linux-kernel - Re: [PATCH v4] tracing: Replace deprecated strncpy() with strscpy() for stack_trace_filter

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Message-ID: <20250418224555.5b8b8232@batman.local.home>
Date: Fri, 18 Apr 2025 22:45:55 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Devaansh Kumar <devaanshk840@...il.com>
Cc: mhiramat@...nel.org, mathieu.desnoyers@...icios.com,
 linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org,
 skhan@...uxfoundation.org, linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH v4] tracing: Replace deprecated strncpy() with strscpy()
 for stack_trace_filter_buf

On Sat, 19 Apr 2025 03:44:41 +0530
Devaansh Kumar <devaanshk840@...il.com> wrote:

> diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
> index 14c6f272c4d8..0f2253f3bc8c 100644
> --- a/kernel/trace/trace_stack.c
> +++ b/kernel/trace/trace_stack.c
> @@ -542,7 +542,7 @@ 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);
> +		strscpy(stack_trace_filter_buf, str + len, sizeof(stack_trace_filter_buf));

Is the sizeof() needed?

From include/linux/string.h:

/**
 * strscpy - Copy a C-string into a sized buffer
 * @dst: Where to copy the string to
 * @src: Where to copy the string from
 * @...: Size of destination buffer (optional)
 *
 * Copy the source string @src, or as much of it as fits, into the
 * destination @dst buffer. The behavior is undefined if the string
 * buffers overlap. The destination @dst buffer is always NUL terminated,
 * unless it's zero-sized.
 *
 * The size argument @... is only required when @dst is not an array, or
 * when the copy needs to be smaller than sizeof(@dst).
 *
 * Preferred to strncpy() since it always returns a valid string, and
 * doesn't unnecessarily force the tail of the destination buffer to be
 * zero padded. If padding is desired please use strscpy_pad().
 *
 * Returns the number of characters copied in @dst (not including the
 * trailing %NUL) or -E2BIG if @size is 0 or the copy from @src was
 * truncated.
 */
#define strscpy(dst, src, ...)  \
        CONCATENATE(__strscpy, COUNT_ARGS(__VA_ARGS__))(dst, src, __VA_ARGS__)

With stack_trace_filter_buf defined as:

  static char stack_trace_filter_buf[COMMAND_LINE_SIZE+1] __initdata;

This looks like a text book example of just having that be:

		strscpy(stack_trace_filter_buf, str + len);

-- Steve


>  
>  	stack_tracer_enabled = 1;
>  	return 1;