Re: [PATCH v2 2/2] tracing/hist: reject synthetic-field strings that exceed MAX_FILTER_STR_VAL

[Steven Rostedt <rostedt@goodmis.org>]

On Wed,  1 Apr 2026 19:22:24 +0800
Pengpeng Hou <pengpeng@iscas.ac.cn> wrote:

> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index f9c8a4f078ea..4172c91605af 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -2966,12 +2966,16 @@ find_synthetic_field_var(struct hist_trigger_data *target_hist_data,
>  	struct hist_field *event_var;
>  	char *synthetic_name;
>  
> +	if ((sizeof("synthetic_") - 1) + strlen(field_name) >=
> +	    MAX_FILTER_STR_VAL)
> +		return ERR_PTR(-E2BIG);
> +
>  	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);
> +	scnprintf(synthetic_name, MAX_FILTER_STR_VAL, "synthetic_%s",
> +		  field_name);
>  
>  	event_var = find_event_var(target_hist_data, system, event_name, synthetic_name);
>  
> @@ -3018,6 +3022,8 @@ create_field_var_hist(struct hist_trigger_data *target_hist_data,
>  	struct hist_field *event_var;
>  	char *saved_filter;
>  	char *cmd;
> +	size_t cmdlen;
> +	size_t off;
>  	int ret;
>  
>  	if (target_hist_data->n_field_var_hists >= SYNTH_FIELDS_MAX) {
> @@ -3048,13 +3054,36 @@ create_field_var_hist(struct hist_trigger_data *target_hist_data,
>  	/* See if a synthetic field variable has already been created */
>  	event_var = find_synthetic_field_var(target_hist_data, subsys_name,
>  					     event_name, field_name);
> -	if (!IS_ERR_OR_NULL(event_var))
> +	if (IS_ERR(event_var))
> +		return event_var;
> +	if (event_var)
>  		return event_var;
>  
>  	var_hist = kzalloc_obj(*var_hist);
>  	if (!var_hist)
>  		return ERR_PTR(-ENOMEM);
>  
> +	saved_filter = find_trigger_filter(hist_data, file);
> +
> +	cmdlen = strlen("keys=") + strlen(":synthetic_") +
> +		 strlen(field_name) + strlen("=") + strlen(field_name);

Instead of doing all this complex updates, let's use seq_buf in this patch
instead. That's what it's for.

I'll take patch 1 as is, just update this patch.

Thanks,

-- Steve


> +	first = true;
> +	for_each_hist_key_field(i, hist_data) {
> +		key_field = hist_data->fields[i];
> +		if (!first)
> +			cmdlen++;
> +		cmdlen += strlen(key_field->field->name);
> +		first = false;
> +	}
> +
> +	if (saved_filter)
> +		cmdlen += strlen(" if ") + strlen(saved_filter);
> +
> +	if (cmdlen >= MAX_FILTER_STR_VAL) {
> +		kfree(var_hist);
> +		return ERR_PTR(-E2BIG);
> +	}
> +
>  	cmd = kzalloc(MAX_FILTER_STR_VAL, GFP_KERNEL);
>  	if (!cmd) {
>  		kfree(var_hist);
> @@ -3062,28 +3091,24 @@ create_field_var_hist(struct hist_trigger_data *target_hist_data,
>  	}
>  
>  	/* Use the same keys as the compatible histogram */
> -	strcat(cmd, "keys=");
> +	off = scnprintf(cmd, MAX_FILTER_STR_VAL, "keys=");
> +	first = true;
>  
>  	for_each_hist_key_field(i, hist_data) {
>  		key_field = hist_data->fields[i];
> -		if (!first)
> -			strcat(cmd, ",");
> -		strcat(cmd, key_field->field->name);
> +		off += scnprintf(cmd + off, MAX_FILTER_STR_VAL - off, "%s%s",
> +				 first ? "" : ",", 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);
> +	off += scnprintf(cmd + off, MAX_FILTER_STR_VAL - off,
> +			 ":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);
> -	}
> +	if (saved_filter)
> +		scnprintf(cmd + off, MAX_FILTER_STR_VAL - off, " if %s",
> +			  saved_filter);
>  
>  	var_hist->cmd = kstrdup(cmd, GFP_KERNEL);
>  	if (!var_hist->cmd) {