Re: [PATCH v3] tracing: Replace deprecated strncpy() with strscpy() for stack_trace_filter_buf

[Steven Rostedt]

On Fri,  4 Apr 2025 19:28:48 +0530
Devaansh Kumar <devaanshk840@xxxxxxxxx> wrote:

> --- a/kernel/trace/trace_stack.c
> +++ b/kernel/trace/trace_stack.c
> @@ -543,8 +543,10 @@ static __init int enable_stacktrace(char *str)
>  {
>  	int len;
>  
> -	if ((len = str_has_prefix(str, "_filter=")))
> -		strncpy(stack_trace_filter_buf, str + len, COMMAND_LINE_SIZE);
> +	len = str_has_prefix(str, "_filter=");
> +
> +	if (len)
> +		strscpy(stack_trace_filter_buf, str + len, sizeof(stack_trace_filter_buf));
>  
>  	stack_tracer_enabled = 1;
>  	return 1;

BTW, why separate out the len? I use this notation quite a bit for
str_has_prefix() checks.

$ git grep '(len = str_has_pref' kernel/trace
kernel/trace/trace_events.c:    if (!(len = str_has_prefix(fmt, "REC->")))
kernel/trace/trace_events_filter.c:     if ((len = str_has_prefix(str + i, ".ustring"))) {
kernel/trace/trace_events_filter.c:     if ((len = str_has_prefix(str + i, ".function"))) {
kernel/trace/trace_events_hist.c:       if ((len = str_has_prefix(str, "key=")) ||
kernel/trace/trace_events_hist.c:           (len = str_has_prefix(str, "keys="))) {
kernel/trace/trace_events_hist.c:       } else if ((len = str_has_prefix(str, "val=")) ||
kernel/trace/trace_events_hist.c:                  (len = str_has_prefix(str, "vals=")) ||
kernel/trace/trace_events_hist.c:                  (len = str_has_prefix(str, "values="))) {
kernel/trace/trace_events_hist.c:       } else if ((len = str_has_prefix(str, "sort="))) {
kernel/trace/trace_events_hist.c:       } else if ((len = str_has_prefix(str, "clock="))) {
kernel/trace/trace_events_hist.c:       } else if ((len = str_has_prefix(str, "size="))) {
kernel/trace/trace_events_hist.c:               if ((len = str_has_prefix(str, "onmatch(")))
kernel/trace/trace_events_hist.c:               else if ((len = str_has_prefix(str, "onmax(")))
kernel/trace/trace_events_hist.c:               else if ((len = str_has_prefix(str, "onchange(")))
kernel/trace/trace_stack.c:     if ((len = str_has_prefix(str, "_filter=")))

It's fine being in the if statement as the if is more about "does this have
this prefix" and the length is just a side effect of it to use it to
extract the rest.

This patch is only about removing strncpy(), it doesn't need to modify the
format.

-- Steve