmd, "keys=");
> +	seq_buf_puts(&s, "keys=");
>  
>  	for_each_hist_key_field(i, hist_data) {
>  		key_field = hist_data->fields[i];
>  		if (!first)
> -			strcat(cmd, ",");
> -		strcat(cmd, key_field->field->name);
> +			seq_buf_putc(&s, ',');
> +		seq_buf_puts(&s, key_field->field->name);
>  		first = false;
>  	}
>  
>  	/* Create the synthetic field variable specification */
> -	strcat(cmd, ":synthetic_");
> -	strcat(cmd, field_name);
> -	strcat(cmd, "=");
> -	strcat(cmd, field_name);
> +	seq_buf_printf(&s, ":synthetic_%s=%s", field_name, field_name);
>  
>  	/* Use the same filter as the compatible histogram */
> -	saved_filter = find_trigger_filter(hist_data, file);
> -	if (saved_filter) {
> -		strcat(cmd, " if ");
> -		strcat(cmd, saved_filter);
> +	{
> +		char *saved_filter = find_trigger_filter(hist_data, file);
> +
> +		if (saved_filter)
> +			seq_buf_printf(&s, " if %s", saved_filter);
> +	}
> +

Different function. Should have the comment about adding nul here too.

> +	seq_buf_str(&s);

newline

> +	if (seq_buf_has_overflowed(&s)) {
> +		kfree(cmd);
> +		kfree(var_hist);
> +		return ERR_PTR(-E2BIG);
>  	}

-- Steve